The bulk nanostructural Bi2Te3-based material was prepared by microwave assisted solvothermal 
method and hot isostatic pressure. Optimal synthesis conditions of the Bi2Te3  nanopowder were found. It 
was established that hot isostatic pressing of the nanopowders at the temperature of 400 С and the pres-sures of 2, 4, 6 and 8 GPa allowed us to prepare the homogeneous and dense Bi2Te3-based material with 
the mean grain size of~50 nm. It is found that an electrical resistivity increases as the mean grain size of 
the material under study decreases.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3638

Ivanov, O.N.

Lyubushkin, R.A.

Soklakova, O.N.

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 6 No 3, 03064(5pp) (2014) Том 6 № 3, 03064(5cc) (2014) 
 
 
The article was reported at the International Conference «The Advanced Technology, Equipment and Analytical Systems for Materials», Kursk, 13-14 May, 2014 
2077-6772/2014/6(3)03064(5) 03064-1  2014 Sumy State University 
Characterization of Bulk Nanostructural Bi2Te3-based Material Prepared by Microwave-
solvothermal Synthesis and Hot Isostatic Pressure 
 
O.N. Ivanov, R.A. Lyubushkin, O.N. Soklakova 
 
Belgorod State National Research University, 85, Pobedy Str., 308015 Belgorod, Russia 
 
(Received 19 May 2014; published online 15 July 2014) 
 
The bulk nanostructural Bi2Te3-based material was prepared by microwave assisted solvothermal 
method and hot isostatic pressure. Optimal synthesis conditions of the Bi2Te3 nanopowder were found. It 
was established that hot isostatic pressing of the nanopowders at the temperature of 400 С and the pres-
sures of 2, 4, 6 and 8 GPa allowed us to prepare the homogeneous and dense Bi2Te3-based material with 
the mean grain size of  50 nm. It is found that an electrical resistivity increases as the mean grain size of 
the material under study decreases. 
 
Keywords: Microwave-solvothermal synthesis, Hot isostatic pressure, Bismuth telluride, Grain structure 
 
 PACS numbers: 68.37.Hk, 68.37.Lp, 68.37.Yz, 
68.47.De 
 
 
1. INTRODUCTION 
 
Thermoelectric materials are of interest for applica-
tions in electrical power generation devices and solid-
state cooling due to many attractive properties (long 
life, no emissions of toxic gases, no moving parts, low 
maintenance, etc) [1]. At present, bismuth telluride, 
Bi2Te3, based compounds are known to be the most ex-
cellent thermoelectric materials for around room tem-
perature applications [2]. The semiconductor bismuth 
telluride materials are acceptable for some specialized 
applications, but they are far less so for commercial 
refrigeration on a large scale. A number of investiga-
tions have focused on optimizing the composition, tun-
ing doping with other heavy metals, optimizing device 
design, etc in order to improve thermoelectric proper-
ties of the Bi2Te3-based materials [3-5]. However, the 
thermoelectric efficiency of these materials has not im-
proved obviously and thermoelectric figure of merit 
(ZT) has been approximately 1 for many years. Figure 
of merit is defined as (S2 / k)T, where Z is the figure-
of-merit, T is the absolute temperature, S is the See-
beck coefficient,  is the electrical conductivity, and k is 
the total thermal conductivity with contributions from 
the lattice and the charge carriers [6]. 
According to theoretical and experimental investi-
gations, the thermoelectric nanomaterials, such as 
quantum wells, superlattices, quantum wires, 
nanograined thin films, bulk nanostructural materials 
including nanocomposites can demonstrate much high-
er thermoelectric coefficients than their traditional 
alternatives [7-10]. 
The bulk nanostructural materials are now consid-
ered to be ones of perspective thermoelectric materials. 
It is assumed that high enough electrical conductivity, 
but low enough lattice thermal conductivity can be for 
the same time reached for these materials. The grain 
size is one of important characteristics optimizing both 
electrical conductivity and thermal conductivity of 
thermoelectric nanomaterials [11].  
A specific technology should be developed to fabri-
cate thermoelectric nanostructural materials with ad-
vanced properties and reproducible phase composition, 
crystal structure and grain arrangement. 
One of technological approaches can be based on two 
principal stages as follows: 
 The synthesis of a starting nanosized powder with 
desired structure, phase and element compositions, size 
and shapes of particles, etc. 
 The consolidation of a synthesized nanopowder by 
using a pressuring and a high temperature treatment 
in order to preserve a nanostructure and fabricate a 
bulk dense material with the high enough mechanical 
strength and thermoelectric parameters.  
In present work such a kind of technology based on 
the microwave-solvothermal synthesis and the hot 
isostatic pressure was applied to prepare the bulk 
nanostructural Bi2Te3-based material. 
 
2. EXPERIMENTAL PROCEDURE 
 
The nanosized bismuth telluride powders have been 
prepared via the microwave-solvothermal synthesis in 
closed reactor ERTEC (Model 02-02). As is known, 
compared with the conventional methods, the micro-
wave-assisted heating technique has the advantages of 
very short time of synthesis, simplicity and energy effi-
ciency, small particle size of the products, narrow par-
ticle size distribution and high purity [12]. 
The analytical grade Bi2O3, TeO2 and ethylene gly-
col were used as starting components. A 110 ml teflon-
lined stainless-steel autoclave was used and the tem-
perature was regulated by a digital-type temperature-
controlled oven. Microwave assisted reactions were 
conducted in a 300 W microwave oven with a 2450 kHz 
working frequency.  
The ethylene glycol was used as both the solvent 
and the reducing agent in the reaction. A few routes of 
synthesis were applied to determine the optimal reac-
tion conditions. After synthesis, the reaction product as 
a black precipitate was washed with alcohol and then 
centrifuged and dried.  
The nanopowders after synthesis were hot isostati-
cally pressed (HIP) at temperature of 400 С during 5 
min by using a toroidal press. The powder for compac-
 O.N. IVANOV, R.A. LYUBUSHKIN, O.N. SOKLAKOVA J. NANO- ELECTRON. PHYS. 6, 03064 (2014) 
 
 
03064-2 
tion was placed in a graphite matrix with hexagonal 
BN powder as a media to spread the isostatic pressure 
to the object under pressing. The HIP-pressure of 2, 4, 
6 and 8 GPa were applied. 
X-ray diffraction (XRD) analysis both the nanopow-
der and the sintered material was performed for phase 
and crystal structure determination using a Rigaku 
Ultima IV diffractometer with CuKα - radiation (a step 
width of 0.03 and a counting time of 1.6 s/step). 
The particles size and morphology of the powders 
were observed using a model JEM – 2100 transmission 
electron microscope (TEM, for an accelerating voltage 
of 200 kV). 
Electrical resistivity measurements were made by 
four-probed method at 1 mA dc current using the sin-
tered samples with Au and In-Ga electrodes. 
 
3. RESULTS AND DISCUSSION 
 
In order to optimize the phase composition of the 
bismuth telluride powders, a few routes of the micro-
wave-solvothermal synthesis, which differ the content 
of the starting reagents and the parameters of synthe-
sis (the temperature, pressure and duration of reac-
tion), were applied (Table 1). According to Table 1, the 
phase composition of the powders is drastically de-
pendent on the synthesis conditions. Only one of syn-
thesis routes allowed us to prepare a single-phase pow-
der of the Bi2Te3 composition. The optimal synthesis 
conditions are as follows: the temperature is 250 C, 
the pressure is 15 atm., the duration of synthesis is 
50 min and the ratio of Bi2O3 and TeO2 is 1 : 1.  
The XRD pattern for the single-phase Bi2Te3 pow-
der taken at room temperature is shown in Figure 1. 
The diffraction peaks can be exactly indexed with the 
standard diffraction planes of hexagonal Bi2Te3. This 
powder synthesized at the optimal conditions was used for 
further examination. 
TEM images in Figures 2 and 3 show typical mor-
phology of microwave-solvothermally synthesized pow-
der. It is seen that the powder mainly consists of irreg-
ularly shaped nanoparticles of 20-50 nm in size (Fig. 2).
 
 
Fig. 1 – XRD pattern of the Bi2Te3 nanopowder 
 
Besides, larger (~ 100 nm) hexagonal nanoplates are in 
the powder under study (Figure 3). The formation of 
the hexagonal Bi2Te3 nanoplates is due to their aniso-
tropic structure. It is known [13] that the Bi2Te3 crystal 
consists of 15 layers stacked along the c-axis and pre-
sents a combination of three hexagonal layer stacks of 
the composition in which each set consists of five atoms 
(Te1–Bi–Te2–Bi–Te1). The bonding within the Te1–Bi–
Te2–Bi–Te1 layer is assumed to be covalent, while the 
bonding between the Te1–Te1 layers is formed by van 
der Waals forces.  
It is known that the growth of grains can occur dur-
ing the long-time and high-temperature sintering of ma-
terial consisting of a starting nanosized powder [14]. 
This phenomenon can destroy nanostructural state of 
material. In order to retain the nanostructure due to 
nanosized powder, the hot isostatic pressure method was 
applied to sinter the bulk nanostructural Bi2Te3-based 
samples. Both the high temperature and the high pres-
sure simultaneously act on the material in this method. 
Therefore, the sintering duration is significantly reduced 
and growth of grains can be assumed to be negligible. 
 
Table 1 – Parameters and results of microwave-solvothermal synthesis of the powders 
 
 
 
 
Reagents  Parameters of synthesis  Phases  
Ethylene glycol – 60 ml  
m (Bi2O3) - 4.6 g  
m (TeO2) – 2.3 g  
Temperature – 280 C  
Pressure – 25 atm.  
Duration of reaction – 100 min.  
Bi2Te3, Bi, BiTe  
Ethylene glycol – 60 ml  
m (Bi2O3) - 4.6 g 
m (TeO2) – 3 g  
Temperature – 280 C 
Pressure – 37 atm.  
Duration  of reaction – 45 min.  
Bi2Te3, Bi, Te  
Ethylene glycol – 60 ml  
m (Bi2O3) – 2.3 g  
m (TeO2) –  1.5 g  
Temperature – 250 C  
Pressure – 30 atm.  
Duration  of reaction – 35 min.  
Bi2Te3, Bi, Bi4Te3  
Ethylene glycol – 60 ml  
m (Bi2O3) – 2.3 g  
m (TeO2) – 2.3 g  
Temperature – 250 C  
Pressure – 15 atm.  
Duration of reaction – 50 min.  
Bi2Te3  
Ethylene glycol – 60 ml  
m (Bi2O3) – 2.3 g  
m (TeO2) – 2.45 g 
Temperature – 250 C 
Pressure – 20 atm. 
Duration of reaction – 35 min.  
Bi2Te3, Bi4Te3 
 CHARACTERIZATION OF BULK NANOSTRUCTURAL BI2TE3-BASED… J. NANO- ELECTRON. PHYS. 6, 03064 (2014) 
 
 
03064-3 
 
 
Fig. 2 – TEM image of the Bi2Te3 nanopowder 
 
 
 
Fig. 3 – TEM image of the hexagonal Bi2Te3 nanoplate 
 
In addition to the temperature, the HIP-pressure is 
one of the important parameters influencing the char-
acteristics of the sample microstructure formed during 
the sintering.  
Figure 4 shows the SEM images of the surfaces of 
the bulk Bi2Te3-based material sintered at the HIP-
pressures of 2, 4, 6 and 8 GPa and at the same temper-
ature (at 400 С) and the same sintering duration (for 5 
min). The materials sintered by the HIP-method have 
dense, homogeneous and porousless, nanocrystalline 
structures. Spherical formations with diameters of 150-
350 nm are observed for the sample with the HIP-
pressure of 2 GPa (Figure 4A). Since the particles size 
of the microwave-solvothermally synthesized powder 
was less than 50 nm (Figure 2), the large spherical 
structures should be considered as agglomerates con-
sisting of a lot of nanoparticles. Smaller spherical par-
ticles can be also seen for this sample. So, the grain 
structure of the bulk polycrystal material is not yet 
formed at 2 GPa. The large spherical agglomerates 
typical for the HIP-pressure of 2 GPa are practically 
absent for other HIP-pressures (Figure 4 B, C and D). 
Only smaller grains mainly with sizes less than 100 nm 
are now observed on the SEM images. The grains have 
a crystal faceting that can be taken as evidence of in-
tense sintering of the nanopowder.  
In order to characterize the HIP-pressure effect on 
the microstructure characteristics in detail, histogram 
of the grain size distributions were plotted (Figure 5). 
Diameters of more than 200 grains were measured on 
the SEM images (Figure 4) to obtain reliable size dis-
tribution. The grain size distributions are discretized 
by dividing them into the 20 nm – width segments. 
 
 
 
 
 
 
 
 
 
Fig. 4 – SEM images of the bulk nanostructural Bi2Te3-based 
material sintered at the various HIP-pressures: 2 (A), 4 (B), 6 
(C) and 8 GPa (D)  
 
The study of the microstructure and elemental 
composition of the transverse sections of samples with 
composite coatings showed that were obtained uniform  
The visible boundary of the coating-substrate inter-
face has no defects. Figure 1 shows that in the contact 
area of coating and substrate is mixed structure con-
sisting of islands covering the substrate a very differ-
ent shapes and sizes. Part of the powder material pene-
trated deeply and firmly connected to the substrate 
material (see. Fig. 1). At impact a large powder parti-
cles, it corrects and deforms the surface layer of the 
substrate. There are "splashes" of the substrate mate-
rial, which are located in surface (see. Table 2). Area of 
the coating thacaused by the shock effect of plasma-
detonation wave. 
 O.N. IVANOV, R.A. LYUBUSHKIN, O.N. SOKLAKOVA J. NANO- ELECTRON. PHYS. 6, 03064 (2014) 
 
 
03064-4 
 
 
a 
 
  
 
b 
 
Fig. 1 – SEM image of cross section of the nanocomposite Ti/H 
coating layer and substrate (a), TEM image of the coating-
substrate interface (b), diffraction TEM photographs of a tran-
sition layer of intermetallic TiAl 
 
3.1 TEM Observation of the System «Nanocom-
posite Coatings - Substrate» 
 
Local phase and structure analysis of the composite 
coatings based on Ti, O, C and H showed that lamellas 
in the coatings consisted of the mixture of titanium 
nanocrystalline grains with face-centered close-packed 
lattice and amorphous phases, and nanoamorphous 
oxide of titanium (see. Fig. 2). This is confirmed by re-
sults of diffraction analysis of the nanocomposite coat-
ings (see. Fig. 3). This structure could be caused by a 
high-temperature cycle in formation of composite coat-
ings [11, 12]. 
Therefore, it can be assumed that the values of 
hardness in fine lamellae of the nanocomposite coat-
ings are attributable to the absence of dislocations in-
side the crystalline grains and ratio of the volume con-
tents of nanocrystalline to amorphous phases of metal-
lic and non-metallic titanium compounds. 
Strength of intermediate and near-interface layers 
leads to increase of deformation resistance of nanocom-
posite coatings. The absence of dislocations inside the 
crystalline grains leads to increase in elasticity and, at 
the same time, in plasticity of nanocomposite coatings. 
It was detected for the first time ever [12], as far back 
as 20-25 years ago, that ceramic materials of titanium 
oxides acquire super plastic properties at room temper-
ature at the characteristic sizes of crystals equal to 
several nanometers. 
 
3.2 XRD Analysis of the Nanocomposite  
Coatings 
 
Carried out phase analysis showed that the main 
phase of the coating layer, which is located at a dis-
tance of about 1-2 mm from the free surface was Ti 
with a face-centered close-packed lattice (a  2.965 Å) 
(see. Fig. 3). The calculated interplanar distances re-
flections suggest the presence in the coatings and the 
following phases: TiO with a cubic lattice (a  4.197 Å), 
rutile TiO2 with tetragonal lattice (a  b  4.585 Å, 
c  2.972 Å), anatase TiO2 with tetragonal lattice 
(a  b  3.775 Å, c  9.492 Å), Ti2O3 with a hexagonal 
lattice (a  b  5.129 Å, c  13.815 Å). In the nanocom-
posite coatings formed from the hydrogenated powder, 
recorded the presence of δ-TiH phase with a cubic lat-
tice (a  4.415 Å) and TiH2 with tetragonal lattice 
(a  b  3.148 Å, c  4.140 Å). The studies did not report 
the presence of boron in the coatings. Apparently this 
is due to the fact that micron particles of amorphous 
boron overheat and evaporate in the environment of 
the combustion products. 
 
      
 
   
 
Fig. 2 – TEM image and diffraction photographs of material of 
nanocomposite coating of TiH powder: mixture of titanium 
nanocrystalline grains with face-centered close-packed lattice 
and amorphous phases (1), amorphous phases (C, Ti, Al, O) 
(2), nanoamorphous oxide of titanium (3) 
 
 
 
Fig. 3 – XRD analysis of the nanocomposite coatings: 1 – Ti/H, 
2 - Ti, 3 – Ti/B, 4 – Ti/B/H 
 
4. CONCLUSIONS 
 
Cumulative-detonation technology provides for-
mation of dense composite coatings based on Ti, O, C, 
H thickness of 100-400 microns. The porosity of coat-
ings was ~ 1-2 %, which correlates with the technologi-
cal requirements of indus-trial coatings. The apparent 
limit of adhesion of the coating to the substrate is free 
of defects. It was found a transition region coat-
ing / substrate consisting of a nanocrystalline TiAl. The 
 CHARACTERIZATION OF BULK NANOSTRUCTURAL BI2TE3-BASED… J. NANO- ELECTRON. PHYS. 6, 03064 (2014) 
 
 
03064-5 
main phases of the composite coatings are Ti, TiO, ru-
tile, anatase, Ti2O3. In the composite coatings formed 
from the hydrogenated powder was recorded the pres-
ence of δ-TiH phase and TiH2.  
Based on the results of the study could be offered 
energy-saving technology for deposition of composite 
coatings based on Ti, O, C, H on substrates of alumi-
num alloy. 
AKNOWLEDGEMENTS 
 
We wish thank Prof. W. Lojkowski for his help in 
the experiment coordination in the Institute of the 
High Pressure Physics, Polish Academy of Sciences, 
Warsaw, Poland. This work was financially supported 
by the Ministry of Education and Science of the Rus-
sian Federation under project No 3.308.2014/K. 
 
 
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3. Y.N. Tyurin, S.G. Polyakov, O.V. Kolisnichenko et. al., 
Protection of Metals and Physical Chemistry of Surfaces, 
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4. Y.N. Tyurin, O.V. Kolisnichenko, I.M. Duda, Strength. 
Technol. Coat. No 5, 27 (2009). 
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6. J. Kawakita, S. Kuroda, Surf. Coat. Tech. 201, 1250 
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7. K. Kim, M. Watanabe, K. Mitsuishi, Proc. of Conf. ‘ITSC 
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8. R. Rezaeian, S. Chromik, E. Yue, J.G. Irissou, Proc. of Conf. 
‘ITSC 2008’ (The Netherlands, Maastrich: June 2-4, 2008). 
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2005’ (Switzerland, Basel: May 2-4, 2005). 
10. R. Blose, Proc. of Conf. ‘ITSC 2005’ (Switzerland, Basel: 
May 2-4, 2005). 
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English

Characterization of Bulk Nanostructural Bi2Te3-based Material Prepared by Microwave-solvothermal Synthesis and Hot Isostatic Pressure

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 6 No 3, 03064(5pp) (2014) Том 6 № 3, 03064(5cc) (2014)   The article was reported at the International Conference «The Advanced Technology, Equipment and Analytical Systems for Materials», Kursk, 13-14 May, 2014 2077-6772/2014/6(3)03064(5) 03064-1  2014 Sumy State University Characterization of Bulk Nanostructural Bi2Te3-based Material Prepared by Microwave-solvothermal Synthesis and Hot Isostatic Pressure  O.N. Ivanov, R.A. Lyubushkin, O.N. Soklakova  Belgorod State National Research University, 85, Pobedy Str., 308015 Belgorod, Russia  (Received 19 May 2014; published online 15 July 2014)  The bulk nanostructural Bi2Te3-based material was prepared by microwave assisted solvothermal method and hot isostatic pressure. Optimal synthesis conditions of the Bi2Te3 nanopowder were found. It was established that hot isostatic pressing of the nanopowders at the temperature of 400 С and the pres-sures of 2, 4, 6 and 8 GPa allowed us to prepare the homogeneous and dense Bi2Te3-based material with the mean grain size of  50 nm. It is found that an electrical resistivity increases as the mean grain size of the material under study decreases.  Keywords: Microwave-solvothermal synthesis, Hot isostatic pressure, Bismuth telluride, Grain structure   PACS numbers: 68.37.Hk, 68.37.Lp, 68.37.Yz, 68.47.De   1. INTRODUCTION  Thermoelectric materials are of interest for applica-tions in electrical power generation devices and solid-state cooling due to many attractive properties (long life, no emissions of toxic gases, no moving parts, low maintenance, etc) [1]. At present, bismuth telluride, Bi2Te3, based compounds are known to be the most ex-cellent thermoelectric materials for around room tem-perature applications [2]. The semiconductor bismuth telluride materials are acceptable for some specialized applications, but they are far less so for commercial refrigeration on a large scale. A number of investiga-tions have focused on optimizing the composition, tun-ing doping with other heavy metals, optimizing device design, etc in order to improve thermoelectric proper-ties of the Bi2Te3-based materials [3-5]. However, the thermoelectric efficiency of these materials has not im-proved obviously and thermoelectric ﬁgure of merit (ZT) has been approximately 1 for many years. Figure of merit is defined as (S2 / k)T, where Z is the figure-of-merit, T is the absolute temperature, S is the See-beck coefficient,  is the electrical conductivity, and k is the total thermal conductivity with contributions from the lattice and the charge carriers [6]. According to theoretical and experimental investi-gations, the thermoelectric nanomaterials, such as quantum wells, superlattices, quantum wires, nanograined thin ﬁlms, bulk nanostructural materials including nanocomposites can demonstrate much high-er thermoelectric coefficients than their traditional alternatives [7-10]. The bulk nanostructural materials are now consid-ered to be ones of perspective thermoelectric materials. It is assumed that high enough electrical conductivity, but low enough lattice thermal conductivity can be for the same time reached for these materials. The grain size is one of important characteristics optimizing both electrical conductivity and thermal conductivity of thermoelectric nanomaterials [11].  A specific technology should be developed to fabri-cate thermoelectric nanostructural materials with ad-vanced properties and reproducible phase composition, crystal structure and grain arrangement. One of technological approaches can be based on two principal stages as follows:  The synthesis of a starting nanosized powder with desired structure, phase and element compositions, size and shapes of particles, etc.  The consolidation of a synthesized nanopowder by using a pressuring and a high temperature treatment in order to preserve a nanostructure and fabricate a bulk dense material with the high enough mechanical strength and thermoelectric parameters.  In present work such a kind of technology based on the microwave-solvothermal synthesis and the hot isostatic pressure was applied to prepare the bulk nanostructural Bi2Te3-based material.  2. EXPERIMENTAL PROCEDURE  The nanosized bismuth telluride powders have been prepared via the microwave-solvothermal synthesis in closed reactor ERTEC (Model 02-02). As is known, compared with the conventional methods, the micro-wave-assisted heating technique has the advantages of very short time of synthesis, simplicity and energy effi-ciency, small particle size of the products, narrow par-ticle size distribution and high purity [12]. The analytical grade Bi2O3, TeO2 and ethylene gly-col were used as starting components. A 110 ml teﬂon-lined stainless-steel autoclave was used and the tem-perature was regulated by a digital-type temperature-controlled oven. Microwave assisted reactions were conducted in a 300 W microwave oven with a 2450 kHz working frequency.  The ethylene glycol was used as both the solvent and the reducing agent in the reaction. A few routes of synthesis were applied to determine the optimal reac-tion conditions. After synthesis, the reaction product as a black precipitate was washed with alcohol and then centrifuged and dried.  The nanopowders after synthesis were hot isostati-cally pressed (HIP) at temperature of 400 С during 5 min by using a toroidal press. The powder for compac- O.N. IVANOV, R.A. LYUBUSHKIN, O.N. SOKLAKOVA J. NANO- ELECTRON. PHYS. 6, 03064 (2014)   03064-2 tion was placed in a graphite matrix with hexagonal BN powder as a media to spread the isostatic pressure to the object under pressing. The HIP-pressure of 2, 4, 6 and 8 GPa were applied. X-ray diffraction (XRD) analysis both the nanopow-der and the sintered material was performed for phase and crystal structure determination using a Rigaku Ultima IV diffractometer with CuKα - radiation (a step width of 0.03 and a counting time of 1.6 s/step). The particles size and morphology of the powders were observed using a model JEM – 2100 transmission electron microscope (TEM, for an accelerating voltage of 200 kV). Electrical resistivity measurements were made by four-probed method at 1 mA dc current using the sin-tered samples with Au and In-Ga electrodes.  3. RESULTS AND DISCUSSION  In order to optimize the phase composition of the bismuth telluride powders, a few routes of the micro-wave-solvothermal synthesis, which differ the content of the starting reagents and the parameters of synthe-sis (the temperature, pressure and duration of reac-tion), were applied (Table 1). According to Table 1, the phase composition of the powders is drastically de-pendent on the synthesis conditions. Only one of syn-thesis routes allowed us to prepare a single-phase pow-der of the Bi2Te3 composition. The optimal synthesis conditions are as follows: the temperature is 250 C, the pressure is 15 atm., the duration of synthesis is 50 min and the ratio of Bi2O3 and TeO2 is 1 : 1.  The XRD pattern for the single-phase Bi2Te3 pow-der taken at room temperature is shown in Figure 1. The diffraction peaks can be exactly indexed with the standard diffraction planes of hexagonal Bi2Te3. This powder synthesized at the optimal conditions was used for further examination. TEM images in Figures 2 and 3 show typical mor-phology of microwave-solvothermally synthesized pow-der. It is seen that the powder mainly consists of irreg-ularly shaped nanoparticles of 20-50 nm in size (Fig. 2).  Fig. 1 – XRD pattern of the Bi2Te3 nanopowder  Besides, larger (~ 100 nm) hexagonal nanoplates are in the powder under study (Figure 3). The formation of the hexagonal Bi2Te3 nanoplates is due to their aniso-tropic structure. It is known [13] that the Bi2Te3 crystal consists of 15 layers stacked along the c-axis and pre-sents a combination of three hexagonal layer stacks of the composition in which each set consists of ﬁve atoms (Te1–Bi–Te2–Bi–Te1). The bonding within the Te1–Bi–Te2–Bi–Te1 layer is assumed to be covalent, while the bonding between the Te1–Te1 layers is formed by van der Waals forces.  It is known that the growth of grains can occur dur-ing the long-time and high-temperature sintering of ma-terial consisting of a starting nanosized powder [14]. This phenomenon can destroy nanostructural state of material. In order to retain the nanostructure due to nanosized powder, the hot isostatic pressure method was applied to sinter the bulk nanostructural Bi2Te3-based samples. Both the high temperature and the high pres-sure simultaneously act on the material in this method. Therefore, the sintering duration is significantly reduced and growth of grains can be assumed to be negligible.  Table 1 – Parameters and results of microwave-solvothermal synthesis of the powders     Reagents  Parameters of synthesis  Phases  Ethylene glycol – 60 ml  m (Bi2O3) - 4.6 g  m (TeO2) – 2.3 g  Temperature – 280 C  Pressure – 25 atm.  Duration of reaction – 100 min.  Bi2Te3, Bi, BiTe  Ethylene glycol – 60 ml  m (Bi2O3) - 4.6 g m (TeO2) – 3 g  Temperature – 280 C Pressure – 37 atm.  Duration  of reaction – 45 min.  Bi2Te3, Bi, Te  Ethylene glycol – 60 ml  m (Bi2O3) – 2.3 g  m (TeO2) –  1.5 g  Temperature – 250 C  Pressure – 30 atm.  Duration  of reaction – 35 min.  Bi2Te3, Bi, Bi4Te3  Ethylene glycol – 60 ml  m (Bi2O3) – 2.3 g  m (TeO2) – 2.3 g  Temperature – 250 C  Pressure – 15 atm.  Duration of reaction – 50 min.  Bi2Te3  Ethylene glycol – 60 ml  m (Bi2O3) – 2.3 g  m (TeO2) – 2.45 g Temperature – 250 C Pressure – 20 atm. Duration of reaction – 35 min.  Bi2Te3, Bi4Te3  CHARACTERIZATION OF BULK NANOSTRUCTURAL BI2TE3-BASED… J. NANO- ELECTRON. PHYS. 6, 03064 (2014)   03064-3   Fig. 2 – TEM image of the Bi2Te3 nanopowder    Fig. 3 – TEM image of the hexagonal Bi2Te3 nanoplate  In addition to the temperature, the HIP-pressure is one of the important parameters influencing the char-acteristics of the sample microstructure formed during the sintering.  Figure 4 shows the SEM images of the surfaces of the bulk Bi2Te3-based material sintered at the HIP-pressures of 2, 4, 6 and 8 GPa and at the same temper-ature (at 400 С) and the same sintering duration (for 5 min). The materials sintered by the HIP-method have dense, homogeneous and porousless, nanocrystalline structures. Spherical formations with diameters of 150-350 nm are observed for the sample with the HIP-pressure of 2 GPa (Figure 4A). Since the particles size of the microwave-solvothermally synthesized powder was less than 50 nm (Figure 2), the large spherical structures should be considered as agglomerates con-sisting of a lot of nanoparticles. Smaller spherical par-ticles can be also seen for this sample. So, the grain structure of the bulk polycrystal material is not yet formed at 2 GPa. The large spherical agglomerates typical for the HIP-pressure of 2 GPa are practically absent for other HIP-pressures (Figure 4 B, C and D). Only smaller grains mainly with sizes less than 100 nm are now observed on the SEM images. The grains have a crystal faceting that can be taken as evidence of in-tense sintering of the nanopowder.  In order to characterize the HIP-pressure effect on the microstructure characteristics in detail, histogram of the grain size distributions were plotted (Figure 5). Diameters of more than 200 grains were measured on the SEM images (Figure 4) to obtain reliable size dis-tribution. The grain size distributions are discretized by dividing them into the 20 nm – width segments.          Fig. 4 – SEM images of the bulk nanostructural Bi2Te3-based material sintered at the various HIP-pressures: 2 (A), 4 (B), 6 (C) and 8 GPa (D)   The study of the microstructure and elemental composition of the transverse sections of samples with composite coatings showed that were obtained uniform  The visible boundary of the coating-substrate inter-face has no defects. Figure 1 shows that in the contact area of coating and substrate is mixed structure con-sisting of islands covering the substrate a very differ-ent shapes and sizes. Part of the powder material pene-trated deeply and firmly connected to the substrate material (see. Fig. 1). At impact a large powder parti-cles, it corrects and deforms the surface layer of the substrate. There are "splashes" of the substrate mate-rial, which are located in surface (see. Table 2). Area of the coating thacaused by the shock effect of plasma-detonation wave.  O.N. IVANOV, R.A. LYUBUSHKIN, O.N. SOKLAKOVA J. NANO- ELECTRON. PHYS. 6, 03064 (2014)   03064-4   a     b  Fig. 1 – SEM image of cross section of the nanocomposite Ti/H coating layer and substrate (a), TEM image of the coating-substrate interface (b), diffraction TEM photographs of a tran-sition layer of intermetallic TiAl  3.1 TEM Observation of the System «Nanocom-posite Coatings - Substrate»  Local phase and structure analysis of the composite coatings based on Ti, O, C and H showed that lamellas in the coatings consisted of the mixture of titanium nanocrystalline grains with face-centered close-packed lattice and amorphous phases, and nanoamorphous oxide of titanium (see. Fig. 2). This is confirmed by re-sults of diffraction analysis of the nanocomposite coat-ings (see. Fig. 3). This structure could be caused by a high-temperature cycle in formation of composite coat-ings [11, 12]. Therefore, it can be assumed that the values of hardness in fine lamellae of the nanocomposite coat-ings are attributable to the absence of dislocations in-side the crystalline grains and ratio of the volume con-tents of nanocrystalline to amorphous phases of metal-lic and non-metallic titanium compounds. Strength of intermediate and near-interface layers leads to increase of deformation resistance of nanocom-posite coatings. The absence of dislocations inside the crystalline grains leads to increase in elasticity and, at the same time, in plasticity of nanocomposite coatings. It was detected for the first time ever [12], as far back as 20-25 years ago, that ceramic materials of titanium oxides acquire super plastic properties at room temper-ature at the characteristic sizes of crystals equal to several nanometers.  3.2 XRD Analysis of the Nanocomposite  Coatings  Carried out phase analysis showed that the main phase of the coating layer, which is located at a dis-tance of about 1-2 mm from the free surface was Ti with a face-centered close-packed lattice (a  2.965 Å) (see. Fig. 3). The calculated interplanar distances re-flections suggest the presence in the coatings and the following phases: TiO with a cubic lattice (a  4.197 Å), rutile TiO2 with tetragonal lattice (a  b  4.585 Å, c  2.972 Å), anatase TiO2 with tetragonal lattice (a  b  3.775 Å, c  9.492 Å), Ti2O3 with a hexagonal lattice (a  b  5.129 Å, c  13.815 Å). In the nanocom-posite coatings formed from the hydrogenated powder, recorded the presence of δ-TiH phase with a cubic lat-tice (a  4.415 Å) and TiH2 with tetragonal lattice (a  b  3.148 Å, c  4.140 Å). The studies did not report the presence of boron in the coatings. Apparently this is due to the fact that micron particles of amorphous boron overheat and evaporate in the environment of the combustion products.             Fig. 2 – TEM image and diffraction photographs of material of nanocomposite coating of TiH powder: mixture of titanium nanocrystalline grains with face-centered close-packed lattice and amorphous phases (1), amorphous phases (C, Ti, Al, O) (2), nanoamorphous oxide of titanium (3)    Fig. 3 – XRD analysis of the nanocomposite coatings: 1 – Ti/H, 2 - Ti, 3 – Ti/B, 4 – Ti/B/H  4. CONCLUSIONS  Cumulative-detonation technology provides for-mation of dense composite coatings based on Ti, O, C, H thickness of 100-400 microns. The porosity of coat-ings was ~ 1-2 %, which correlates with the technologi-cal requirements of indus-trial coatings. The apparent limit of adhesion of the coating to the substrate is free of defects. It was found a transition region coat-ing / substrate consisting of a nanocrystalline TiAl. The  CHARACTERIZATION OF BULK NANOSTRUCTURAL BI2TE3-BASED… J. NANO- ELECTRON. PHYS. 6, 03064 (2014)   03064-5 main phases of the composite coatings are Ti, TiO, ru-tile, anatase, Ti2O3. In the composite coatings formed from the hydrogenated powder was recorded the pres-ence of δ-TiH phase and TiH2.  Based on the results of the study could be offered energy-saving technology for deposition of composite coatings based on Ti, O, C, H on substrates of alumi-num alloy. AKNOWLEDGEMENTS  We wish thank Prof. W. Lojkowski for his help in the experiment coordination in the Institute of the High Pressure Physics, Polish Academy of Sciences, Warsaw, Poland. This work was financially supported by the Ministry of Education and Science of the Rus-sian Federation under project No 3.308.2014/K.   REFERENCES  1. H. Gleiter, Acta mater. 48, 1 (2000). 2. P.H. Mayrhofer, C. Mitterer, L. Hiltman, H. Clements, Prog. Mater. Sci. 51 No 8, 1032 (2006). 3. Y.N. Tyurin, S.G. Polyakov, O.V. Kolisnichenko et. al., Protection of Metals and Physical Chemistry of Surfaces, 48 No 1, 80 (2012). 4. Y.N. Tyurin, O.V. Kolisnichenko, I.M. Duda, Strength. Technol. Coat. No 5, 27 (2009). 5. S. Babin, V. Karpov, Techn. Light Alloys 1-2, 202 (2006). 6. J. Kawakita, S. Kuroda, Surf. Coat. Tech. 201, 1250 (2006). 7. K. Kim, M. Watanabe, K. Mitsuishi, Proc. of Conf. ‘ITSC 2008’ (The Netherlands, Maastrich: June 2-4, 2008). 8. R. Rezaeian, S. Chromik, E. Yue, J.G. Irissou, Proc. of Conf. ‘ITSC 2008’ (The Netherlands, Maastrich: June 2-4, 2008). 9. Fr.-W. Bach, K. Möhwald, D. Kolar, Proc. of Conf. ‘ITSC 2005’ (Switzerland, Basel: May 2-4, 2005). 10. R. 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Characterization of Bulk Nanostructural Bi2Te3-based Material Prepared by Microwave-solvothermal Synthesis and Hot Isostatic Pressure

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