Fabrication and Crystal Structure of Sol-Gel Deposited BST Thin Films with Compositional Gradient

In the present research technology of compositionally graded barium strontium titanate Ba1-xSrxTiO3 thin films deposited on stainless steel substrates by sol-gel spin coating followed with thermal annealing at T = 650°C is reported. Results of thermal behavior of the sol-gel derived powders with compositions used for fabrication of graded structure (i.e. with Sr mole fraction x = 0.5, 0.4 and 0.3) are described. X-ray diffraction studies of the phase composition and crystal structure of such complex thin film configuration are given. It was found that gel powders exhibited a large total weight loss of about Δm ≈ 44-47%. Three stages of weight loss took place at temperature ranges: below T ≈ 300°C, at ΔT ≈ 300-500°C and between T = 600°C and T = 800°C. Phase analysis has shown that the dominating phase is Ba0.67Sr0.33TiO3 compound while the second phase is Ba0.7Sr0.3TiO3 or Ba0.5Sr0.5TiO3 for "up-graded" and "down-graded" structure, respectively

A new microwave ceramic - Polymer composite with 0-3 connectivity

Goal of the present research was to fabricate and study two-phase BiNbO4//PVDF composites with 0-3 connectivity. Such composite consists of there-dimensionally connected polymer matrix loaded with dielectric ceramic particles. In the present case BiNbO4 powder acted as an active phase(dispersed phase) whereas polyvinylidene fluoride (PVDF) acted as a non-active (passive) phase (matrix). BiNbO4//PVDF composites with the volume fraction of the ceramic phase cV =2, 4, 6, 8, 10, 16 and 20 vol. % were prepared. Average grain size of BiNbO4 powder was =1.86/m. It was found that BiNbO4 powder exhibited orthorhombic symmetry with Pnna (52) space group and PVDF polymer powder was α-phase. Minimum of dielectric losses at room temperature were found within the frequency range Δv =103-104 Hz. It was found that composite with cV =10% of ceramic powder exhibited lower values of dielectric permittivity

Influence of bismuth content on complex immittance characteristics of pressureless sintered BiNbO4 ceramics

Goal of the present research was to study immittance properties of BiNbO4 ceramics fabricated by the solid state reaction route followed by pressureless sintering. Four sets of samples were examined, namely the one fabricated from the stoichiometric mixture of oxides, viz. Bi2O 3 and Nb2O5 as well as the ones with an excess of 3%, 5% and 10% by mole of Bi2O3. The immittance properties were studied by impedance spectroscopy. Measurements were carried out within the frequency range T =20Hz-1MHz and temperature range T =RT-550°C. The Kramers-Kronig data validation test was employed in the impedance data analysis. It was found that complex impedance first increases with an increase in Bi2O3 content and decreases for 10mol% excess of Bi2O3. Two relaxation phenomena manifested themselves at elevated temperature (T >267°C) within the measuring frequency range. The conductivity relaxation phenomenon (M′′(v) spectra) took place at higher frequency than the phenomenon with dominant resistive component (Z′′(v) spectra)

Dielectric properties of bismuth ferrite-bismuth titanate ceramic composite

In this paper the BiFeO3//Bi4Ti3O12 (BF//BiT) ceramic-ceramic composites with 0-3 connectivity were prepared from BiFeO3 and Bi4Ti3O12 ceramic powders by free sintering method at T=900 C, for different concentration of the BF ceramic phases. Bi4Ti3O12 and BiFeO3 ceramic powders were synthesized by the conventional mixed oxide method (MOM). Synthesized BF powder was dispersed in a BiT solution and next such composite was pressing and sintering. Crystalline structure was studied by X-ray diffraction method. The dielectric properties of the BF//BiT ceramic composites were also investigated. Temperature dependence of dielectric permittivity of BF//BiT composites was measured in the frequency range of f =10kHz-100kHz. It was found, that properties of the ceramic-ceramic composite are not a simple sum of properties of the phases constituting the composite but they depend on both the way of connectivity and mutual influence of the phases on each other. The abrupt increase in permittivity may indicate an excess of the percolation threshold, so the ceramic composite for the concentrations of the BF ceramic phase cV >10% cannot be indexed as composites with 0-3 connectivity

Effect of Bi2O3 excess on morphology and structure of BiNbO4 ceramics

Goal of the present research was to fabricate BiNbO4 ceramics from the mixture of powders by the solid state reaction route and pressureless sintering at various temperatures (Ts =870°C and Ts =910°C) and study microstructure, phase composition and crystalline structure of BiNbO4 ceramics. Four batches were fabricated and examined, namely the one fabricated from the stoichiometric mixture of reagent - grade oxide powders, viz. Bi203 and Nb20 5 as well as the ones with an excess of 3%, 5% and 10% by mole of Bi2O3. It was found that apart from the main orthorhombic a-BiNb04 phase additional phases, namely tetragonal Bi 5Nb3015, and cubic Bi3NbO 7 are possible to form from the mixture of bismuth oxide and niobium oxide. It was found that α-BiNbO4 ceramics exhibited the orthorhombic symmetry identified as Pnna (52). However, small differences in elementary cell parameters were found for the samples sintered from stoichiometric and non-stoichiometric mixture of initial powders

Study of phase and chemical composition of Bi1-xNdxFeO3 powders derived by pressureless sintering

In the present paper studies on Bi1-xNdxFeO 3 for x =0.1-0.4 are reported. The mixed oxide method followed with pressureless sintering was employed for ceramics fabrication. Thermal behavior of stoichiometric mixtures of simple oxide powders, viz. Bi2O 3, Nd2O3 and Fe2 O3 was studied by simultaneous thermal analysis. It was found that with an increase in neodymium content the weight loss increased from 0.75% to 3.16% for x =0.1 and x =0.4, respectively. It was found that weight loss took place mainly within two temperature ranges, namely △T1 ≈(300-400)°C and △T2 ≈600-800)°C. Bi 1-xNdxFeO3 ceramics was studied in terms of its phase composition (X-ray phase analysis) and chemical composition (EDS method) at room temperature. It was found that Bi1-xNdxFeO 3 suffered structural phase transition from rhombohedral to orthorhombic symmetry with an increase in neodymium concentration x within the range x =(0.2-0.3)

Wpływ V2O5 na strukturę i właściwości dielektryczne ceramiki BiNbO4

Goal of the present research was to investigate the influence of V 2O5 additive on the structure and dielectric properties of BiNbO4 ceramics. To fabricate BiNbO4 ceramics with V2O5 added the solid state reaction route and pressureless sintering was utilized. Thus obtained ceramics was characterized in terms of its microstructure (SEM), chemical composition (EDS), phase composition and crystalline structure (X-ray phase and structural analysis, respectively). Also dielectric properties in both temperature and frequency domains were investigated. The impedance spectroscopy was utilized for dielectric characterization and the measurements of complex impedance were performed within the frequency range ν =10Hz-1MHz and temperature range T =RT-550°C. It was found that V2O5 additive changed slightly lattice parameters of BiNbO4 ceramics, decreased porosity of samples and revealled relaxation phenomena within the frequency ranges ν =102-103Hz and ν =105-106Hz at temperature T>285°C

Effect of semiconductor element substitution on the electric properties of barium titanate ceramics

The investigated ceramics were prepared by a solid-state reaction from simple oxides and carbonates with the use of a mixed oxide method (MOM). The morphology of BaTi0.96Si0.04O3 (BTSi04) ceramics was characterised by means of a scanning electron microscopy (SEM). It was found that Si+4 ion substitution supported the grain growth process in BT-based ceramics. The EDS results confirmed the high purity and expected quantitative composition of the synthesized material. The dielectric properties of the ceramics were also determined within the temperature range (ΔT=130-500K). It was found that the substitution of Si+4 ions had a significant influence on temperature behavior of the real (ϵ′) and imaginary (ϵ″) parts of electric permittivity as well as the temperature dependence of a.c. conductivity. Temperature regions of PTCR effect (positive temperature coefficient of resistivity) were determined for BTSi04 ceramics in the vicinity of structural phase transitions typical for barium titanate. No distinct maximum indicating a low-temperature structural transition to a rhombohedral phase in BTSi04 was found. The activation energy of conductivity was determined from the Arrhenius plots. It was found that substitution of Si ions in amount of 4wt.% caused almost 50% decrease in an activation energy value

Magnetoelectric effect in (BiFeO3)x-(BaTiO3)1-x solid solutions

The aim of the present work was to study magnetoelectric effect (ME) in (BiFeO3)x-(BaTiO3)1-x solid solutions in terms of technological conditions applied in the samples fabrication process. The rapidly growing interest in these materials is caused by their multiferroic behaviour, i.e. coexistence of both electric and magnetic ordering. It creates possibility for many innovative applications, e.g. in steering the magnetic memory by electric field and vice versa. The investigated samples of various chemical compositions (i.e. x = 0.7, 0.8 and 0.9) were prepared by the solid-state sintering method under three sets of technological conditions differing in the applied temperature and soaking time. Measurements of the magnetoelectric voltage coefficient αME were performed using a dynamic lock-in technique. The highest value of αME was observed for 0.7BiFeO3-0.3BaTiO3 solid solution sintered at the highest temperature (T = 1153 K) after initial electrical poling despite that the soaking time was reduced 10 times in this case

Sol-gel derived (Ba,Sr)TiO3 thin films for tunable devices

The present study is devoted to synthesis and investigation of basic properties of ferroelectric thin films. The sol-gel-type chemical solution deposition method was used for preparation of (Ba0.6Sr0.4)TiO3 (BST) thin films. The thin films were characterized in terms of their microstructure, crystalline structure, chemical composition and dielectric properties. It was found that the BST thin films adopted cubic crystallographic symmetry of the space group Pm3m, whereas the chemical composition of the thin films corresponded well with the chemical composition of the solution. Complex impedance spectroscopy was used to measure frequency-dependent dielectric properties of the thin films. Due to the high tunability and low dielectric loss, great application potential of these ferroelectric thin films was considered especially as tunable dielectric devices