Enhancement of Electrical Conduction and Phonon Scattering in Ga2O3(ZnO)9-In2O3(ZnO)9 Compounds by Modification of Interfaces at the Nanoscale

The Ga2O3(ZnO)9 and In2O3(ZnO)9 homologous phases have attracted attention as thermoelectric (TE) oxides due to their layered structures. Ga2O3(ZnO)9 exhibits low thermal conductivity, while In2O3(ZnO)9 possesses higher electrical conductivity. The TE properties of the solid solution of Ga2O3(ZnO)9-In2O3(ZnO)9 were explored and correlated with changes in the crystal structure. High-quality (1−x)Ga2O3(ZnO)9-(ZnO)9 (x = 0.0 to 1.0) ceramics were prepared by the solid-state route using B2O3 and Nd2O3 as additives. The crystal structures were analysed by x-ray diffraction, high-resolution transmission electron microscopy and atomic resolution scanning transmission electron microscopy–high-angle annular dark field imaging–energy dispersive x-ray spectroscopy (STEM–HAADF–EDS) techniques. A layered superstructure with compositional modulations was observed in all samples in the (1−x)Ga2O3(ZnO)9-xIn2O3(ZnO)9 system. All the ceramics exhibited nanoscale structural features identified as Ga- and In-rich inversion boundaries (IBs). Substitution of 20 mol.% In (x = 0.2) in the Ga2O3(ZnO)9 compounds generated basal and pyramidal indium IBs typically found in the In2O3(ZnO)m system. The (Ga0.8In0.2)2O3(ZnO)9 compound does not exhibit the structural features of the Cmcm Ga2O3(ZnO)9 compound, which is formed by a stacking of Ga-rich IBs along the pyramidal plane of the wurtzite ZnO, but features that resemble the crystal structure exhibited by the R3¯¯¯m In2O3(ZnO)m with basal and pyramidal indium IBs. The structural changes led to improved TE performance. For example, (Ga0.8In0.2)2O3(ZnO)9 showed a low thermal conductivity of 2 W/m K and a high power factor of 150 μW/m K2 giving a figure of merit (ZT) of 0.07 at 900 K. This is the highest ZT for Ga2O3(ZnO)9-based homologous compounds and is comparable with the highest ZT reported for In2O3(ZnO)9 homologous compounds

Utilising unit-cell twinning operators to reduce lattice thermal conductivity in modular structures: Structure and thermoelectric properties of Ga₂O₃(ZnO)₉

The Ga2O3(ZnO)m family of homologous compounds have been identified as potential thermoelectric materials, but properties are often limited due to low densification. By use of B2O3 as an effective liquid phase sintering aid, high density, high quality ceramic samples of Ga2O3(ZnO)9 have been synthesised. The atomic structure and local chemical composition of Ga2O3(ZnO)9 have been determined by means of high resolution X-ray diffraction and atomic resolution STEM-HAADF, EDS and EELS measurements. X-ray analysis showed that the compound crystalizes in the Cmcm orthorhombic symmetry. Atomically resolved HAADF-STEM images unambiguously showed the presence of nano-sized, wedge-shaped twin boundaries, parallel to the b-axis. These nano-scale structural features were chemically investigated, for the first time, revealing the exact distributions of Zn and Ga; it was found that Ga ions occupy sites at the junction of twin boundaries and inversion boundaries. HAADF-EDS analysis showed that the calcination step has a significant impact on crystal structure homogeneity. By use of a sintering aid and optimization of processing parameters the ceramics achieved a low thermal conductivity of 1.5–2.2 W/m.K (for the temperature range 300–900 K), a power factor of 40–90 μW/K.m2, leading to a ZT of 0.06 at 900 K. The work shows a route to exploit nanoscale interface features to reduce the thermal conductivity and thereby enhance the thermoelectric figure of merit in complex thermoelectric materials

Crystallization of Al-Co-Dy(Ho) amorphous alloys

Amorphous ribbons of Al92-x Co8Dy(Ho) (x) (x = 6 and 10 at.%) composition were produced by a standard planar flow casting method. Their kinetics of crystallization was studied by X-rays, DSC and electric resistivity. The phase composition was determined at each stage of crystallization. In order to increase the stability of amorphous state, use of alloy with high REM content and holmium is preferred to dysprosium

Crystallization of Al-Co-Dy(Ho) amorphous alloys

Amorphous ribbons of Al92-x Co8Dy(Ho) (x) (x = 6 and 10 at.%) composition were produced by a standard planar flow casting method. Their kinetics of crystallization was studied by X-rays, DSC and electric resistivity. The phase composition was determined at each stage of crystallization. In order to increase the stability of amorphous state, use of alloy with high REM content and holmium is preferred to dysprosium

The influence of silver content on structure and properties of Sn-Bi-Ag solder and Cu/solder/Cu joints

The authors gratefully acknowledge the financial support of the Slovak Grant Agency under the Contracts VEGA 2/6160/26 and 2/0111/11. This work was also supported by the Slovak Research and Development Agency under the Contracts APVV-0102-07, APVV-0076-11, APVV-0492-11 and APVV-SK-UA-0043-09 and by CEX FUN-MAT. V.S. gratefully acknowledges the fellowship of the Slovak Academic Information Agency. This research contributes to the European COST Action MP0602 on Advanced Solder Materials for High Temperature Applications.The effect of silver content on structure and properties of Sn100-xBi10Agx (x=3-10 at%) lead-free solder and Cu-solder-Cu joints was investigated. The microstructure of the solder in both bulk and rapidly solidified ribbon forms was analyzed by scanning electron microscopy (SEM) and X-ray diffraction. The peculiarities in melting kinetic, studied by differential scanning calorimetry (DSC), and silver influence on it are described and discussed. The wetting of a copper substrate was examined by the sessile drop method in the temperature range of 553-673 K in air and deoxidizing gas (N-2+10%H-2) at atmospheric pressure. Cu-solder-Cu joints were also prepared in both atmospheres, and their shear strength was measured by the push-off method. The produced solders consisted of tin, bismuth and Ag3Sn phases. The product of the interaction between the solder and the copper substrate consists of two phases: Cu3Sn, which is adjacent to the substrate, and a Cu6Sn5 phase. The wetting angle in air increased slightly as the silver concentration in the solder increased. Wetting of the copper substrate in N-2+10H(2) gas shows the opposite tendency: the wetting angle slightly decreased as the silver content in the solder increased. The shear strength of the joints prepared in air (using flux) tends to decrease with increasing production temperature and increasing silver content in the solder. The equivalent decrease in the shear strength of the joints prepared in N-2+10H(2) is more apparent. (C) 2013 Elsevier B.V. All rights reserved

The influence of silver content on structure and properties of Sn-Bi-Ag solder and Cu/solder/Cu joints

The authors gratefully acknowledge the financial support of the Slovak Grant Agency under the Contracts VEGA 2/6160/26 and 2/0111/11. This work was also supported by the Slovak Research and Development Agency under the Contracts APVV-0102-07, APVV-0076-11, APVV-0492-11 and APVV-SK-UA-0043-09 and by CEX FUN-MAT. V.S. gratefully acknowledges the fellowship of the Slovak Academic Information Agency. This research contributes to the European COST Action MP0602 on Advanced Solder Materials for High Temperature Applications.The effect of silver content on structure and properties of Sn100-xBi10Agx (x=3-10 at%) lead-free solder and Cu-solder-Cu joints was investigated. The microstructure of the solder in both bulk and rapidly solidified ribbon forms was analyzed by scanning electron microscopy (SEM) and X-ray diffraction. The peculiarities in melting kinetic, studied by differential scanning calorimetry (DSC), and silver influence on it are described and discussed. The wetting of a copper substrate was examined by the sessile drop method in the temperature range of 553-673 K in air and deoxidizing gas (N-2+10%H-2) at atmospheric pressure. Cu-solder-Cu joints were also prepared in both atmospheres, and their shear strength was measured by the push-off method. The produced solders consisted of tin, bismuth and Ag3Sn phases. The product of the interaction between the solder and the copper substrate consists of two phases: Cu3Sn, which is adjacent to the substrate, and a Cu6Sn5 phase. The wetting angle in air increased slightly as the silver concentration in the solder increased. Wetting of the copper substrate in N-2+10H(2) gas shows the opposite tendency: the wetting angle slightly decreased as the silver content in the solder increased. The shear strength of the joints prepared in air (using flux) tends to decrease with increasing production temperature and increasing silver content in the solder. The equivalent decrease in the shear strength of the joints prepared in N-2+10H(2) is more apparent. (C) 2013 Elsevier B.V. All rights reserved

Magnetic susceptibility of CoFeBSiNb alloys in liquid state

The authors gratefully acknowledge the financial support of the Slovak Grant Agency under the contract VEGA 2/0111/11 and the Slovak Research and Development Agency under the contract APVV-0647-10, APVV-0413-06, APVV-0492-11 and by CEX FUN-MAT. V.S. gratefully acknowledges the fellowship of the Slovak Academic Information Agency. The work is partially supported by RFBR, project N 13-03-00598-a.The influence of small additions of gallium and antimony on magnetic susceptibility of the bulk glass forming Co47Fe20.9B21.2Si4.6Nb6.3 alloy was studied in a wide temperature range up to 1830K by the Faraday's method. The undercooling for all the samples was measured experimentally. Both Ga and Sb additions were found to increase liquidus and solidification temperatures. However, gallium atoms strengthen interatomic interaction in the melts, whereas antimony atoms reduce it (C) 2013 Elsevier B.V. All rights reserved

Nanoscaled Al-AlN composites consolidated by equal channel angular pressing (ECAP) of partially in situ nitrided Al powder

Nanoscaled aluminium nitride (AlN) reinforced aluminium matrix composites were fabricated using a novel approach where powder mixtures of Al+Mg+Sn were partially in situ nitrided in flowing nitrogen followed by consolidation through equal channel angular pressing (ECAP). The resulting composites contain up to 23.8. vol% of AlN with relative density >98%. The microstructure shows two distinctively different alternate lamellar regions. One is the Al matrix free of AlN and the other is composed of nanoscaled AlN embedded in the Al matrix. The Al-AlN composites fabricated this way exhibited attractive properties, including thermal stability up to 450 °C, high compressive strength, high Young's modulus and low coefficient of thermal expansion. The presence of nanoscaled AlN reduced the thermal conductivity of the composites compared to the high thermal conductivity of Al-AlN composites prepared by metal infiltration techniques

The Influence of Thermomagnetic Treatment on the Magnetoelastic Characteristics of Fe₆₁Co₁₉Si₅B₁₅ Amorphous Alloys

Information about magnetoelastic properties of newly developed amorphous magnetic alloys is very important from practical point of view, especially in the case of high permeability materials such as the Fe₆₁Co₁₉Si₅B₁₅ amorphous alloy. In the case of such materials, effect connected with the influence of external stresses on the magnetic properties of the alloy should be tested. This paper presents experimental results of the magnetoelastic properties investigation of the Fe₆₁Co₁₉Si₅B₁₅ amorphous alloy, annealed without magnetic field as well as in the magnetic field. Such thermo-magnetic treatment generated anisotropy has significant influence on the total free energy of magnetic material. In the magnetoelastic investigation, the compressive stress was applied to the ring shaped core, perpendicularly to the magnetizing field direction. Due to the fact, that cores with closed magnetic circuits were used, demagnetization did not change the balance of total free energy in the material

Magnetic susceptibility of CoFeBSiNb alloys in liquid state

The authors gratefully acknowledge the financial support of the Slovak Grant Agency under the contract VEGA 2/0111/11 and the Slovak Research and Development Agency under the contract APVV-0647-10, APVV-0413-06, APVV-0492-11 and by CEX FUN-MAT. V.S. gratefully acknowledges the fellowship of the Slovak Academic Information Agency. The work is partially supported by RFBR, project N 13-03-00598-a.The influence of small additions of gallium and antimony on magnetic susceptibility of the bulk glass forming Co47Fe20.9B21.2Si4.6Nb6.3 alloy was studied in a wide temperature range up to 1830K by the Faraday's method. The undercooling for all the samples was measured experimentally. Both Ga and Sb additions were found to increase liquidus and solidification temperatures. However, gallium atoms strengthen interatomic interaction in the melts, whereas antimony atoms reduce it (C) 2013 Elsevier B.V. All rights reserved