Structural features and thermoelectric properties of Al-doped (ZnO)(5)In2O3 homologous phases

In this work, we investigated the influence of Al doping on the structure of the (ZnO)(5)In2O3 homologous phase and the thermoelectric characteristics of (ZnO)(5)(In1-xAlx)(2)O-3 ceramics for x=0, 0.01, 0.03, 0.05, 0.1, and 0.2, prepared using a classic ceramic procedure and sintering at 1500 degrees C for 2 hours. The Al substituted for In on both the primary sites in the Zn-5(In1-xAlx)(2)O-8 homologous phase, the octahedral sites in the basal-plane inversion boundaries and the trigonal bi-pyramidal sites in the zig-zag inversion boundaries, which resulted in a uniformly increased shrinkage of the unit cell with the additions of Al. The a and c parameters were reduced for x=0.2 by a maximum 0.8%. All the samples had similar microstructures, so the differences in the TE characteristics mainly resulted from the effects of the substitution of Al for In, decreasing the charge-carrier concentration and affecting their mobility. Slightly improved TE characteristics were only observed for Al additions with x=0.01-0.05, while larger additions of Al only resulted in a reduced electrical conductivity and decreased ZT values in comparison to the un-doped composition

Phase formation, microstructure development and thermoelectric properties of (ZnO)(k)In2O3 ceramics

International audienceThe (ZnO)(k)In2O3 system is interesting for applications in the fields of thermoelectrics and optoelectronics. In this study we resolve the complex homologous phase evolution with increasing temperature in polycrystalline ceramics for k = 5, 11 and 18 and its influence on the microstructural development and thermoelectric properties. The phase formation at temperatures above 1000 degrees C is influenced by the local ZnO-to-In2O3 ratio in the starting-powder mixture. While the equilibrium phase for k = 5 is formed directly after sintering at 1200 degrees C, the formation of the k = 11 and k =18 equilibrium phases proceeds at higher temperatures by diffusion between the initially formed phases, the lower k Zn5In2O8/Zn7In2O10 and the higher k ZnkIn2Ok+3 (9 < k < infinity)Such phase formation affects the sintering and grain growth, and consequently, with the degree of structural and compositional homogeneity, also the thermoelectric characteristics of the (ZnO)(k)In2O3 ceramics. (C) 2017 Elsevier Ltd. All rights reserved

Phase formation, microstructure development and thermoelectric properties of (ZnO)(k)In2O3 ceramics

International audienceThe (ZnO)(k)In2O3 system is interesting for applications in the fields of thermoelectrics and optoelectronics. In this study we resolve the complex homologous phase evolution with increasing temperature in polycrystalline ceramics for k = 5, 11 and 18 and its influence on the microstructural development and thermoelectric properties. The phase formation at temperatures above 1000 degrees C is influenced by the local ZnO-to-In2O3 ratio in the starting-powder mixture. While the equilibrium phase for k = 5 is formed directly after sintering at 1200 degrees C, the formation of the k = 11 and k =18 equilibrium phases proceeds at higher temperatures by diffusion between the initially formed phases, the lower k Zn5In2O8/Zn7In2O10 and the higher k ZnkIn2Ok+3 (9 < k < infinity)Such phase formation affects the sintering and grain growth, and consequently, with the degree of structural and compositional homogeneity, also the thermoelectric characteristics of the (ZnO)(k)In2O3 ceramics. (C) 2017 Elsevier Ltd. All rights reserved

Structural features and thermoelectric properties of Al-doped (ZnO)(5)In2O3 homologous phases

International audienceIn this work, we investigated the influence of Al doping on the structure of the (ZnO)(5)In2O3 homologous phase and the thermoelectric characteristics of (ZnO)(5)(In1-xAlx)(2)O-3 ceramics for x=0, 0.01, 0.03, 0.05, 0.1, and 0.2, prepared using a classic ceramic procedure and sintering at 1500 degrees C for 2 hours. The Al substituted for In on both the primary sites in the Zn-5(In1-xAlx)(2)O-8 homologous phase, the octahedral sites in the basal-plane inversion boundaries and the trigonal bi-pyramidal sites in the zig-zag inversion boundaries, which resulted in a uniformly increased shrinkage of the unit cell with the additions of Al. The a and c parameters were reduced for x=0.2 by a maximum 0.8%. All the samples had similar microstructures, so the differences in the TE characteristics mainly resulted from the effects of the substitution of Al for In, decreasing the charge-carrier concentration and affecting their mobility. Slightly improved TE characteristics were only observed for Al additions with x=0.01-0.05, while larger additions of Al only resulted in a reduced electrical conductivity and decreased ZT values in comparison to the un-doped composition

Phonon Scattering and Electron Doping by 2D Structural Defects in In/ZnO

International audienceIn/ZnO bulk compounds have been synthesized using a simple solid-state process. In this study, both the structural features and thermoelectric properties of the Zn1-xInxO series with ultralow indium content (0 <= x <= 0.02) have been studied. High-angle annular dark-field scanning transmission electron microscopy analyses highlight that indium has the ability to create multiple basal plane and pyramidal defects that produce ZnO domains with inverted polarity starting from dopant concentrations as low as 0.25 atom %. Interestingly, the formation of parallel inversion boundaries consisting of InO6 octahedra in the ZnO4 tetrahedra matrix is responsible for phonon scattering while increasing electrical conductivity, thereby enhancing the thermoelectric properties. This effect of multiple extended two-dimensional defects on the thermoelectric properties of ZnO is reported for the first time with such low indium doping. On the chemistry side, the present results point toward a lack of In solubility in the ZnO structure. Moreover, this study is a step forward to the synthesis of other thermoelectric compounds where dopant-induced planar defects in bulk transition metal compounds have the potential to enhance both phonon scattering and electronic conductivity

Phonon Scattering and Electron Doping by 2D Structural Defects in In/ZnO

In/ZnO bulk compounds have been synthesized using a simple solid-state process. In this study, both the structural features and thermoelectric properties of the Zn1-xInxO series with ultralow indium content (0 <= x <= 0.02) have been studied. High-angle annular dark-field scanning transmission electron microscopy analyses highlight that indium has the ability to create multiple basal plane and pyramidal defects that produce ZnO domains with inverted polarity starting from dopant concentrations as low as 0.25 atom %. Interestingly, the formation of parallel inversion boundaries consisting of InO6 octahedra in the ZnO4 tetrahedra matrix is responsible for phonon scattering while increasing electrical conductivity, thereby enhancing the thermoelectric properties. This effect of multiple extended two-dimensional defects on the thermoelectric properties of ZnO is reported for the first time with such low indium doping. On the chemistry side, the present results point toward a lack of In solubility in the ZnO structure. Moreover, this study is a step forward to the synthesis of other thermoelectric compounds where dopant-induced planar defects in bulk transition metal compounds have the potential to enhance both phonon scattering and electronic conductivity