NEW DEFECT PYROCHLORE SOLID SOLUTION IN THE KBi2M5O16 – TlBi2M5O16 (M=Nb, Ta) SYSTEMS

Synthesis and caraterization of new solids solutions K1-xTlxBi2M5O16 with (0≤x≤1; M=Nb, Ta) defect pyrochlore type. Two solid solutions K1-xTlxBi2M5O16 (0≤x≤1; M=Nb, Ta) were prepared using solid state reaction method and characterized by x-ray diffraction and Infrared absorption spectroscopy. All compositions were indexed in the cubic system (space group Fd3m) and showed the defect pyrochlore-type structure like oxides as ABi2M5O16 (A=K, Tl; M=Nb, Ta) [1]. The cell parameter of the two defect pyrochlores solid solutions varies linearly with increasing x of compositions from a=10.5701(1) Å to a=10.5343(1) Å for K1-xTlxBi2Nb5O16 (0≤x≤1) and from a=10.5489(1) Å to a=10.5144(1) Å for K1-xTlxBi2Ta5O16 (0≤x≤1). Résumé – Synthèse et caractérisation de nouvelles solutions solides K1-xTlxBi2M5O16 (0≤x≤1; M=Nb, Ta) de type pyrochlore déficitaire. Deux solutions solides K1-xTlxBi2M5O16 (0≤x≤1; M=Nb, Ta) ont été préparées à l’état solide et caractérisées par diffraction des rayons X et par spectroscopie d’absorption infrarouge. Toutes les compositions des solutions solides cristallisent dans le système cubique (groupe d’espace Fd3m) et appartiennent à la famille des pyrochlores déficitaires, ABi2M5O16 (A=K, Tl; M=Nb, Ta) [1]. Le paramètre de maille des deux solutions solides varie linéairement avec la composition x de a=10.5701(1) Å à a=10.5343(1) Å pour K1-xTlxBi2Nb5O16 (0≤x≤1) et de a=10.5489(1) Å à a=10.5144(1) Å pour K1-xTlxBi2Ta5O16 (0≤x≤1).Synthesis and caraterization of new solids solutions K1-xTlxBi2M5O16 with (0≤x≤1; M=Nb, Ta) defect pyrochlore type. Two solid solutions K1-xTlxBi2M5O16 (0≤x≤1; M=Nb, Ta) were prepared using solid state reaction method and characterized by x-ray diffraction and Infrared absorption spectroscopy. All compositions were indexed in the cubic system (space group Fd3m) and showed the defect pyrochlore-type structure like oxides as ABi2M5O16 (A=K, Tl; M=Nb, Ta) [1]. The cell parameter of the two defect pyrochlores solid solutions varies linearly with increasing x of compositions from a=10.5701(1) Å to a=10.5343(1) Å for K1-xTlxBi2Nb5O16 (0≤x≤1) and from a=10.5489(1) Å to a=10.5144(1) Å for K1-xTlxBi2Ta5O16 (0≤x≤1). Résumé – Synthèse et caractérisation de nouvelles solutions solides K1-xTlxBi2M5O16 (0≤x≤1; M=Nb, Ta) de type pyrochlore déficitaire. Deux solutions solides K1-xTlxBi2M5O16 (0≤x≤1; M=Nb, Ta) ont été préparées à l’état solide et caractérisées par diffraction des rayons X et par spectroscopie d’absorption infrarouge. Toutes les compositions des solutions solides cristallisent dans le système cubique (groupe d’espace Fd3m) et appartiennent à la famille des pyrochlores déficitaires, ABi2M5O16 (A=K, Tl; M=Nb, Ta) [1]. Le paramètre de maille des deux solutions solides varie linéairement avec la composition x de a=10.5701(1) Å à a=10.5343(1) Å pour K1-xTlxBi2Nb5O16 (0≤x≤1) et de a=10.5489(1) Å à a=10.5144(1) Å pour K1-xTlxBi2Ta5O16 (0≤x≤1)

Nouveaux matériaux ABi2B5O16 (A=Na, Ag, K, Rb, Tl ET B = Bb, Ta) de type pyrochlore déficitaire

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Comparative Study of Sb2O3 (Sb2O5) and Ta2O5 Doping Effects with TeO2 on Electrical Properties of delta-Bi2O3

23rd Conference on Applied Crystallography, Krynica Zdroj, POLAND, SEP 20-24, 2015International audienceIn this study, Sb2O3 (Sb2O5) and Ta2O5 are used as co-dopants with TeO2 to stabilize the delta phase of bismuth oxide (delta-Bi2O3). Some compositions with formula (1 x) BiO1.5-(x /4) Sb2Te2O9 and (1 - x) BiO1.5-(x/4) Ta2Te2O9 (x = 0.1, 0.2, 0.3, 0.6, and 0.9) have been synthesized by solid state reaction at 850 degrees C and characterized by powder X-ray diffraction. The Bi0.9Sb0.05Te0.05O1.575, Bi0.9Ta0.05Te0.05O1.575 and Bi0.8Ta0.1Te0.1O1.65 retain a cubic fluorite structure of delta-Bi2O3 phase. The electric properties were studied by impedance spectroscopy. All samples were evaluated by calculating conductivities and activation energies. Various impedance model including constant phase element and the Warburg impedances have been used to interpret the Nyquist representations of electrical analyses

Crystal structure and phase transitions in new series of double perovskite oxides Ba2-xSrxCaTeO6 (0≤x≤2): X-ray diffraction and Raman spectroscopy studies

The structure stability of double perovskite ceramics Ba2-xSrxCaTeO6 (0≤x≤2) has been studied using X-ray powder diffraction (XRD) and Raman spectroscopy. According to the Rietveld refinement three phases transition induced by composition were reported. The transition from the cubic symmetry to tetragonal (Fmm → I4/m) is observed between x= 0.4 and 0.6. The second transition from tetragonal symmetry to monoclinic symmetry with I2/m as space group takes place between x = 0.6 and 0.8.  The third phase transition monoclinic to monoclinic (I2/m → P21/n) is located between x = 1.4 and 1.6. Furthermore, considerable changes of the composition dependence of the Raman modes recorded at ambient conditions confirm the phase transitions reported by X-ray studies.

Crystal structure and phase transitions in new series of double perovskite oxides Ba2‐xSrxCaTeO6 (0≤x≤2): X‐ray diffraction and Raman spectroscopy studies

The structure stability of double perovskite ceramics Ba2‐xSrxCaTeO6 (0≤x≤2) has been studied using X‐ray powder diffraction (XRD) and Raman spectroscopy. According to the Rietveld refinement three phase transitions induced by compositional changes are reported. The transition from the cubic symmetry to tetragonal (Fm m → I4/m) is observed for x between 0.4 and 0.6. The second transition from tetragonal symmetry to monoclinic symmetry with I2/m as a space group takes place between x = 0.6 and 0.8. The third phase transition, monoclinic to monoclinic (I2/m → P21/n), is located between x = 1.4 and 1.6. Furthermore, considerable changes of the compositional dependence of the Raman modes recorded at ambient conditions confirm occurance of the phase transitions revealed by the X‐ray studies