o-Liang Xia

Order–disorder transition and thermal conductivity of (Yb x Nd1− x )2Zr2O7 solid solutions

X-ray diffraction, transmission electron microscopy and a laser-flash method were used to investigate the order–disorder transition and thermal conductivity of (Yb x Nd1− x )2Zr2O7 (0 ≤ x ≤ 1.00) solid solutions. The structures were found to be pyrochlore-type for 0 ≤ x ≤ 0.25, defect fluorite for 0.45 ≤ x ≤ 1.00 and a mixture of these at 0.30 ≤ x ≤ 0.40. The thermal conductivities of (Yb x Nd1− x )2Zr2O7 first gradually decrease with increasing temperature, and then increase slightly above 800°C due to the increased radiation contribution. YbNdZr2O7 has the lowest thermal conductivity due to the reduced cation mean free path at the compositional combination of equal molar Yb3+ and Nd3+ cations.

Preparation and Improved Grain Conductivity of ( Sm1 − x Y x ) 2Zr2O7 Ceramics

(Sm 1-x Y x ) 2 Zr 2 O 7 (0 ≤ x ≤ 0.5) ceramics were prepared by a solid-state reaction process at 1973 K for 10 h in air. (Sm 1-x Y x ) 2 Zr 2 O 7 (0 ≤ x ≤ 0.3) ceramics have a single phase of the pyrochlore-type structure, whereas (Sm 1-x Y x ) 2 Zr 2 O 7 (x = 0.4,0.5) exhibit a defective fluorite-type structure. The full width at half-maxima in the Raman spectra increase with increasing Y content, which indicates that the degree of structural disorder increases as the yttrium content increases. The electrical conductivity of (Sm 1-x Y x ) 2 Zr 2 O 7 ceramics was investigated by electrochemical impedance spectroscopy over a frequency range of 1 Hz to 20 MHz in the temperature range of 623-1173 K in air and hydrogen atmospheres. The electrical conductivity of (Sm 1-x Y x ) 2 Zr 2 O 7 obeys the Arrhenius-type behavior and increases with increasing temperature. The grain conductivity and total conductivity of pyrochlore-type materials are clearly higher than those of defective fluorite-type materials in the intermediate temperature range of 623-1073 K. Both activation energy and pre-exponential factor for grain conductivity increase with increasing Y content. The electrical conductivity measured in the reducing atmosphere of hydrogen shows no significant changes, which proves that the conduction is purely ionic with negligible electronic contribution in the series.

Coprecipitation synthesis and sintering property of (YbxSm1-x)2Zr2O7 ceramic powders

Abstract Abstract (YbxSm1-x)2Zr2O7 (0<x<1·0) ceramic powders were synthesised with chemical coprecipitation and calcination method. Thermal decomposition behaviour of precipitates was studied by differential scanning calorimetry-thermogravimetry. The powders were characterised by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy. The synthesised powders have a particle size of about 100 nm, and exhibit to a certain extent agglomeration. The sintering behaviour of (YbxSm1-x)2Zr2O7 powders was studied by pressureless sintering method at 1550-1700°C for 10 h in air. The relative densities of (YbxSm1-x)2Zr2O7 ceramics increase with increasing sintering temperature, and reach above 95% when sintered at 1700°C for 10 h in air. Sm2Zr2O7 and (Yb0·1Sm0·9)2Zr2O7 ceramics have a pyrochlore structure; however, (YbxSm1-x)2Zr2O7 (0·3<x<1·0) ceramics exhibit a defective fluorite type structure.

Electrical conductivity of Nd and Ce co-doped Gd2Zr2O7 ceramics

In this study, (Gd1− x Nd x )2(Zr1− x Ce x )2O7 (0 ≤ x ≤ 0.5) ceramics have been prepared by pressureless sintering at 1973 K to investigate the influence of Nd and Ce co-doping on their electrical conductivity. The electrical conductivity of the ceramics was investigated by impedance spectroscopy measurements from 723 to 1173 K over the frequency range of 20 Hz to 2 MHz in air. The measured values obey the Arrhenius relation. For each composition, the grain conductivity gradually increases with increasing temperature from 723 to 1173 K. At a given temperature, it gradually decreases with increasing neodymium and cerium contents from x = 0 to 0.3; thereafter, the grain conductivity exhibits a slight increase with further increasing neodymium and cerium contents up to x = 0.5.