1. b-direction anomalous thermal expansion behavior in SmCrO3.
- Author
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Zhang, Ruoxuan, Cui, Yimin, Yuan, Xiuliang, Wei, Huanqi, and Sun, Ying
- Subjects
- *
THERMAL expansion , *X-ray powder diffraction , *DIELECTRIC measurements , *LATTICE constants , *DIFFRACTION patterns , *CRYSTAL grain boundaries - Abstract
The ceramic composites of Sm 1- x Bi x CrO 3 (x = 0, 0.1, 0.2, 0.3) have been prepared by solid state reaction. X-ray diffraction patterns demonstrate that Bi-doped polycrystalline samples match with standard pattern of SmCrO 3. After Bi doping, the lattice constants in three directions increase slightly. The thermal expansion properties were studied by X-ray powder diffraction over the temperature range from 100 to 400 K. The results showed that the compound SmCrO 3 exhibits positive thermal expansion behavior in the a and c directions in the whole measurement temperature range. The anomaly is that in the b direction the lattice exhibits positive thermal expansion behavior at low temperatures, while above 200 K it exhibits near zero thermal expansion behavior. The thermal expansion behaviors of all Bi-doped SmCrO 3 are similar to that of SmCrO 3 , but unexpectedly, negative thermal expansion behaviors were observed in the b direction above 200 K in the highly Bi doped samples. The dielectric measurement shows that there are two thermal activation processes in all Sm 1- x Bi x CrO 3 (x = 0, 0.1, 0.2, 0.3) respectively, with the low-temperature activation corresponding to the grain itself, while the high-temperature activation comes from the grain boundary. After low-temperature thermal activation, with increasing temperature, the enhanced vibration of the corner oxygen atoms of the CrO 6 octahedron is mainly perpendicular to the b axis, which leads to the near zero thermal expansion behavior in the b direction. Moreover, after high-temperature thermal activation, as the temperature increases, the enhanced interaction between Bi3+ and the free oxygen atom (space oxygen atom) at the grain boundary will further lead to the negative thermal expansion behavior in the b-direction of the high concentration doped samples. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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