Phase transition and near-zero thermal expansion properties of Zr0.5Hf0.5V2-xPxO7 (0 ≤ x ≤ 1.2)

In the study, Zr_0.5Hf_0.5V_2-xP_xO₇ (0 ≤ x ≤ 1.2) was prepared by solid state method and then the microstructure of synthesized samples was investigated. The microstructure, coefficient of thermal expansion (CTE) and phase transition of Zr_0.5Hf_0.5V_2-xP_xO₇ (0 ≤ x ≤ 1.2) were investigated with thermal dilatometry, x-ray diffraction (XRD) and Raman spectroscopy. The results showed that the samples were single cubic phase with the space group of Pa 3 bar in the crystal structure. When the substitution rate of P⁵⁺ was higher than 0.6, the 3 × 3 × 3 superstructure disappeared. The expansion coefficient of Zr_0.5Hf_0.5V_1.2P_0.8O₇ was calculated to be -0.53 × 10^-6 K^-1 under the linear thermal expansion in a very wide temperature range from 300 to 573 K. With the increase of P⁵⁺ content, the temperatures of positive-to-negative thermal expansion of Zr_0.5Hf_0.5V_2-xP_xO₇ firstly even decreased below room temperature and then increased. The synthesized Zr_0.5Hf_0.5V_2-xP_xO₇ exhibited near zero thermal expansion behavior in a wide temperature range around room temperature.