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

Abstract In the study, Zr 0.5 Hf 0.5 V 2−x P x O 7 (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 0.5 Hf 0.5 V 2−x P x O 7 (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 ¯ 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 0.5 Hf 0.5 V 1.2 P 0.8 O 7 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 0.5 Hf 0.5 V 2−x P x O 7 firstly even decreased below room temperature and then increased. The synthesized Zr 0.5 Hf 0.5 V 2−x P x O 7 exhibited near zero thermal expansion behavior in a wide temperature range around room temperature. Highlights • Near-zero thermal expansion behavior over a wide temperature range. • The samples are of single-phase cubic type with space group Pa 3 ¯ at RT. • The samples have low phase change temperature. • From superstructure to ideal crystal structure between 310 and 323 K. • CTE was measured by dilatometer to be 0.59 × 10−6 K−1 (310 ∼ 673 K). [ABSTRACT FROM AUTHOR]