Structural properties of Ca10.5-xNix(VO4)7 orthovanadates: XRD study at ambient and non-ambient conditions

Orthovanadates have attracted significant research attention due to their potential applications across various fields, including optoelectronics, biomedicine, and catalysis. In this presentation, we explore the structural properties of a novel calcium orthovanadate, specifically Ca_10.5-xNi_x(VO₄)₇, where some of the calcium ions have been partially replaced by nickel ions. We investigate these properties at both, room temperature and non-ambient conditions, through X-ray diffraction measurements. High-resolution X-ray powder diffraction experiments were conducted at the ID22 beamline at ESRF. The study of diffraction patterns at non-ambient temperatures indicates that the structure remains unchanged with temperature varies from 4 K to 1100 K, as confirmed by Rietveld refinements. In this work, we determine the unit cell size and atomic positions of Ca_10.5-xNi_x(VO₄)₇ as functions of temperature. Additionally, we calculate the thermal expansion coefficient for these materials in relation to temperature using various models.