Fabrication and negative thermal expansion properties of P-substituted ZrV2O7 sintered bodies

Calcined powders of ZrV1.2P0.8O7 (ZVP) and ZrV2O7 (ZV) were synthesized by heating gels prepared from NH4H2PO4, NH4VO3, and ZrOCl2 solutions at 500 and 400 °C, respectively. Dense ZV-added ZVP sintered bodies were subsequently fabricated through heating at 850 °C for 20 h, with the addition of ZrV2O7 as a sintering additive. The resulting material had a relative density of ca. 92%, while the relative density of pure sintered ZVP was ca. 72%. NH4H2PO4 (NHP) was also added to ZVP along with ZV to obtain a molar ratio of P in NHP for V in ZV = 1. Subsequently, a single phase (NHP, ZV)-added ZVP sintered body was obtained by heating at 850 °C. Thermomechanical analysis showed that the dense ZV-added ZVP sintered body exhibited a positive thermal expansion from 25 to 150 °C and a negative thermal expansion from 150 to 500 °C.