Phase relations in the Zn2V2O7-Cu2V2O7 system from room temperature to melting

Phase relations in the Zn2V2O7-Cu2V2O7 system were studied by high-temperature X-ray diffraction and differential thermal analysis. The major phase constituents of the system are solid solutions based on Zn2V2O7 and Cu2V2O7 polymorphs and their coexistence regions. The generation of α-Zn2 − 2xCu2xV2O7 solid solution, where 0 ≤ x ≤ 0.30, leaves almost unchanged the stabilization temperature of the high-temperature zinc pyrovanadate phase. The α-Cu2 − 2xZn2xV2O7 homogeneity range is 5 mol % Zn2V2O7. In the range 0.050 ≤ x ≤ 0.09 from 20 to ∼ 620°C, there is the two-phase field of α-Cu2V2O7 and β-Cu2V2O7 base solid solutions. At still higher temperatures, β-Zn2 − 2xCu2xV2O7 and α-Cu2 − 2xZn2xV2O7 coexist in the mixed-phase region. β-Zn2 − 2xCu2xV2O7 solid solution, where 0 ≤ x ≤ 0.30, exists above 610 ± 5°C. The extent of the β′-Cu2V2O7-base solid solution is 9 to 65 mol % Zn2V2O7 at 615 ± 5°C, expanding to 0 mol % Zn2V2O7 with rising temperature.