High-temperature properties of the solid solution BaNi2(V1-xPxO4)2

The polycrystalline samples of BaNi2(V1-xPxO4)2 (x = 0-1) were prepared via a solution combustion synthesis. The study of the crystal structure shows that the substitution of vanadium (5+) cations by smaller phosphorus (5+) cations leads to compression of the [Ni2(V1-xPxO4)2]infinity layers in the ab plane with a decrease in the unit cell volume of BaNi2(V1-xPxO4)2. As a result, the BaO12 polyhedra are elongated along the c axis. The melting point increases monotonically with increasing phosphorus concentration. The linear dependence of the relative elongation (Delta L/L0) of samples on temperature after 500 degrees C becomes S-shaped. The electrical conductivity (sigma) of BaNi2(V1-xPxO4)2 was measured in the range of 300-900 degrees C. Electron transfer in BaNi2(V1-xPxO4)2 established to occur along the Ni-O-Ni chains and is explained by the formation of Ni3+.