Heat Capacity Measurement of Oxygen-Dissolved V–Ti Alloys1

The heat capacities of (V1−y Ti y ) O x alloys (x=0.13 to 0.18, y=0.06 to 0.23) were measured in the temperature range from 380 to 900μK with a differential scanning calorimeter. A λ-type peak corresponding to the order–disorder phase transition was observed in the heat capacity curves of each (V1−y Ti y ) O x alloy (x≦0.18, y≦0.09). The baseline of the measured heat capacity was estimated with the harmonic term and the anharmonic term of the lattice vibration. The entropy changes at the phase transition were determined by subtracting the baseline mentioned above from the measured heat capacities. The experimental entropy changes were in good agreement with those calculated theoretically, based on the arrangement of oxygen and the limited coordination number of oxygen around vanadium. There were no peaks in the heat capacity curves for the samples with compositions y≧0.16. Introduction of titanium, which has a larger ionic radius than that of vanadium, may disturb the ordering of oxygen around the metal.