Heat capacity measurement of α-Ti-O solid solution doped with vanadium and aluminium from 320 to 910K

Abstract Heat capacities of titanium-oxygen alloys, TiO 0.215 , TiO 0.306 , TiO 0.409 and TiO 0.466 , and those of doped alloys, (Ti 1-y V y ) ~0.2 (y = 0.016 and 0.048) and (Ti 1-y Al y )O ~0.2 (y = 0.03 and 0.05), were measured from 320 to 910K by adiabatic scanning calorimetry. Two kinds of heat capacity anomalies were observed for all samples except the O/Ti composition of 0.466. The anomaly at higher temperatures is assigned to be due to an order-disorder rearrangement of oxygen atoms. Another anomaly obtained at lower temperatures depends on cooling condition, indicating that this anomaly is due to a nonequilibrium phenomenon. The enthalpy and entropy changes due to the order-disorder transition for α-Ti-O solid solution obtained from this experiment are compared with theoretical values. The transition temperature, and enthalpy and entropy changes due to order-disorder transition decrease with increasing dopant contents of vanadium and aluminium, indicating that arrangement of oxygen atoms at lower temperatures may be partially ordered by the interaction between doped metal and oxygen atoms.