Heat capacity measurement of ZrOx and (Zr1−yNby)Ox from 325 TO 905 K

Abstract

Heat capacities of zirconium-oxygen alloys, ZrOx (x = 0.17, 0.20, 0.28 and 0.31), and those of niobium doped alloys, (Zr~-yNby)Ox (x = 0.17 and 0.28, y = 0.005 and 0.01), were measured from 325 to 905 K by an adiabatic scanning calorimeter. Two kinds of heat capacity anomalies were observed for all samples. The anomaly at higher temperatures was assigned to be due to an order-disorder rearrangement of oxygen atoms. Another anomaly at lower temperatures was due to a non-equilibrium phenomenon. The entropy change due to the order-disorder transition for Zr-O solid solution at higher temperature obtained from this experiment was compared with the theoretical value. The transition temperature, transition enthalpy and entropy changes due to the order-disorder transition decreased with increasing niobium contents, indicating that arrangement of oxygen atoms in lower temperature phase may be partially disordered by the interaction between niobium and oxygen atoms.

Thermodynamic evaluation of the Nb–O–Zr system

“…Tsuji et al [36] have measured the heat capacities of Zr-O alloys, ZrO x , for x = 0.17, 0.20, 0.28 and 0.31 and those of niobium doped alloys, (ZrO 1Ày / Nb y )O x , for x = 0.17 and 0.28 and y = 0.005 and 0.01, in the temperature range of 325-905 K by an adiabatic scanning calorimeter. They observed two kinds of heat capacity anomalies at two different temperatures in the specimens.…”

Electric field gradients at 181Ta sites in HfOx

“…It is known that the interstitial oxygen atoms dissolved in titanium [1] and zirconium [2] metals form ordered structures at low temperatures and cause order-disorder transitions between 600 and 800 K. Hafnium also belongs to the same IVA group as titanium and zirconium metals. Oxygen dissolves in hafnium metal up to 20 at% (O/ Hf ¼ 0.25) [3,4] and these dissolved interstitial oxygen atoms form ordered structures similar to those of titaniumand zirconium-oxygen solid solutions [5].…”