Synthesis and phase transition of negative thermal expansion materials Zr1−xLuxW2O8−y

Zr 1− x Lu x W 2 O 8− y solid solutions were newly synthesized by a solid sate reaction method. X-ray diffraction (XRD) experiments from 90 to 560 K revealed that the solid solutions were of a single phase up to x = 0.04 and showed a negative thermal expansion. Order–disorder phase transition temperatures ( T trs ) and saturated order parameters ( η s ) associated with WO 4 orientational order were determined from the XRD results. The linear relationship between the normalized T trs and η s obtained for Zr 1− x M x W 2 O 8− y (M = Sc, Y, In) in our previous study was also found for Zr 1− x Lu x W 2 O 8− y . A heat capacity anomaly due to the order–disorder phase transition was detected for Zr 0.96 Lu 0.04 W 2 O 8− y by a relaxation calorimeter. T trs of the solid solutions drastically decreased with increasing Lu content. The drastic suppression of T trs can be explained by the model assuming the existence of a local nano-region including the WO 4 pairs having the orientational disorder.