Raman study of Cu-doped K-1-xLixTa1-yNbyO3

The temperature evolution of TO1 Raman spectra was investigated in single crystals of K1.xLixTa1-yNbyO3:Cu with different Li and Nh amounts. Auxiliary observations of TO4 spectra were also performed. in a sample with x = 0.002 and y = 0.025 and containing 190 ppm of Cu, the results indicate a clear-cut transition to an ordered phase around 55 K, in good agreement with previous findings from dielectric measurements in the same crystal. However, no evidence was found of a role of Cu in this structural modification. Samples with x = 0.01 and y = 0.003 revealed features of an order-disorder phase transition around 45 K, irrespective of the presence of Cu.