RAMAN-STUDY OF THE STRUCTURAL PHASE-TRANSITION IN THE ORDERED PEROVSKITE PB2MGWO6

Lead magnesium tungstate Pb2MgWO6 undergoes a structural phase transit ion at about 310 K. This phase transition has been characterized by Ra man spectroscopy. The main features of the Raman spectra, collected be tween 173 and 523 K, are consistent with group theoretical predictions though unexpected weak and broad signals are observed in the high-tem perature phase. From the comparison between these results and the stru ctures previously determined, it is concluded that the phase transitio n has a behaviour intermediate between pure displacive and order-disor der.