LATTICE AND SOFT MODE RAMAN-SPECTRUM OF PBHASO4

The Raman spectrum of PbHAsO4 (LHA) has been studied for the first tim e as a function of temperature between 10 and 320 K (T-C similar to 31 3 K). Symmetry assignments of the lattice modes in LHA have been made with the help of results from the Raman spectrum of PbHPO4 (LHP). A so ft mode is observed at 72.2 cm(-1)-at 10 K. The soft mode in LHA exhib its a weaker temperature dependence compared with the equivalent mode at 74.9 cm(-1) at 10 K in LHP. A comparison of Raman results for LHA a nd LHP shows that the soft mode does not drive the ferroelectric trans ition in either LHA or LHP.