RAMAN STUDY OF TRIGONAL-CUBIC PHASE TRANSITIONS IN RARE-EARTH ALUMINATES

The Raman spectra of LaAlO3, PrAlO3, and NdAlO3 have been observed at temperatures from 10 to 1135°K. Each of these materials evidences a nominally second-order trigonal cubic phase transition; that in LaAlO3 has previously been analyzed by other workers on the basis of x-ray, EPR, and inelastic neutron scattering; however, evidence for the transitions in PrAlO3 [at (1320±20)°K] and NdAlO3 [at (1640±30) °K] is presented here for the first time. In each material, the phase transition is due to the collapse of the Γ25 mode at the R point of the high-temperature cubic Brillouin zone. Modes associated with Γ25 and Γ15 are observed in the trigonal phase in each crystal. © 1969 The American Physical Society.