INFRARED REFLECTION OF BA(MG1/3TA2/3)O3 CERAMICS

The dielectric function -of the ordered Ba(Mg1/3Ta2/3)O3 ceramics was investigated by the infrared reflectance spectra taken over the 50-4000-cm-1 range. The detailed crystal structure of the specimen was examined by the Rietveld method. The space group of trigonal D3d3 and the degree of long-range order of 0.97 for Mg and Ta atomic arrangement were confirmed. The reflectance spectra were analyzed on the basis of the four-parameter semiquantum model assuming 16 infrared active vibrational modes allowed for the related D3d3 structure. The lowest-frequency optical mode was found at 60 cm-1, which can be assumed to involve the motions of the heavy TaO6 octahedra.