Raman scattering and infrared reflectivity study of orthorhombic/monoclinic LaTiNbO6 microwave dielectric ceramics by A/B-site substitution

Abstract The structure origin of microwave dielectric properties in A/B-site substituted LaTiNbO 6 ceramics with different crystal structures was explored by means of Raman scattering and infrared reflection spectra. Compared with the monoclinic (M) phase, the broadening of the Raman modes associated with B-O stretching and bending vibrations in the orthorhombic (O) phase was believed to be a result of the increased octahedral distortion. The Raman mode at 659 cm −1 was assigned to the stretching vibration of B–O–B and O–B–O bonds in the unique interlayer chain structure of O phase. The Raman modes of the BO 6 tilting within 340–520 cm −1 suggest that different octahedral connection ways should be one of the vital reasons why M and O phases own opposite-sign temperature coefficient of resonance frequency τ f . Moreover, the result of infrared reflection spectrum fitted with a four-parameter semiquantum model indicates that the dielectric response of both M and O phases would mainly originate from the A-BO 6 external vibrations in the far-infrared frequency, particularly their AO 8 structure units. These results would provide useful insights into the structure-property relation in the RETi(Nb,Ta)O 6 (RE: rare earth) material system.