Octahedral distortion, phase structural stability, and microwave dielectric properties in equivalently substituted LaTiNbO ₆ ceramics

Abstract

Abstract The room‐temperature phase composition, microstructural characteristic, and microwave dielectric properties of equivalently substituted LaTiNbO 6 ceramics were investigated by means of the Rietveld structural refinement, scanning electron microscopy, and network analyzer. A special interest was focused on the influence of the variation in bond length and octahedral distortion on the phase structural stability. A monoclinic (M) aeschynite phase was obtained in B‐site ions (Ta 5+ and [W 0.5 Ti 0.5 ] 5+ ) substituted LaTiNbO 6 ceramics while an orthorhombic (O) aeschynite structure appeared in B‐site ions (Zr 4+ ) or A‐site ions (Ce 3+ and Sm 3+ ) substituted LaTiNbO 6 ceramics, which owned typical polygonal and short rod‐like grain morphologies, respectively. Compared with the octahedral bond length, a straightforward relation between the phase structural stability and the octahedral distortion was established, in which a reduced octahedral distortion was directly correlated with the destabilization of O or M phases or vice versa, irrespective of the substitution ionic radius. The experimentally observed giant difference in dielectric performance of LaTiNbO 6 based ceramics was believed to mainly originate from their distinct phase structure and grain morphology.