Electron diffraction study of crystal structures of (Sr1−xBax)2Nb2O7

Abstract

Selected-area electron diffraction and convergent-beam electron diffraction (CBED) techniques are used to reveal the Ba doping effect on the crystal structure of (${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ba}}_{x}{)}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{7}$ [SBN(x)] in the temperature range from 293 to 693 K. Ba doping of ${\mathrm{Sr}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{7}$ (SN) causes weakening of the incommensurate modulation and deviation from the C-centered lattice. On the other hand, symmetries of fundamental reflections in CBED patterns of SBN(x) are seen to be the same as those of SN, showing a small structural deviation from Cmc${2}_{1}$. Crystal symmetries above and below the temperature of a relaxorlike dielectric anomaly in SBN ($x=0.32$) at 465 K remain unchanged. CBED experiments with a nanometer-sized electron probe do not show any indication of the presence of a nanodomain around this temperature. However, the presence of a few-micron-sized polar-inversion domains is found at around 573 K in SBN ($x=0.32$). The origin of the reported relaxorlike dielectric anomaly in SBN ($x=0.32$) is discussed on the basis of the experimental results of CBED.