Sr1-xCaxTiO3（x=0.02，0.04）极相自发极化值异常低的结构基础：铁电有序的证据
Structural Basis for the Anomalously Low Spontaneous Polarisation Values of the Polar Phase of Sr1-xCaxTiO3 (x=0.02, 0.04): Evidence for a Ferrielectric Ordering
摘要：
在12至300 K温度范围内，使用Sr 1-xCaxTiO 3（x=0.02，0.04）的X射线粉末衍射轮廓的全图案Le-Bail精修揭示了由于反铁畸变而在170，225 K下的晶胞参数的异常（立方到四方I4/mcm）相变和在~32，~34 K由于转变为极性相（四方I4/mcm到正交Ic 2 m）。我们获得的较低的转变温度与Bednorz和Muller基于介电研究报告的结果非常一致，[10]他们将这些归因于铁电转变。Rietveld分析的极性相的衍射分布揭示了偏心位移的Sr 2 +/Ca 2+和Ti 4+离子在X-Y平面沿<110>伪立方方向，与实验报告的方向容易极化Bednorz和Muller，但是所得到的偶极矩显示为沿着[001]在相邻的（001）平面中铁电耦合。方向导致在12 K下自发极化的异常低值。
英文摘要：
Full pattern Le-Bail refinement using x-ray powder diffraction profiles of Sr1-xCaxTiO3 for x=0.02, 0.04 in the temperature range 12 to 300 K reveals anomalies in the unit cell parameters at 170, 225 K due to an antiferrodistortive (cubic to tetragonal I4/mcm) phase transition and at ~32, ~34 K due to a transition to a polar phase (tetragonal I4/mcm to orthorhombic Ic2m), respectively. The lower transition temperatures obtained by us are in excellent agreement with those reported on the basis of the dielectric studies by Bednorz and Muller, [10] who attributed these to ferroelectric transition. Rietveld analysis of the diffraction profiles of the polar phase reveals off-centre displacements of both Sr2+/Ca2+ and Ti4+ ions in the X-Y plane along <110> pseudocubic directions, in agreement with the experimentally reported direction of easy polarization by Bednorz and Muller, but the resulting dipole moments are shown to be ferrielectrically coupled in the neighbouring (001) planes along the [001] direction leading to anomalously low values of the spontaneous polarization at 12K.
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