Nanoscale phase transformations in relaxor-ferroelectric lead scandium tantalate and lead scandium niobate
Nanoscale phase transformations in relaxor-ferroelectric lead scandium tantalate and lead scandium niobate
复制标题
弛豫铁电钽酸铅钪和铌酸铅钪的纳米级相变
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
M. Aroyo
中科院分区：
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作者：
B. Mihailova;U. Bismayer;B. Güttler;M. Gospodinov;A. Boris;Christian Berndhard;M. Aroyo
用偏振拉曼光谱和远红外椭圆偏振技术研究了PbSc0.5Ta0.5O3(PST)和PbSc0.5Nb0.5O3(PSN)单晶样品在降温过程中发生的结构转变。声子反常的温度演化表明，PST和PSN中存在不同的铁相择优物种。在介电常数附近，PST比PSN在更大的空间范围内发生了铅原子相对于垂直于立方体对角线的氧片的最大协同位移。在降温时，这种结构修饰更有利于PST，从而产生高度各向异性的铁电畴。在PSN中，温度降低有利于B-阳离子偏离BO6-八面体中心，从而导致分布在各向同性基质中的小尺寸极性团簇的形成。在180K附近，PST经历了一个额外的相变，它涉及到旋转对称性的降低。PST中纳米尺度的相变受点缺陷的影响，而不是受长程B位有序度的影响。光谱数据表明，在PSN中，除了常见的钙钛矿结构倍增Pm3̅m-Fm3̅m外，还发生了额外的晶胞倍增。
Abstract Structural transformations that take place on cooling down in Pb-based relaxor ferroelectrics are investigated on the basis of polarized Raman spectroscopy and far infrared ellipsometry applied on single-crystal samples of PbSc0.5Ta0.5O3 (PST) and PbSc0.5Nb0.5O3 (PSN). The temperature evolution of phonon anomalies reveals different preferred ferroic species in PST and PSN. Near the dielectric constant maximum cooperative shifts of Pb atoms in respect to the oxygen sheets perpendicular to the cubic body diagonal occur in larger spatial regions for PST than for PSN. On cooling down this structural modification becomes preferential for PST, thus giving rise to highly anisotropic ferroelectric domains. In PSN the temperature decrease favours B-cation deviations from the BO6-octahedral centres, which leads to formation of small-sized polar clusters distributed in the isotropic matrix. Near 180 K PST undergoes an additional phase transition that involves reduction of the rotation symmetry. The nanoscale phase transformations in PST are affected by the presence of point defects rather than by the degree of long-range B-site ordering. The spectroscopic data give some evidence that in PSN additional multiplication of the unit cell takes place, besides the common perovskite-structure doubling Pm3̅m – Fm3̅m.