LATTICE MODES IN FERROELECTRIC PEROVSKITES - PBTIO3
LATTICE MODES IN FERROELECTRIC PEROVSKITES - PBTIO3
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DOI：
10.1103/physrevb.7.3088
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发表时间：
1973-01-01
影响因子：
3.7
通讯作者：
SCOTT, BA
中科院分区：
文献类型：
--
作者：
BURNS, G;SCOTT, BA
利用拉曼光谱对四元系钙钛矿结构PbTiO 3的晶格动力学行为进行了全面的研究。所有的长波长模式的频率的温度依赖性被确定。我们表明，一个阻尼谐振子模型与频率无关的阻尼系数是足以解释所观察到的形状的软E（1 TO）模式在铁电相在所有温度低于Tc = 493 C。此外，结合我们的实验模式频率数据和热释电测量的自发极化Ps随温度的变化，我们得到Ps（25 C_（max））= 81 μC/cm 2和Ps（Tc）= 42 μC/cm 2。这与最近的直接实验测量非常一致。所有的模式强度的温度依赖性也被确定为Tc。这些结果被用来提取的温度依赖性的钳位介电常数。在PbTiO 3中，沿铁电轴的介电常数沿着ε c主要由最低频率A1（1 TO）模式在所有温度下确定，与BaTiO 3相反，在铁电相中，最低模式仅决定ε c的0.25%。在PbTiO 3中，垂直于c轴的介电常数ε a也由所有温度下的最低E（1 TO）模决定。本文研究了在PbTiO 3的软模数据中观察到临界效应的可能性。未观察到这些影响。此外，它示出，非常仔细的拟合的软模式温度依赖性的功能形式包含最小数量的单独确定的参数之前，可以调用的位移型的一阶相变的临界效应是必需的。
A complete study of the lattice-dynamical behavior of the ferroelectric tetragonal perovskite PbTi O 3 has been carried out using Raman spectroscopy. The temperature dependence of all the long-wavelength mode frequencies are determined. We show that a damped-harmonic-oscillator model with a frequency-independent damping coefficient is sufficient to explain the observed shape of the soft E (1 TO) mode in the ferroelectric phase at all temperatures below T c= 493 C. Moreover, by combining our experimental mode-frequency data with pyroelectric measurements of the change in spontaneous polarization P s with temperature, we obtain values of P s (25 C∘)= 81 μC/cm 2 and P s (T c)= 42 μC/cm 2. This is in excellent agreement with a recent direct experimental measurement. The temperature dependence of all the mode strengths has also been determined to T c. These results are used to extract the temperature dependence of the clamped dielectric constants. In PbTi O 3 the dielectric constant along the ferroelectric axis ε c is determined primarily by the lowest frequency A 1 (1 TO) mode at all temperatures to T c, in contrast to BaTi O 3 where in the ferroelectric phase the lowest mode determines only≈ 2 5% of ε c. In PbTi O 3 the dielectric constant perpendicular to the c axis ε a is also determined by the lowest E (1 TO) mode at all temperatures. The possibility of observing critical effects near T c in the soft-mode data of PbTi O 3 has been examined. These effects are not observed. Also, it is shown that very careful fitting of the soft-mode temperature dependence to a functional form containing a minimum number of separately determined parameters is required before critical effects can be invoked in first-order phase transitions of the displacive type.