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首页> 外文期刊>Philosophical magazine, B. Physics of condensed matter, electronic, optical, and magnetic properties >Ultrasonic study of the elastic and nonlinear acoustic properties of single-crystal triglycine sulphate in the ferroelectric and paraelectric phases
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Ultrasonic study of the elastic and nonlinear acoustic properties of single-crystal triglycine sulphate in the ferroelectric and paraelectric phases

机译：超声研究铁电和顺电相中单晶硫酸三甘氨酸的弹性和非线性声学特性

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An experimental ultrasonic study has been made of the elastic and nonlinear acoustic behaviour of single-crystal triglycine sulphate (TGS) in both the ferroelectric and paraelectric phases. The ultrasonic wave velocities for 12 modes of vibration propagated along the [100], [010], [001] and [101] directions have been measured as functions of temperature in the range 293-338 K, which covers the Curie temperature T-C, and hydrostatic pressure up to 0.2 GPa at selected temperatures in the same temperature range. The results provide ten out of the 13 elastic stiffness tensor components C-ij of TGS (the exceptions being C-12, C-23 and C-25) and their hydrostatic-pressure derivatives as a function of temperature. Marked anomalies are observed in the C-ij(T) in the vicinity of T-C, with that for C-33 being the most pronounced. The elastic stiffness tensor component C-22, which determines the temperature dependence of the velocity of longitudinal ultrasonic waves propagated along the ferroelectric axis, shows normal behaviour without any anomaly near Tc. The temperature dependences of C-ij are discussed in the framework of existing theoretical models. The pressure derivatives (partial derivative C-ij/partial derivative P)(P=0) of the elastic stiffness tensor components are all positive; application of hydrostatic pressure does not induce acoustic-mode softening. The hydrostatic-pressure derivative (partial derivative C-22/partial derivative P)(P=0) increases approximately linearly with increasing temperature in both the ferroelectric and paraelectric phases without any marked anomaly in the phase transition region. The Values obtained for the remaining (C-ij/partial derivative P)(P=0) increase slightly with increasing temperature in the ferroelectric phase and show a step-like decrease at the phase transition. Using the values determined for C-ij and (partial derivative C-ij/partial derivative P)(P=0), the acoustic-mode Gruneisen parameters have been calculated in the pseudo-orthorhombic approximation. All mode Gruneisen parameters are positive and considerably larger in the ferroelectric phase than in the paraelectric phase. With the exception of that determined for the longitudinal mode along the ferroelectric axis, each mode Gruneisen parameter exhibits a stepwise decrease at the phase transition. The results establish that a pronounced change in the anharmonic coupling takes place between the zone-centre acoustic modes and the spontaneous polarization as the crystal is transformed from the ferroelectric to the paraelectric phase. [References: 47]
机译：已经对单晶硫酸三甘氨酸（TGS）在铁电相和顺电相中的弹性和非线性声学行为进行了实验性超声研究。已经测量了沿着[100]，[010]，[001]和[101]方向传播的12种振动模式的超声波速度随温度的变化，范围为293-338 K，覆盖了居里温度TC，在相同温度范围内的选定温度下，静水压力高达0.2 GPa。结果提供了TGS的13个弹性刚度张量分量C-ij中的十个（C-12，C-23和C-25除外）以及它们的静水压力导数随温度的变化。在T-C附近的C-ij（T）中观察到明显的异常，其中C-33的异常最为明显。弹性刚度张量分量C-22决定了沿铁电轴传播的纵向超声波速度的温度依赖性，它显示出正常的行为，在Tc附近没有任何异常。在现有理论模型的框架内讨论了C-ij的温度依赖性。弹性刚度张量分量的压力导数（偏导数C-ij /偏导数P）（P = 0）均为正。施加静水压力不会引起声模软化。在铁电相和顺电相中，静水压导数（偏导数C-22 /偏导数P）（P = 0）随温度的升高而近似线性增加，而在相变区域则没有任何明显的异常。剩余的（C-ij /偏导数P）（P = 0）的值随铁电相中温度的升高而略有增加，并在相变时呈阶梯状降低。使用确定的C-ij和（偏导数C-ij /偏导数P）（P = 0）的值，以拟斜方波近似法计算了声模Gruneisen参数。在铁电相中，所有模态Gruneisen参数都是正值，并且比顺电相中的参数大得多。除了为沿着铁电轴的纵向模式确定的参数外，每个模式的Gruneisen参数在相变处都显示出逐步减小的趋势。结果表明，当晶体从铁电相转变为顺电相时，在区域中心的声模与自发极化之间会发生非谐耦合的明显变化。 [参考：47]

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