Phonon analysis and crystal chemical simulation of dielectrics based on sub-millimeter wave ellipsometry

发展了亚毫米波椭圆偏振光谱仪来研究钛酸钡的尺寸效应和钛酸钡基弛豫体的相变行为。椭偏仪是一种测量反射光偏振态变化来确定材料复介电常数的设备。对所研制的椭偏仪的准确性进行了验证，并用它直接测量了钛酸钡单晶的复介电常数。在尺寸效应方面，当颗粒尺寸大于1.1μm时，介电常数随颗粒尺寸的减小而增大，当颗粒尺寸小于1μm时，介电常数随颗粒尺寸的减小而减小，BaTiO_3颗粒中的磁畴大部分为简单的片层结构，90°磁畴宽度随颗粒尺寸的减小而减小。基于宽带介电谱，研究了介电常数的磁区贡献。在晶粒尺寸大于1μm的BaTiO_3陶瓷中，磁畴密度越高，其偶极极化率和离子极化率越高。相反，对于晶粒尺寸小于1μm的BaTiO_3陶瓷，这些极化率被削弱。对于钛酸钡基弛豫体的相变，测量了BaTiO_3(BT)、BaT_3(BST-0.6)和BaZr_(0.25)&GT；Ti_(&lt)；0.75&gt；O_3(BZT-0.25)的宽带介电谱。BST-0.6和BZT-0.25在介电最高温度(T_M)附近的偶极极化行为可以用极性纳米区域(PNRs)的行为来解释，而BT中的铁电区对偶极极化有贡献。BT的驰豫可以解释为极化行为从正常铁电到DPT弛豫铁电体的连续变化。

Sub-millimeter wave spectroscopic ellipsometry has been developed to study the size effect of barium titanate and the phase transition behaviors of barium titanate-based relaxors. Ellipsometer is equipment which measures the change of polarizing state of reflected light to determine the complex dielectric permittivity of materials. Accuracy of the ellipsometer developed in this study was verified and the complex permittivity of a barium titanate single crystal was directly determined using it. S for the size effect, the permittivity of barium titanate ceramics increased with decreasing grain size when the grain size was over 1.1μm, while that decreased when the grain size was below 1μm. Most of the domains in BaTiO_3 grains had simple lamellar structures, and 90° domain width decreased with decreasing grain size. Based on wide band dielectric spectroscopy, the domain contribution to the permittivity was investigated. In BaTiO_3 ceramics with grain sizes over 1μm, the dipole and ionic polarizabilities were enhanced by the high domain density. In contrast, for the BaTiO_3 ceramics with grain sizes below 1μm, these polarizabilities were weakened. As for the phase transition of barium titanate-based relaxors, wideband dielectric spectra from kHz to THz were measured for ceramics of BaTiO_3 (BT), Ba_<0.6>Sr_<0.4>TiO_3 (BST-0.6) and BaZr_<0.25>Ti_<0.75>O_3 (BZT-0.25). The behavior in the dipole polarization near the dielectric maximum temperature (T_m) in BST-0.6 and BZT-0.25 could be explained by the behavior in polar nanoregions (PNRs), while the ferroelectric domains contribute to dipole polarization in BT. Relaxation in BT could be interpreted as successive change in polarization behavior from normal ferroelectrics to relaxor ferroelectric via DPT ferroelectrics.