Kojima Seiji, Aftabuzzaman Md, Dec Jan, Kleemann Wolfgang
Division of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan.
Department of Physics, Pabna University of Science and Technology, Pabna 6600, Bangladesh.
Materials (Basel). 2023 Mar 21;16(6):2502. doi: 10.3390/ma16062502.
Uniaxial ferroelectrics with tetragonal tungsten bronze structure are important functional materials with photorefractive, electrooptic, piezoelectric, and pyroelectric properties. SrBaNbO (SBN100) with > 50 is known as a typical uniaxial relaxor ferroelectric, while CaBaNbO (CBN100) undergoes nearly normal ferroelectric phase transitions. Single crystals of CSBN100 = [(CBN28) + (1 - ) (SBN61)] = CaBaNbO + (1 - ) SrBaNbO with nominal = 0.00, 0.25, 0.50, 0.75, and 1.00 were studied to clarify the dynamical properties at the crossover from relaxor ( = 0) to normal ( = 1) ferroelectric behavior. The longitudinal acoustic (LA) and transverse acoustic (TA) modes and a central peak (CP) related to the relaxation process of polarization fluctuations along the polar -axis were studied in uniaxial ferroelectric CSBN single crystals as a function of temperature via Brillouin scattering spectroscopy. A CBN28 ( = 1.00) crystal shows the sharp elastic anomaly of the LA mode in the gigahertz range toward Curie temperature, . However, those of CSBN25 ( = 0.25) and SBN61 ( = 0.00) crystals show diffusive anomalies due to stronger random fields. The relaxation time determined from the width of a CP shows a critical slowing down in the vicinity of . The elastic anomaly and slowing down of relaxation time of CSBN100 crystals become diffusive in the vicinity of as the CBN28 content decreases. The origin of the crossover from relaxor to normal ferroelectric phase transitions is discussed in terms of the difference in the A1 and A2 sites' occupancies.
具有四方钨青铜结构的单轴铁电体是一类重要的功能材料，具有光折变、电光、压电和热释电等特性。铌酸锶钡（SBN100），其中 ＞50，是一种典型的单轴弛豫铁电体，而铌酸钙钡（CBN100）经历近乎正常的铁电相变。研究了名义组成为 = 0.00、0.25、0.50、0.75 和 1.00 的 CSBN100 = [(CBN28) + (1 - ) (SBN61)] = 铌酸钙钡 + (1 - ) 铌酸锶钡单晶，以阐明从弛豫（ = 0）到正常（ = 1）铁电行为转变过程中的动力学性质。通过布里渊散射光谱研究了单轴铁电 CSBN 单晶中与沿极轴极化涨落弛豫过程相关的纵向声学（LA）和横向声学（TA）模式以及一个中心峰（CP）随温度的变化。CBN28（ = 1.00）晶体在吉赫兹范围内朝向居里温度 显示出 LA 模式的尖锐弹性异常。然而，CSBN25（ = 0.25）和 SBN61（ = 0.00）晶体的弹性异常由于更强的随机场而表现为弥散性异常。由 CP 宽度确定的弛豫时间在 附近显示出临界慢化。随着 CBN28 含量的降低，CSBN100 晶体的弹性异常和弛豫时间的慢化在 附近变得弥散。从 A1 和 A2 位点占有率的差异角度讨论了从弛豫铁电相转变到正常铁电相转变的起源。
