Sol-Gel Derived Ferroelectric Thin Films: Avenues for Control of Microstructural and Electric Properties

The paper presents short review of the works performed during the last few years in the field of the alkoxy-derived ferroelectric films. PZT films were prepared using titanium and zirconium alkoxides and Pb(CH₃COO)₂· 2H₂O as precursors. Different way of lead acetate dehydration and the impact of lead excess in the precursor solutions on the properties of the PZT films are discussed. Trimetallic alkoxide systems Bi(OR)₃-Ta(OR)₅-ROH (R = Me, Et or ⁱ Pr) were studied as precursors for preparation of SrBi₂Ta₂O₉ films. Films prepared from these solutions and annealed at the temperature between 700 and 750°C demonstrated the remanent polarization P_r* – P^{^} _r = 7–9 C/cm². Ba_1-xSr_xTiO₃ films we applied from modified alkoxide solutions. Decomposition of the organic phase in the course of thermal treatment of the films is studied by IR-spectroscopy. The dependence of the dielectric permittivity of the films via the annealing temperature is reported. Preparation of LiNbO₃, SrZr_0.2Ti_0.8O₃, Zr_0.8Sn_0.2TiO₄ is briefly discussed.     

烘烤温度对溶胶-凝胶法制备镧掺杂钛酸铋薄膜结构与铁电性质的影响

采用溶胶-凝胶法，在保持薄膜结晶温度和有机物分解温度相同情况下，发现烘烤温度（即溶剂的挥发温度）对镧掺杂钛酸铋薄膜的晶体结构、表面形貌和铁电性质均产生重要影响.在较低烘烤温度下得到的薄膜（117）择优取向明显.但随着烘烤温度增加，薄膜的（117）择优取向逐渐减弱.薄膜的表面晶粒形貌则从棒状逐渐转变为盘状.还测量了薄膜的铁电性质，发现在250℃烘烤温度下得到的薄膜具有最大的剩余极化强度，2Pr为28.4μC/cm2.对实验现象进行了定性解释. 关键词： 溶胶-凝胶法 烘烤温度 铁电薄膜     

Improved microstructure, dielectric and ferroelectric properties of microwave-sintered Sr0.5Ba0.5Nb2O6

Ferroelectric strontium barium niobate (SBN) powder was synthesized by solid-state route. The green compacts were sintered in the temperature range 1250–1350 °C in a microwave furnace. The microstructural study, using SEM, revealed the grain size in the range 2–20 μm without microcracks, depending on the sintering temperature. This is in contrast to that obtained conventionally for sintered SBN powder synthesized by solid-state route, which resulted in duplex microstructure with microcracks [N.S. VanDamme, A.E. Sutherland, L. Jones, K. Bridger, S.R. Winzer, J. Am. Ceram. Soc. 74 (1991) 1785; P.K. Patro, A.R. Kulkarni, C.S. Harendranath, Ceram. Int. 30 (2004) 1405; P.K. Patro, Trans. Ind. Inst. Metals 59 (2006) 229]. Impedance analyzer and ferroelectric hysteresis loop tracer were used for the dielectric, ferroelectric, I–V and electric fatigue measurements. Microwave sintering also resulted in a dielectric maxima ε_max 2590 at 1 kHz (compared to 1103 for conventional sintering [P.K. Patro, A.R. Kulkarni, C.S. Harendranath, Ceram. Int. 30 (2004) 1405]) for the sintering temperature of 1350 °C. Similar improvement in microwave-sintered SBN was observed depending on their sintering condition. The origin of this difference is attributed to microstructural differences arising from difference in heating method. In this paper the observed dielectric and ferroelectric behavior have been correlated with different sintering conditions and consequent microstructure due to microwave sintering.     

四方铁电体PbFe0.5Nb0.5O3精细结构的第一性原理研究

采用全电势线性缀加平面波法(FPLAPW),计算了PbFe0.5Nb0.5O3的总能量,从而确定了它的四方铁电稳态结构,即B位离子(Fe和Nb)在四方铁电相的平衡构型.计算结果表明,Fe相对于氧八面体沿[001]方向的位移为0.022nm,而Nb的偏心位移为0.0020nm,其中铁电非稳性主要归因于前者 关键词： 铁电体 密度泛函理论 平面波法     

Electric field dependence of the Curie temperature and microwave absorption in displacive ferroelectrics with impurities

The electric field dependence of the complex dielectric constant in an anharmonic defect ferroelectric crystal is calculated in its paraelectric phase from the Silverman-Joseph-Hamiltonian augmented with fourth-order phonon coordinates using double-time Green’s functions. The field and impurity dependence of the shift in the Curie temperature is discussed. An expression is obtained for the electric field dependence of dielectric loss at microwave frequencies in defect ferroelectrics. An erratum to this article is available at .     

Sound velocity change in doped displacive ferroelectrics

An expression is obtained for the sound velocity change in doped displacive ferroelectrics, in the presence of an electric field by considering higher order anharmonic terms in the modified Silverman-Joseph Hamiltonian. The mass and force constant changes due to impurity may give cancellation effects. The presence of higher order anharmonicity decreases the sound velocity which in turn varies with the applied electric field. The sound velocity decreases anomalously near the Curie temperature.     

Correlation of acoustic and thermal anomalies in ferroelectric crystals

The Pippard-Janovec relations are derived for correlating the anomalous elastic coefficient and the anomalous specific heat near the phase transitions of ferroelectric crystals. These relations are verified in the case of ferroelectric triglycine selenate crystal.     

Electroluminescence in lead titanate single crystals

Electroluminescence in PbTiO₃ single crystals is studied with variation in applied electric field, frequency (20 Hz to 5 kHz) and temperature. The EL onset depends on the rate at which the dipole switches. Extremely sharp upward rising nature of the pulses of micro second duration suggest that there is a self maintained discharge in the dielectric due to secondaryγ _p mechanism. Frequency dependence of EL suggests that both the secondary mechanisms, viz. theγ _p andγ _i are active after the application of a high field and the critical field at which this occurs decreases with increase in the frequency of the applied voltage. Similarly the onset voltage decreases with increase in frequency. The temperature dependence of EL at the applied frequency of 50 Hz shows that the onset voltage is intimately connected with the coercive field of the crystal and it is minimum at the Curie point. The study suggests that EL occurs in the bulk and there is a breakdown in the dielectric due to an avalanche formation.     

含随机分布缺陷的多晶铁电材料的有效电弹性能

针对铁电材料含有随机分布缺陷以及微结构在外场作用下发生变化的特点,建立起一个细观统计力学模型,考虑到缺陷和酶极化转动之间的相互影响,利用细观力学方法－Eshelby等效夹杂法和Mori-Tanaka的平均理论,具体分析了所含缺陷以及外场对铁电材料有效电弹性能和模量的影响。针对BaTiO3铁电陶瓷的有效电弹性能与常数的预报结果表明了缺陷的存在将增强材料的压电性能。     

Growth and properties of ferroelectric potassium ferrocyanide trihydrate single crystals

Single crystals of potassium ferrocyanide trihydrate, K₄[Fe(CN)₆·3H₂O (KFCT), a ferroelectric material with Curie temperature 251K were grown in silica gel at room temperature for the first time by the solubility reduction method. Resorcinol and ethyl alcohol were used for the purpose of gel setting and supernatant liquid respectively. Optical and mechanical properties were studied for the grown crystal. The structure of the grown crystal was confirmed by X‐ray diffraction analysis. Fourier Transform Infrared (FTIR) and FT Raman spectral analysis of the crystalline samples reveal that the crystalline sample consist consists of all functional groups. Thermal analysis of the crystalline sample was performed by TGA and DTA methods. The Vicker's micro hardness value was measured for KFCT crystals. The square etch pits with a hopper‐like structure is an indicative of 2D nucleation mechanism. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)