片式陶瓷电容器技术的新进展

电子设备表面安装技术（ＳＭＴ）和小型化的进展，促使电子元件包括陶瓷电容器的片式化率不断提高，尺寸不断缩小。提高瓷料的介电常数，减小介质层的厚度，保持电极可靠的接触及降低瓷料的焙烧温度是当前的主要研究课题。同时为了提高电容器的性能．要求改进瓷料的热稳定性；为了降低电容器的成本，需要采用贱金属电极。本文从这几方面叙述了目前世界上的进展情况，并指出了其发展趋势。     

弛豫铁电单晶的多功能特性及其器件应用

以Pb(Mg1/3 Nb2/3)O3-PbTiO3(PMN-PT或PMNT)为代表的弛豫铁电单晶具有远高于常用锆钛酸铅Pb(Zrx Ti1-x)O3(PZT)陶瓷的压电性能,引起了基于新一代压电单晶的功能器件研究热潮.本研究团队在国际上率先利用Bridgman方法生长出了大尺寸、高质量PMN-PT等弛豫铁电单晶(d33...     

铅基复合钙钛矿型弛豫铁电单晶的生长基元与生长机理: II.成 分、结构起伏与 同型生长基元的分异和组装

铅基复合钙钛矿型弛豫铁电单晶体PMNT,PZNT的生长基元为多种[BO~6]配位八面体。这些同型生长基元受本身稳定性的制约而在熔体中存在的几率不同。相对于[MgO~6]^1^0^-,[ZnO~6]^1^0^-八面体基元来说,[NbO~6]^7^-,[TiO~6]^8^-是更为有利的八面体基元。在基元组装过程中,各种[BO~6]八面体基元在稳定性、尺寸大小与电价上的分异致使生长界面对基元有一定的选择性,从而造成了晶体生长时成分与结构的短程起伏,并为有序畴及其它化学缺陷团簇的形成提供了条件。当加入掺质PbTiO~3时,由于[TiO~6]^8^-与[NbO~6]^7^-两种基元在组装时的类聚性及[TiO~6]^8^-对晶体稳定性的贡献,晶体的微区成分与结构得以调制,焦发石相得以抑制,这构成了用Bridgman法能直接从熔体中生长出纯钙钛矿相PMNT单晶的基础。而[MgO~6]^1^0^-与[ZnO~6]^1^0^-八面体基元的差致使PMNT,PZNT两单晶的生长难度有别,这在选择合适的生长方法时需加以考虑。     

新铌酸盐Sr5NdTi3Nb7O30的合成与介电特性

一些铁电铌酸盐具有优良的电光性能和非线性光学性能,因此该类化合物的人工合成、结构与性能的研究受到了重视,其中钨青铜结构的系列晶体(例如SBN、KNSBN、SCNN)在材料的制备和器件的设计方面都取得了很大进展,它们在实时全息存储、集成     

Ce掺杂BNBT压电陶瓷的介电弛豫特性

研究了CeO2掺杂对(Na0.5Bi0.5)0.94Ba0.06TiO3(BNBT)陶瓷晶体结构、介电性能与介电弛豫行为的影响。XRD分析表明,在所研究的组成范围内陶瓷均能形成纯钙钛矿固溶体。修正的居里-外斯公式较好的描述了陶瓷弥散相变特征,弥散指数随CeO2掺杂量的增加而下降。掺杂量较低的陶瓷仅在低温介电反常峰Tf附近表现出明显的频率依赖性,随掺杂量的增加,陶瓷材料在Tf的介电反常峰和频率依赖性慢慢消失。根据宏畴-微畴转变理论探讨了该体系陶瓷介电弛豫特性的机理。     

Raman spectra and anomalies of dielectric properties and thermal expansion of lead-free (1−x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0, 0.08 and 0.1) ceramics

ABSTRACT

Thermal expansion, Raman and dielectric properties of the lead-free (1?x)Na_0.5Bi_0.5TiO₃-xSrTiO₃ (x = 0, 0.08 and 0.1) ceramic solid solutions, fabricated by the conventional solid-state reaction method, were investigated. The Sr-doping results in an increase of the dielectric permittivity, broadening of the permittivity maximum, enhancement of the relaxation near depolarization temperature, broadening of the Raman bands and shift of all anomalies toward lower temperatures. The observed effects are attributed to an increase of the degree of cationic disorder and enhancement of the relaxor-like features. Anomalies in the thermal expansion strain were observed at the temperatures corresponding to the dielectric anomalies but not related to any phase transitions. These anomalies are supposed to follow changes of the averaged unit cell volume in the temperature interval of tetragonal and rhombohedral phase coexistence.     

Second harmonic generation and dielectric study of the fine and coarse grain PMN-35PT ceramics

We investigated the grain size effect on the high temperature behaviour of PMN-35PT ceramics around the tetragonal–cubic phase transition using second harmonic generation (SHG) and dielectric spectroscopy. Our data revealed coexistence of the first-order ferroelectric phase transition and relaxor behaviour in the coarse grain (grain size ～4 µm) µ_PMN-35PT. The phase transition is hindered and relaxor features prevail in the fine grain (grain size ～150 nm) n_PMN-35PT ceramics. Effect of the grain-size reduction on the SHG and dielectric response could be attributed to stabilisation of intermediate domain configurations between the frozen polar nanoclusters and large ferroelectric domains and to the enhanced stability of polar nanoclusters in the fine grain ceramics.     

Elastic–plastic deformation of Pb(Zn1/3Nb2/3)O3–(6–7)% PbTiO3 single crystals during nanoindentation

The elastic–plastic deformation behavior of (001)- and (011)-oriented single crystal solid solutions of Pb(Zn_1/3Nb_2/3)O₃–(6–7)% PbTiO₃ (PZN–PT) have been studied using a nanoindentation technique. A procedure is presented here to isolate the elastic, elastic–plastic and plastic contributions to the deformation using the unloading data, and a parameter, referred to as relaxation, is defined to characterize the elastic–plastic deformation during nanoindentations. This relaxation parameter increases with the maximum indentation load due to the higher indentation stress induced, and it also causes less recovery of the material upon indentation unloading compared to predicted pure elastic recovery. For a (001) surface, the relaxation value remains virtually unchanged within the range of the maximum indentation load of 10–50 mN, possibly due to a complete localized depoling of the non-180° domain switching. It is also found that the unpoled surface is more prone to stress-induced depolarization compared to the poled surfaces. Furthermore, by applying the continuous stiffness measurement (CSM) technique, the effects of multiple loading/unloading are studied for both (001)- and (011)-oriented PZN–PTs using the maximum indentation loads of 20 and 50 mN. With more loading/unloading cycles at higher CSM frequencies, stress-induced depolarization becomes prevalent and the contribution of the domain reorientation towards elastic recovery is significantly reduced. As a consequence, the relaxation value is increased, indicating more elastic–plastic deformation. This CSM effect is especially pronounced for poled (011) surfaces.