反铁电晶体PbZrO3序参量和对称性的研究

在反铁电晶体锆酸铅(PbZrO3)顺电反铁电相变中,伴随有对称性的变化.前人工作中选择反极化参量(P)或子晶格的极化矢量(PA、PB)作为反铁电相的序参量,根据居里原理得出了反铁电晶体锆酸铅反铁电相对称性所属空间群为Pbam(D2h)或Pba2(C2v).但是通过对中子衍射实验结果分析,该晶体反铁电相对称性所属空间群不是Pbam(D2h)或Pba2(C2v),而是P2/m(C2i).本文选取轴矢量R作为反铁电相的序参量,对锆酸铅晶体应用居里原理,恰能得到正确的对称性P2/m(C2i).     

NH4H2PO4晶体反铁电相的对称性及序参量

在反铁电晶体NH4H2PO4(ADP)顺电反铁电相变中,对称性所属点群也随之发生相应的改变.通过对实验结果的分析,我们认为NH4H2PO4(ADP)晶体反铁电相对称性所属点群为P2(C2).选用轴矢量R作为序参量来描述NH4H2PO4(ADP)晶体反铁电相变中对称性的变化,应用居里原理,恰能得到NH4H2PO4(ADP)晶体反铁电相的正确对称性所属点群P2(C2).     

锆钛酸铅薄膜的溶胶-凝胶制备工艺及结构与物性的研究

采用溶胶-凝胶匀胶法制备锆钛酸铅铁电薄膜,研究了前驱体影响因素(如有机溶剂、前驱单体加入顺序、添加剂)、溶胶影响因素(如溶胶浓度、pH值)、匀胶速度和退火温度对成膜质量及薄膜微结构、铁电性的影响.结果表明:采用乙二醇甲醚为溶剂对pb2+、Zr4+和Ti4+金属盐进行溶解优于乙醇和乙二醇,但由于乙二醇甲醚对硝酸锆的溶解性差,对硝酸锆应先用乙醇溶解再加入乙二醇甲醚的方法来进行溶解;以硝酸锆为Zr源配制溶胶时,只有先将Pb前驱液滴加到Ti前驱液中,然后再滴入Zr前驱液的方式才能得到澄清前驱体.将锆钛酸铅溶胶浓度和pH值分别控制在0.2～0.3 mol/L和2～3较为适宜,与此溶胶相适应的匀胶参数:转速为4000 r/min,时间为60 s.随退火温度升高,薄膜的晶化程度增加,且逐渐表现出(100)晶面择优取向,晶格常数c和四方率c/a逐渐增加,而晶格常数a逐渐减小;随退火温度升高,晶粒尺寸逐渐增大,使得剩余极化强度逐渐增加,矫顽场强逐渐减小.当退火温度为850 ℃时制备的锆钛酸铅薄膜具有均匀的晶粒、较低的表面粗糙度和最为优异的铁电性.     

PZT基反铁电材料研究进展

在综述Pb(Zr,Ti)O3(PZT)基反铁电材料的研制与性能研究进展的基础上,重点探讨了PZT95/5反铁电材料和在PZT基础上掺杂改性的Pb(Zr,Sn,Ti)O3(PZST),(Pb,La)(Zr,Sn,Ti)O3 (PLZST)反铁电材料.总结了利用La3+、Nb4+、Hf4+、Sr2+、Ba2+和Nd3+等离子对富锆PZT以及PZST粉体、陶瓷以及薄膜材料的掺杂取代改性研究.讨论了各类PZT基反铁电材料的铁电(FE)-反铁电(AFE)相变机理以及其场致应变性能.展望了PZT基反铁电材料今后研究与应用的发展方向.     

四方相铌镁酸铅-钛酸铅单晶的声光特性研究

准同型相界附近的弛豫铁电单晶体具有较大的压电效应,因而得到了广泛地研究.一般而言,具有较大铁弹响应的材料也具有较高的声光效应.尤其是大的晶格参数变化和应力所致相变可以同时产生大的折射率变化,二者可以同时提高声光效应.本文在马赫-曾德尔干涉光路中对晶体样品施加单轴应力,测量得到了0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3(0.65PMN-0.35PT)单晶的声光系数π.研究结果表明,该单晶表现出了极高的声光系数,例如,π33达到了15.2×10-12 m2/N.这些研究结果表明,弛豫铁电单晶是激光束偏转器和声光调制器的优选材料.     

纳米级锆酸钐的合成工艺研究

采用L9(33)正交试验方案研究了溶液浓度、反应温度和pH值等三因素对共沉淀法制备锆酸钐粉体的影响.采用XRF、SEM等测试手段对纳米级锆酸钐粉的组分和形貌等进行表征,结果发现三因素对纳米级锆酸钐的组分有不同程度的影响:在共沉淀反应中,三因素相互作用,其中溶液浓度是影响其组分的主要因素;随着溶液浓度的升高,其组分差距增大,随着反应温度和pH值的升高,其组分差距表现出先增大后减小的趋势.当溶液浓度为0.6 mol/L、反应温度为50℃、pH值为10时为最佳制粉工艺,并在最佳工艺条件下制得了组分、形貌优良的纳米级锆酸钐粉.     

锗酸铅(Pb5Ge3O11)铁电单晶的生长与缺陷研究

采用坩埚下降法成功生长了铁电锗酸铅(Pb5Ce3O11)单晶.所用Pt坩埚尺寸为φ25mm × 200mm和φ10mm×60mi,炉温控制在高于熔点50～80℃,固液界面温度梯度小于25℃/cm,生长速率小于0.5mm/h.所得晶体呈浅棕色,最大尺寸达φ25mm×60mm.采用光学显微镜(OM)及电子探针(EPMA)研究了所得晶体的生长缺陷(气泡、包裹体等),讨论了产生这些缺陷的原因,提出了控制及减少此类缺陷的方法.     

Investigation of crystal lattice defects of PbZrO3 single crystals by transmission electron microscopy

The investigation of PbZrO₃ single crystal structure was carried out by the method of transmission electron microscopy (TEM). It is shown that extended planar defects, slip lines, twins, and morié patterns are observed in PbZrO₃.     

On the Symmetry of the n=1 Ruddlesden‐Popper Phase Ca2FeO3Cl

Single crystals of Ca₂FeO₃Cl have been obtained as a by product during single crystal growth experiments of calcium ferrates from a CaCl₂ flux. The reddish‐brown optically uni‐axial crystals adopt the tetragonal space group P4/nmm with a = 3.8381(4) Å and c = 13.685(2) Å and Z = 2 formula units per cell. The structure has been determined from a single crystal diffraction data set collected at room conditions and refined to final residual R(|F|) = 0.053 for 163 observed independent reflections with I > 2σ(I). Ca₂FeO₃Cl belongs to the structure family of the Ruddlesden‐Popper series with n = 1, which is also referred to as the K₂NiF₄‐type. Main building units are layers of perovskite type corner connected FeO₅Cl‐octahedra perpendicular to [001]. The two crystallographically independent calcium ions are located between the octahedral layers and are coordinated by nine ligands each: Ca1 (4×O + 5×Cl) and Ca2 (9×O). Following prior studies Ca₂FeO₃Cl crystallizes in space group P4. However, the present investigation shows clearly that this assignment is incorrect and that the compound has been described in an unnecessarily low symmetry.     

Bilayered Super-Structures of Antiferroelectric Mesogens

Abstract

Crystal structures of two antiferroelectric mesogens, TFMHPBC and MHPBC-10, were analysed by an X-ray diffraction method. In both crystals, mesogen molecules formed a herringbone structure which was essentially the same as that proposed for the antiferroelectric liquid crystal phase. Because of the crystallographic 2₁-symmetry along the b-axis, only the b-axis component of the dipole moment remains in a smectic layer. Since the dipole moment in the next layer has the same magnitude but the opposite direction, both crystals show no dipole moment as a whole. These structural features observed in their crystal states seem to be conserved in their antiferroelectric liquid crystal phases which are just above their crystal phases.     

Investigation of a Twisted Phase between the Cholesteric and the Smectic A Phase

In a ternary mixture of two liquid crystals and a non-mesomorphic chiral dopant an intermediate state with an unusual texture was found between the cholesteric and the S_A phase which could be identified as a separate twisted mesophase. The reflection wavelength of this mesophase does not change with temperature whereas the transmission of unpolarized light decreases from 50 to 20%. The experimental findings point to the existence of a twisted grain boundary phase.     

PbLa（ZrSnTi）O3弛豫反铁电单晶的畴结构与成畴机制

使用助熔剂法生长了PbLa(ZrSnTi)O3弛豫反铁电单晶,使用偏光显微镜对单晶中的畴进行了观察。结果表明,在(001)面上,PbLa(ZrSnTi)O3单晶中存在[110]走向和[110]走向的畴,以及[100]走向和[010]走向的亚畴。对PbLa(ZrSnTi)O3单晶的成畴机制进行了分析,引入微区应力成畴机制解释了单晶中[110]走向和[110]走向的畴结构,而对[100]走向和[010]走向的亚畴结构则要同时考虑极性微区中自发极化的影响。     

La3+掺杂对Pb(Lu1/2Nb1/2)O3反铁电单晶储能性能的影响

采用顶部籽晶法生长了La3+掺杂Pb(Lu1/2Nb1/2)O3(PLN)反铁电单晶,晶体组分简写为xLa-PLN(x=1;、3;、5;),并详细研究了La3+掺杂对PLN晶体储能性能的影响.通过ICP测试了不同配比晶体的实际掺杂比例,分别为0.3;、1.1;、2.9;.XRD显示该晶体体系为正交相钙钛矿结构,且存在两套超晶格衍射点阵,分别由A位铅离子反平行排列和B位离子有序排列导致.介电温谱给出了晶体的介电常数、介电损耗随温度和频率的变化规律,不存在弥散相变.变温电滞回线显示,该体系均表现出典型的双电滞回线特性,且随着La3+含量的增加,有效储能密度逐渐增大,最高储能密度达到5.1 J/cm3.这主要是由于La3+掺杂导致体系的容忍因子下降,从而增强了反铁电稳定性,最终提高了PLN体系的能量存储密度.     

Structure,Stability and Response to the Electric Field of Antiferroelectric Smectic Materials

Abstract

The structure and switching of five antiferroelectric mesogens are studied by the constant temperature-pressure molecular dynamics simulation. The conformations of the end chains in the smectic phase are compared with those at an isolated single molecule estimated by the method of molecular orbitals, where the bending angle of the chiral chain as well as the angle of the achiral one is shown to be enhanced. The tilt angles obtained here are in well agreement with the experimental ones. The response of the anticlinic alignment to the transverse electric field is also tested.     

Pb的过量值对溶胶-水热法合成钙钛矿型PZT反铁电陶瓷粉体的影响

采用溶胶-水热法合成了具有单一钙钛矿结构的PZT反铁电陶瓷粉体.根据课题组前期的实验结果,选取的水热反应温度为180℃,水热反应时间为24 h,矿化剂KOH的浓度为3 mol/L,探讨了Pb的过量值对合成PZT陶瓷粉体的影响.实验发现,Pb的过量值过低,不足以补偿反应过程中Pb的损失量,A位的Pb缺失易导致PZT粉体结晶度的下降,颗粒结晶不完整.随着Pb过量值的增加,颗粒结晶增强,结晶也越完整.当Pb过量增加到10;时,实验获得了结晶良好的PZT粉体.因此,本实验Pb的最佳过量值为10;.