Ba1－xSrxTiO3的Sol-gel法制备与结构相变研究

采用sol-gel法制备了钛酸锶钡(Ba1－xSrxTiO3)．用XRD、DSC、Raman等表征技术研究了Ba1－xSrxTiO3的晶体结构和相变行为.结果表明,随着锶含量的增加,晶胞体积逐渐减小,c/a趋近于1,相变温度降低,相变热减少,相变弥散性增强,且存在热滞现象.Raman光谱发生有趣变化,当x=0.30时,室温下发生结构相变, Ba1－xSrxTiO3以立方相为主要存在相,相变具有有序-无序特征.     

钛酸铅和钛酸钡振动性质及铁电相变的密度泛函理论研究

采用密度泛函赝势的方法, 研究了不同晶相的钛酸铅和钛酸钡的振动模式. 没有发现钛酸铅存在低温相变的证据, 而钛酸钡则存在四方-正交和正交-三角铁电相变. 振动频率随四方应变的变化关系表明, 随着四方应变的增大, 软模的频率增大, 在某一个临界点, 不稳定的软模转变为稳定的振模. 由于钛酸铅具有较大的四方应变, 使得其能够在四方相稳定下来, 而钛酸钡较小的四方应变是其仍能够发生低温铁电相变的一个重要原因.     

亚微米级四方相钛酸钡低温固相法制备及晶型控制

以八水合氢氧化钡和α-钛酸为原料,在相对低的焙烧温度下,制备出近似球形、亚微米级的钛酸钡。通过XRD、SEM、Raman和FTIR等手段对钛酸钡样品进行表征,样品具有高结晶度,颗粒均一性良好。晶型转变的初步探究表明,立方相为主的钛酸钡可以在400℃发生晶相转变,成为以四方相为主的钛酸钡。     

不同Ti/Ba比钛酸钡纳米粉体及其陶瓷的制备和介电性能研究

采用溶胶-凝胶(Sol-gel)法制备了不同Ti/Ba比的钛酸钡纳米粉体及其陶瓷。通过XRD、SEM和TEM对钛酸钡粉体及陶瓷进行了表征,并测试了陶瓷的介电性能,研究了Ti/Ba比对陶瓷微观结构和介电性能的影响。结果表明:通过溶胶-凝胶工艺制备的纳米粉体主要为立方相钛酸钡,平均粒径约19~33 nm:随Ti/Ba比的增加,钛酸钡纳米粉体平均粒径呈先稍递减后增大的趋势,当粉体平均粒径大于30 nm吋,四方相在混合相中所占比例逐渐增大;Ti/Ba=1.01~1.03时,陶瓷中异常长大的晶粒较多,室温介电常数降低;1300℃烧结2 h的Ti/Ba=1.04的钛酸钡陶瓷具有较好的介电性能。     

铈锆氧化物纳米粉的合成及催化性能研究

采用改进的高分子凝胶法在较低温度下合成了铈锆氧化物固溶体Ce1-xZrxO2.这种合成方法对于合成亚稳相的复合氧化物是独特而有效的.XRD分析表明,当x=0～0.6时,固溶体为立方相结构;当x=0.7～0.9时,固溶体具有四方相结构;晶胞体积随x的增大呈线性减小;固溶体在1000 ℃以下具有稳定的相结构.从透射电镜图可以看出,产物的粒径在10～20 nm之间.TPR实验显示,当CeO2的摩尔含量为40%～60%时,铈锆氧化物固溶体的催化活性最好.     

弛豫基铁电单晶0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3的制备与 性能研究

用改进的Bridgman法,在加入助熔剂的条件下,生长出最大尺寸为φ30×25mm^3的铌锌酸铅-钛酸铅固溶体单晶[0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3]。无宏观缺陷的晶片的典型尺寸为20×15mm^2。晶体的单晶性及其结构用X射线衍射法加以研究。所得晶体用Laue衍射法定向,取(001)晶片进行性能表征。研究了材料的介电性能,并用偏光显微镜观察了(001)晶片的电畴结构。结果表明,室温下材料的介电常数较大,为2500～5000。随着温度的升高,材料发生四方铁电相—立方顺电相的相变,相变温度为190℃左右。单晶的介电温谱呈现明显的频率色钐现象,同时,介电常数最大值的温度tm随着频率的升高而降低,观察到了电畴结构的不均匀与孪生现象。     

溶胶-凝胶法制备的纳米PrOy-ZrO2固溶体的表层和体相结构

用改进的柠檬酸溶胶-凝胶法制备了纳米PrOy-ZrO2固溶体. 采用XRD, Raman和TEM等技术对纳米PrOy-ZrO2进行了表征. 结果表明, 改进的柠檬酸溶胶-凝胶法制备的PrOy-ZrO2固溶体于650 ℃焙烧后晶粒大小在5~10 nm之间; 于950 ℃焙烧(Pr>16%)后晶粒大小在20 nm左右. Pr能有效地使ZrO2稳定在四方或立方晶相. 随Pr含量的增加, PrOy-ZrO2固溶体的物相结构从单斜相逐步向四方和立方相转变. XRD和Raman得到的物相结构的差别表明, PrOy-ZrO2固溶体表层和体相结构存在不一致性, 随Pr含量增加, 体相逐步按照m→t→c的物相转变, 表层按照m→t→t"的物相转变. 表层更易生成低对称性和无序结构.     

纳米块体金属钆和镝的磁性相变分析

对纳米晶钆(Gd)和镝(Dy)块体材料的磁性进行了研究.与多晶比较,通常纳米晶的磁化强度减小,居里温度TC降低,但平均粒径为10 nm的纳米晶Dy的居里温度TC反而升高到100 K,平均粒径为10 nm的纳米晶Gd中还存在明显的反铁磁相.通过RKKY交换作用的计算知道,晶面晶界处原子的交换积分会发生正负号的变化,能量最低的稳定状态对应三种有序相:铁磁相、反铁磁相和扇相,晶粒中在一定条件下出现三相共存.对于平均粒径为10 nm的纳米晶,晶面晶界处原子所占比例很大,三相叠加的结果,对于Gd,即是在相变点附近出现磁化强度尖峰;对于Dy,则是磁化强度随温度升高下降缓慢,表现为居里温度TC比多晶升高.     

Ba_(1-x)Ca_xZr_(0.2)Ti_(0.8)O_3陶瓷的微观结构、相变与介电性质（英文）

采用传统的水热合成法和烧结过程制备了Ba_(1-x)Ca_xZr_(0.2)Ti_(0.8)O_3(BCZT,x=0.1,0.2,0.3)陶瓷.研究了Ca~(2+)含量对其相组成、微观结构和介电性质所产生的影响.结果表明当x=0.3时,出现了不纯相.随着Ca~(2+)含量的增加,BCZT陶瓷的形貌从平板状转化为不规则的立方体状.介电常数曲线显示为大而宽的峰,其峰值出现在约66℃.从介电损耗曲线可以观察到随着烧结温度的增加,出现了斜方相至四方相(T_(O-T))和四方相至立方相(T_(T-C))的多晶相变.     

导电ZrO_2复合纳米材料的制备和表征

用溶胶-凝胶方法,结合后焙烧处理,得到系列ZrO_2纳米材料及其与碳膜组成 的复合材料,XRD,Raman,SEM及电电性能测试表明：复合ZrO_2纳米材料有较小的 粒径（6.85 nm）,晶型为立方相,有较均匀的二次粒子分布,其中碳以碳膜形式 存在,复合材料有好的导电性能。将碳膜在823K氧化后,立方相转化为四方体相, 粒径增加,无导电性能。     

Y掺杂Ba0.90Sr0.08Ca0.02TiO3固溶体纳米晶粒尺寸 对其晶体结构的影响

The title nanocrystalline powders were prepared by sol-gel method, the influences of grain size on crystal structure were investigated by XRD and DSC techniques.The experiment results show that the tetragonal ferroelectric phase content of the powders and the Curie temperature Tc are increased with the increase of grain size.When the grain size is less than 34.7nm, crystal structure of the particle changes into cubic paraelectric phase and the transition of ferro-paraelectric phase disappears as well.     

Y掺杂Ba0.90 Sr0.08 Ca0.02 TiO3固溶体纳米晶粒尺寸对其晶体结构的影响

随着电子陶瓷材料向精细、微型、多功能化的方向发展，陶瓷用的粉体晶粒尺寸对物性影响的研究显得越来越重要。钡系钙钛矿结构铁电材料是应用极为广泛的电子陶瓷材料，其铁电性与晶粒尺寸密切相关，尤其是达到纳米级时，可使材料性质发生奇异变化。迄今人们仅对纯ＢａＴｉＯ３超微细粒子的晶粒尺寸对铁电相变的影响进行了研究［１～３］，对稀土钇掺杂Ｂａ（１－ｘ－ｙ）ＳｒｘＣａｙＴｉＯ３固溶体纳米晶的相关研究报道尚少，而铁电尺寸效应对这类电子功能材料的研究、开发起着关键作用。因此，开展这方面的研究具有重要的学术价值和实际意…     

Crystal structure and the paraelectric-to-ferroelectric phase transition of nanoscale BaTiO3

We have investigated the paraelectric-to-ferroelectric phase transition of various sizes of nanocrystalline barium titanate (BaTiO3) by using temperature-dependent Raman spectroscopy and powder X-ray diffraction (XRD). Synchrotron X-ray scattering has been used to elucidate the room temperature structures of particles of different sizes by using both Rietveld refinement and pair distribution function (PDF) analysis. We observe the ferroelectric tetragonal phase even for the smallest particles at 26 nm. By using temperature-dependent Raman spectroscopy and XRD, we find that the phase transition is diffuse in temperature for the smaller particles, in contrast to the sharp transition that is found for the bulk sample. However, the actual transition temperature is almost unchanged. Rietveld and PDF analyses suggest increased distortions with decreasing particle size, albeit in conjunction with a tendency to a cubic average structure. These results suggest that although structural distortions are robust to changes in particle size, what is affected is the coherency of the distortions, which is decreased in the smaller particles.     

Phase stabilization in nitrogen-implanted nanocrystalline cubic zirconia

The phase stability of nanocrystallites with metastable crystal structures under ambient conditions is usually attributed to their small grain size. It remains a challenging problem to maintain such phase integrity of these nanomaterials when their crystallite sizes become larger. Here we report an experimental-modelling approach to study the roles of nitrogen dopants in the formation and stabilization of cubic ZrO(2) nanocrystalline films. Mixed nitrogen and argon ion beam assisted deposition (IBAD) was applied to produce nitrogen-implanted cubic ZrO(2) nanocrystallites with grain sizes of 8-13 nm. Upon thermal annealing, the atomic structure of these ZrO(2) films was observed to evolve from a cubic phase, to a tetragonal phase and then a monoclinic phase. Our X-ray absorption near edge structure study on the annealed samples together with first-principle modelling revealed the significance of the interstitial nitrogen in the phase stabilization of nitrogen implanted cubic ZrO(2) crystallites via the soft mode hardening mechanism.     

Time‐Resolved Phase Transitions of the Nanocrystalline Cubic to Submicron Monoclinic Phase in Zirconia

The nanocrystalline cubic, tetragonal, and submicron monoclinic phases of pure zirconia were prepared by thermal decomposition of carbonate and hydroxide precursors. The crystallization and isothermal phase transformations of the oxide were studied using high temperature X‐ray diffraction, X‐ray diffraction and Raman spectra of quenched samples. Cubic zirconia formed first, and then progressively transformed to tetragonal and monoclinic phases at temperatures as low as 320°C. The cubic, tetragonal, and monoclinic phases for ZrO₂ were found to be distinct functions of crystallite size, indicating the nanocrystalline nature of these phases. They were found to exist within critical size ranges of 50 to 140 Å, 100 to 220 Å and 190 to 420 Å (±5 Å), respectively. Thus, as the crystallites grow during annealing, they first transform from cubic to tetragonal and then from tetragonal to monoclinic at critical sizes. The classical Avrami equation for nucleation and growth was applied to the tetragonal to monoclinic phase transition.     

新铌酸盐Ba5LnZnNb9O30(Ln=Y,La)的合成、结构与介电性能

在BaO-Ln2O3-ZnO-Nb2O5(Ln=Y,La)体系中通过固相反应法合成了填满型钨青铜结构的新铌酸盐Ba5YZnNb9O30与Ba5LaZnNb9O30.采用X射线衍射分析和扫描电镜进行了结构分析,并进行了介电性能测试.结果表明,Ba5YZnNb9O30为弛豫性铁电体,10kHz时的居里温度为25℃;室温时为四方钨青铜结构铁电相,晶胞参数a=1.25255(4)nm,c=0.39530(2)nm;1MHz时陶瓷体的室温相对介电常数为456.Ba5YZnNb9O30在室温下为四方钨青铜结构顺电相,晶胞参数a=1.25731(3)nm,c=0.39812(2)nm;频率为1MHz时,其陶瓷的室温相对介电常数为316.     

新铌酸盐Sr5LnTi3Nb7O30的结构与介电性能

在SrO-Ln2O3-TiO2-Nb2O5(Ln=La, Y)体系中,通过固相反应法，合成了填满型钨青铜结构新铌酸盐Sr5LaTi3Nb7O30与Sr5YTi3Nb7O30.分别采用X射线衍射分析、扫描电镜进行了结构分析,并进行了介电性能测试.结果表明, Sr5LaTi3Nb7O30室温时为四方钨青铜结构顺电相,晶胞参数a=1.233 60(4) nm, c=0.388 01(2) nm;频率为1 MHz时,其陶瓷的室温相对介电常数为466,介电损耗约为5×10－3.Sr5YTi3Nb7O30为弛豫性铁电体, 10 kHz时居里温度为260 ℃;室温时为四方钨青铜结构铁电相,晶胞参数a=1.228 80(4) nm, c=0.387 05(2) nm; 1 MHz时,陶瓷体的室温相对介电常数为290.     

新钽酸盐Ba3TiTa4O15的结构与介电性能

在BaO Ta2O5系统通过掺Ti4＋合成了新钽酸盐Ba3TiTa4O15,用粉晶XRD对其结构进行了分析,并测试了其烧结体的介电特性.结果表明:Ba3TiTa4O15在室温下属于填满型四方钨青铜结构,晶胞参数a=1.256 27(6)nm, c=0.395 86(4)nm; Ba3TiTa4O15在－35 ℃从铁电相转变为顺电相.     

新钽酸盐Ba2LnTi2Ta3O15(Ln=Y、La)的结构与介电性能

通过固相反应法合成了四方钨青铜结构新钽酸盐Ba2LaTi2Ta3O15与Ba2YTi2Ta3O15,分别进行了X射线衍射分析与介电性能测试.结果表明, Ba2LaTi2Ta3O15室温时晶胞参数为a=1.242 64(5) nm, c=0.391 57(2) nm,为四方钨青铜结构顺电相；Ba2YTi2Ta3O15室温时晶胞参数为a=1.236 46(4) nm, c=0.388 60(2) nm,为四方钨青铜结构铁电相,铁电相与顺电相转变温度为180 ℃.频率为1 MHz时, Ba2LaTi2Ta3O15陶瓷的室温相对介电常数为194,介电损耗也降低至8×10－4. Ba2YTi2Ta3O15陶瓷的室温相对介电常数为107.