(La2/3Ca1/3)(Mn(3-x)/3)Fex/3)O3体系磁电阻行为的研究

通过系统地测量（La_2/3Ca_1/3）（Mn_{（3-x）／3}Fe_x／3）O₃（x＝0、0.1、0．2、0．3的体系样品的电阻率-温度关系以及一定温度下磁电阻率与磁场的关系,发现随x的变化其磁电阻率峰和电阻率峰均发生位移,磁电阻率峰值增大,并伴生磁电阻率峰展宽效应．作者认为由于Fe的替代,引起体系中Mn³⁺／Mn⁴⁺比率及磁矩的变化,加之外场对磁有序结构的调制作用,从而影响了Mn³⁺－O^－Mn⁴⁺的双交换作用,最终导致磁电阻行为发生变化．     

Multicolor up-conversion emissions of Tm3+/Er3+/Yb3+ tri-doped YF3 phosphors

Tm3+/Er3+/Yb3+ tri-doped yttrium fluoride (YF3) phosphors were prepared by a facile hydrothermal method. X-ray topographic analysis found that the phosphors were crystallized products. Their sizes and morphologies were characterized by scanning electron microscopy (SEM, Hitachi S-4800), which indicated that most of the YF3 phosphors were hundreds of nanometers in size. Up-conversion (UC) spectra were recorded under 980-nm diode laser excitation at room temperature with a fluorescence spectrometer (Hitachi F-4500). Plenty of UC emissions of Tm3+ and Er3+ were observed from ultraviolet to red. For Tm3+ ions, a five-photon process (approximately 291 nm and approximately 347 nm), a four-photon process (approximately 362 nm and approximately 452 nm), and a three-photon process (approximately 475 nm) were identified in the UC spectra. The UC emissions from the Er3+ were: approximately 380 nm, approximately 408 nm, approximately 521 nm, approximately 537 nm, and approximately 652 nm. Therefore, cyan-white light can be observed by the naked eye at 980-nm excitation, even under low excitation power density. By comparing the UC spectra of the phosphors annealed at different temperatures, we found that the intensity of the UC luminescence increased as annealing temperature increased. Furthermore, the spectral dependencies on Tm3+ doped concentrations were studied. The energy transfer processes and fluorescence dynamics in the tri-doped system are currently being investigated.     

Sintering and piezoelectric properties of Pb(Ni1/3Sb2/3)O3-PbZrO3-PbTiO3 ceramics

The sintering and piezoelectric properties of Pb(Ni_1/3Sb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics have been investigated. When the powders contain 48 mol% PbTiO₃ and less than 10 mol% Pb(Ni_1/3Sb_2/3)O₃ followed by calcination at 850°C for 2 h, the calcine only contains the perovskite structure; but if the Pb(Ni_1/3Sb_2/3)O₃ content is between 12 mol% and 14 mol%, both tetragonal and rhombohedral phases are obtained. The composition of the morphotropic phase boundary(MPB) in the Pb(Ni_1/3Sb_2/3)O₃-PbZrO₃-PbTiO₃ system is Pb(Ni_1/3Sb_2/3)O₃ = 12 mol%, PbZrO₃ = 40 mol% and PbTiO₃ = 48 mol%. As the composition at the MPB is sintered at 1260°C and 1280°C for 2 h, respectively, the maximum density (7.8 g/cm³) is obtained. The SEM micrographs indicate that a decrease in porosity with increasing sintering temperature is attained at 1280°C, which is due to a decrease in the number and size of pores. When the sintering temperature is higher than 1280°C, the porosity increases due to PbO evaporation leading to an increase of the number of pore sites and in enlargement of the pore diameter. When the compact composition at MPB is sintered at 1280°C for 2 h, the planar coupling coefficient (K _p) and mechanical quality coefficient (Q _m) tend to approach the maximum (0.488) and minimum values (292.5), respectively.     

Intermediate Temperature Sintering of La-Modified Pb(Zn1/3Nb2/3)O3-PbZrO3-PbTiO3 Piezoelectric Ceramics

In order to realize the co-firing with Ag/Pd electrodes in multilayer devices, Pb(Zn1/3Nb2/3)1-,-yZrxTiyO3(0.25＜x＜0.35, 0.25＜y＜0.35) piezoelectric ceramics (hereafter designated PZN-PZT)modified by La2O3 has been prepared by conventional technique with sintering temperature from 1100℃ to 1140℃. X-ray diffraction patterns demonstrated that pure perovskite phase was obtained. Secondary electron image (SEI) showed that crystalline grains in ceramics were well grown. d33 of manufactured sample was as high as 560×10-12C/N. kp was about 0.61 and tgδabout 30×10-3. The existence of liquid phase examined by electron diffraction in PZN-PZT sample is beneficial to sintering of the ceramic.     

Upconversion luminescence properties of YF3:Yb3+, Er3+ nanoclusters

The synthesis, characterization, and spectroscopy of upconverting Yb3+/Er3+ codoped YF3 rod-like nanoclusters are presented. The YF3 nanoclusters were synthesized by a simple hydrothermal method. The clusters structure was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Under 978 nm laser excitation, stronger blue (4F(5/2) --> 4I(15/2) and 2p(3/2) --> 4I(11/2)) and green (4S(3/2), 2H(11/2) --> 4I(15/2)) upconversion luminescence were observed at 978 nm. The measured intensity of upconversion luminescence was different when pump power changed, which shows that the blue and green upconversion luminescence come from three-photon and two-photon energy transfer processes, respectively.     

Up-conversion fluorescence of Tm3+ and Gd3+ in Yb3+/Tm3+ co-doped Gd2O3 nanocrystals

Through a co-precipitation method Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were synthesized. After sintered at 900 degrees C for 1 h in air, the as-prepared Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were converted into Gd2O3:20%Yb3+, 1% Tm3+ nanocrystals. Crystalline phases, sizes, and morphologies of the two samples were characterized by X-ray diffraction and field emission scanning electron microscope. The up-conversion (UC) fluorescence spectra of the Gd2O3:20%Yb3+, 1%Tm3+ nanocrystals were recorded by using a fluorescence spectrophotometer with a 980 nm continuous wave laser diode as excitation source. The nanocrystals not only present characteristic blue and ultraviolet (UV) UC emissions of activated Tm3+, but also show UV UC emissions of host Gd3+. The experimental study suggests that the excitation power has great effects on UC fluorescence properties and the energy transfer from Tm3+ to Gd3+ is very efficient.     

Dielectric properties of Pb(Zn1/3, Nb2/3)O3 ceramics modified by Ba(Zn1/3, Nb2/3)O3 and BaTiO3

Dielectric properties of lead zinc niobate (PZN) ceramics modified by barium zinc niobate (BZN) and BaTiO₃ (BT) were investigated. By adding the modifier of BT and BZN, the stabilization of perovskite phase of PZN increased, but its Curie temperature decreased linearly with the amount of added modifier. Room temperature dielectric constant of PZN increased by addition of stabilizers up to 12 and 15 mol% of BZN and BT, respectively. The maximum room temperature dielectric constant was observed to be 7800 at 12 mol% of BZN, and 9800 at 15 mol% of BT, respectively.     

Relaxor behavior in Ba(Zn1/3Nb2/3)O3-PbTiO3 new solid solution

Relaxor behavior has been found in a new solid solution between complex perovskite Ba(Zn(1/3)Nb(2/3))O(3) (BZN) and ferroelectric PbTiO(3) (PT), prepared by solid state reactions. A strong dispersion of the maximum of dielectric permittivity (epsilon(')) appears around the temperature of T(m), which shifts toward higher temperatures with increasing frequency. The variation of T(m) with frequency follows the Vogel-Fulcher relationship. The variation of 1/epsilon(') with temperature above Tm deviates from the Curie-Weiss law, but satisfies a Lorentz-type function. The relaxor behavior becomes weaker upon increasing PT-content.     

Ultraviolet upconversion fluorescence of Er3+ in Yb3+/Er3+-codoped Gd2O3 nanotubes

Under 980 nm excitation, room-temperature ultraviolet (UV) upconversion (UC) emissions of Er3+ from the 4G(9/2), 2K(13/2), and 2P(3/2) states were observed in Gd2O3:Yb3+/Er3+ nanotubes, which were synthesized via a simple wet-chemical route at low temperature and ambient pressure followed by a subsequent heat treatment at 800 degrees C. The experimental results exhibited that these UV emissions came from four-photon UC processes. In the Gd2O3:Yb3+/Er3+ nanocrystals, the energy transfers (ETs) from Yb3+ to Er3+ played important roles in populating the high-energy states of Er3+ ions. This material provides a possible candidate for building UV compact solid-state lasers or fiber lasers.     

CH_3SiCl_3-BCl_3-H_2体系气相沉积的热力学计算

利用FactSage software软件进行热力学计算,获得了CH3SiCl3(MTS)-BCl3-H2体系在化学气相沉积环境中Si-B-C陶瓷的热力学产物图和相图。讨论了在高温(900～1100℃)、低压(2 kPa、5 kPa和12 kPa)条件下系统总压、温度和反应气体比例等参数对主要产物产率的影响。结果表明,在所研究的参数范围内,系统总压、温度和气体比例对B4C相的产率影响比较明显,而对SiC相的产率影响不明显。气体比例对C相的产率影响比较明显,温度和系统总压对C相的产率影响不明显。各参数的变化对主要气态产物(BHx、CxHy、SiClx等)的产率有一定程度的影响。稀释气体分压的增加有利于富B相的生成,MTS分压的增加有利于SiC的生成。     

Perovskite phase formation in the PbMg1/3Nb2/3 O3-PbZrO3-PbTiO3 system by the columbite route

The reaction mechanism of PbMg_1/3Nb_2/3O₃-PbZrO₃-PbTiO₃ (PMN-PZT) perovskite phase prepared by the columbite route has been studied in the temperature range from 600 to 800 °C. The effects of heating and cooling rate during the calcination of 3PbO +MgNb₂O₆+PZT powder mixtures have also been investigated. Nearly pure perovskite phase, 0.9 PMN-0.1 PZTsolid solution with no pyrochlore phase, as determined by X-ray diffraction, could be prepared at 800 °C for 2 H. From DTA/TGA, dilatometry and XRD data the reaction mechanism of PMN-PZT solid solution formation could be divided into three steps: (i) decomposition of columbite (MgNb₂O₆) by reacting with PbO at 350 to 600 °C (ii) the formation of a B-site-deficient pyrochlore phase Pb₂Nb_1.33Mg_0.17O_5.50 at close to 650 °C, and (iii) the formation of perovskite phase PMN-PZT solid solution from the reaction of Pb₂Nb_1.33Mg_0.17O_5.50 pyrochlore phase with MgO and PZT above 650 °C.     

Structural order in Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Nb2/3)O3 and Ba(Mg1/3Ta2/3)O3 microwave dielectric ceramics

The process and nature of structural ordering and the factors that influence them have been investigated in the microwave dielectric perovskites, barium zinc tantalate (BZT), barium zinc niobate (BZN), and barium magnesium tantalate (BMT), sintered at various temperatures. The samples were characterized mainly by X-ray powder diffraction and transmission electron microscopy. The results show that short-range 1 : 1 B-site order features strongly in the early stages of ordering in BZT and BZN, but it is extremely rare in BMT, for which most grains commence with 1 : 2 order. As sintering progresses, 1 : 1 order is replaced by 1 : 2 long-range order in BZT and by disorder in BZN. Orientational variants of the ordered domains within grains occur in similar numbers when order is fine-scale, but their distribution is less homogeneous in well-ordered samples. Local inhomogeneities in the degree of order within grains, which will affect dielectric properties, correlate with both residual non-stoichiometry and the presence of dislocations. Incompletely reacted starting materials which may persist to late stages of sintering can also strongly influence order. Anomalously large ordered domains at grain boundaries are attributed to grain-boundary migration accompanied by enhanced diffusion. The results indicate that with starting materials that are well-mixed and homogeneous at the nanoscale, tailoring of physical properties should be possible by controlling the type and degree of order through chemical composition. This revised version was published online in November 2006 with corrections to the Cover Date.     

Pb(Zn1/3Nb2/3)O3-Ba(Zn1/3Nb2/3)O3铁电陶瓷结构与性能的研究

采用固相反应的方法系统地研究了BZN稳定PZN基陶瓷的相结构与介电性能.随着BZN含量的增加,PZN-BZN陶瓷中钙钛矿相的稳定性增强,居里温度近似呈线性下降,室温介电常数和介质损耗随也显著降低,最小值分别为380和0.002.为获得100%钙钛矿结构的PZN基陶瓷所需BZN的最小用量为8mol%～10mol%,当BZN的mol%超过15mol%时,PZN基陶瓷中钙钛矿相所占的百分比不再受烧结工艺的影响,基本保持100%.1kHz时Pb0.9Ba0.1Zn1/3Nb2/3O3陶瓷的最大介电常数Kmax=8680,tgδ=0.02,相应的居里温度Tm为24℃.     

双掺杂稀土锰氧化物La2/3(Ca1/3Sr2/3)1/3MnO3薄膜的输运特性

采用射频磁控溅射法制备了Ca、Sr双掺杂La2/3(Ca1/3Sr2/3)1/3MnO3(LCSMO)薄膜。电阻率-温度特性表明,薄膜在387K时发生铁磁金属相-顺磁非导体相相变。同时测试了薄膜在180,230和280K温度下的伏安特性．表明所制备的薄膜具有自阻效应,并分析了产生该现象的原因。     

PbZrO3-CdTiO3 solid solutions

The structural, nonlinear optical, and dielectric properties of (1-x)PbZrO₃ ·xtCdTiO₃ solid solutions were studied. The phase relations in the composition rangesx = 0–0.3 and 0.85-1.0 were established. The results suggest that the ferrielectric ordering in CdTiO₃ persists up to 730 K.     

Spectroellipsometric studies of 0.9PbMg1/3Nb2/3O3-0.1PbTiO3 thin films

0.9PbMg_1/3Nb_2/3O₃-0.1PbTiO₃ (PMN-PT) films of different thickness, ranging from 75 to 450 nm, were prepared on La_0.5Sr_0.5MnO₃ (LSMO)-buffered LaAlO₃ (LAO) substrates by pulsed laser deposition (PLD). The structural properties of these films were characterized by X-ray diffraction. The –2 scans indicated that all the films have a pure perovskite phase containing no impurity. The - and -scans confirmed that all the films possess a heteroepitaxial relation of PMN-PT(1 0 0) LSMO(1 0 0) LAO(1 0 0) structure. The surface morphology and cross section of the films were examined by scanning electron microscopy (SEM). Their dielectric constants and the leakage currents were measured by an impedance analyzer and a leakage digital electrometer, respectively. Furthermore, spectroellipsometry (SE) was used to characterize the depth profile, refractive index, and microstructural inhomogeneities, including voids, microroughness of surface, and the electrode/film interface of these films. Based on these studies, the correlation between the electrode/film interface and the electrical properties of the films was discussed. Our results show that the ratio of the electrode/film interface thickness to the film thickness increases as the film thickness decreases. The increase in this ratio results in deterioration of the leakage current and dielectric constant of the films.     

Al3+离子替代La0.67Ca0.33MnO3体系的结构和输运行为研究

系统研究了Mn位替代的La0.67Ca0.33Mn1-xAlxO3体系的结构和输运特性.结果表明,随Al3+替代含量的增加,在整个替代范围内,晶胞体积表现出单调减小的规律.而体系的电阻率急剧增加,绝缘体-金属转变温度TIM向低温方向移动,且与Al3+替代含量存在线性关联.对少量Al3+替代含量,在T＞TIM的高温区域体系的输运特性满足热激活模型,在T＜TIM的低温区域满足金属输运行为.这种输运行为随Al3+替代的变化特征,可从Al3+离子对Mn3+-O2--Mn4+双交换通道的破坏和所导致的晶格畸变方面给予解释, Al3+替代改变了电子的局域环境,进而影响到体系的输运行为.     

Synthesis and luminescence properties of BaTiO3:RE (RE = Gd3+, Dy3+, Tb3+, Lu3+) phosphors

Gd³⁺, Dy³⁺, Tb³⁺ and Lu³⁺ doped BaTiO₃-based phosphors were synthesized with modified solid-state technique at 1000 °C. The optimization of reaction conditions were carried out by thermogravimetry and differential thermal analysis methods (DTA/TG). The reaction products obtained in an air atmosphere were characterized by X-ray powder diffraction (XRD). Surface and elemental analyses were performed by using an SEM instrument. The excitation and emission spectra were recorded by photoluminescence spectrophotometer (PL). The thermoluminescence (TL) properties of BaTiO₃ samples doped with Gd³⁺, Dy³⁺, Tb³⁺ and Lu³⁺ were investigated.     

溶液法CH3NH3PbCl3单晶的生长与性能研究

分别采用蒸发结晶法和逆温结晶法生长尺寸约为4 mm×3 mm×3 mm的CH₃NH₃PbCl₃单晶。对两种方法生长的单晶粉体的XRD分析结果显示, 单晶具有立方晶系结构, 其晶格常数分别为0.56833、0.56891 nm。实验测量了CH₃NH₃PbCl₃单晶的红外光谱(FT-IR)和拉曼光谱, 并对谱峰进行了指认; 使用UV-VIS-NIR分光光度计、荧光光度计对CH₃NH₃PbCl₃单晶的光学性能进行了测试。结果表明: CH₃NH₃PbCl₃晶体的吸收边约为423 nm, 光致发光峰为433 nm, 带隙值为2.97 eV, 与CH₃NH₃PbCl₃薄膜的光学特性相比, CH₃NH₃PbCl₃单晶更具潜在的应用前景。最后, 结合第一性原理研究了CH₃NH₃PbCl₃晶体的能带结构, 计算得出带隙值2.428 eV, 与实验值吻合较好。     

Effective electroelastic moduli of 3-3(0-3) piezocomposites

In a high volume fraction particle-loaded piezocomposite, some ferroelectric particles appear to be in contact, as in a 3-3 connectivity material; others are isolated in the polymer matrix, as in a pure 0-3 connectivity material. Such a material can be considered as a composite of composites characterized by a 3-3(0-3) connectivity. This paper follows two others that have described a matrix method to calculate all of the effective parameters of pure 0-3 and 3-3 connectivity piezocomposites. These previous models are used to obtain the effective properties of a 3-3(0-3) composite. A proportion of 0-3 connectivity in the composite is introduced, and the effective properties are studied as a function of this proportion. Experimental results compared with these predictions show that the model allows an evaluation of the proportion of 0-3 connectivity through the analysis of the electromechanical performance of the composite samples.