Compositional variation in 0.65 PbMg2/3Nb1/3O3 ‐0.35 PbTiO3 single crystals grown by high temperature solution growth technique

Single crystals of lead magnesium niobate titanate, 0.65 PbMg_2/3Nb_1/3O₃ (PMN) ‐0.35PbTiO₃ (PT) were grown using flux method near morphotropic phase boundary (MPB) composition. The crystals grown at the centre of the platinum crucible were found to PT deficient compared to those grown near the walls of the crucibles. A variation of ∼3.8 mol% in PT concentration was found in the crystals grown at the wall and at the centre of the crucible. The difference in the chemical composition of crystals grown at the centre and the near the wall of the crucible was observed by X‐ray diffraction, EDXRF, dielectric and thermal measurements. The presence of PT rich and deficient crystals is explained in terms of the segregation coefficient of PT in PMN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

(Ba0.5Sr0.5)Nb2O6基玻璃添加对BiFeO3陶瓷多铁性能的影响

采用固相法制备BiFeO3-x[BSN-G](x=0～5.0wt;)陶瓷样品,研究添加不同量的BSN-G对BiFeO3陶瓷微观形貌,电性能及磁性能的影响.研究结果表明:BSN-G的加入使得陶瓷样品气孔率降低,致密度提高.随着x的增加,陶瓷的介电常数和介电损耗呈逐渐降低趋势,当x=5;时,样品在1 kHz频率下的介电损耗为0.003.此外,添加BSN-G使得BiFeO3陶瓷的漏导电流降低,x=5;的样品具有饱和的电滞回线,其饱和极化强度Ps为1.5 μC/cm2,漏导电流密度J为0.39×10-6 A/cm2.交流阻抗图谱分析表明随着x的增加,样品的电阻呈增大趋势.活化能Ea随x增加而依次降低,进一步说明其损耗呈逐渐降低趋势.随着x的增加,样品的磁性能得到一定改善.     

Ce3+在Ba2ZnB2O6中的晶体学格位及其发光性能研究

通过高温固相法合成了Ba2ZnB2O6∶Ce3+蓝色荧光粉.通过XRD、Rietveld结构精修、激发和发射光谱、荧光衰减曲线以及变温荧光光谱等,对荧光粉的晶体结构和发光性能进行了研究.结果表明:Ce3+的掺入并未对基质的晶格结构产生影响,在350 nm近紫外光激发下,Ba2ZnB2O6∶xCe3+的发射峰为位于430 nm的不对称的宽谱,最佳掺杂浓度为x=0.01,Ce3+在Ba2ZnB2O6晶格中占据Bal和Ba3两种格位,随掺杂浓度升高更倾向于占据Ba3位.Ce3+的择优占位使荧光粉的发光由蓝光向蓝绿色区域发生了明显的漂移.     

Nb2O5/Co2O3加入量对(Ba,Sr)TiO3基电容器陶瓷介电性能的影响

研究了Nb2O5/Co2O3加入量[质量分数,Nb/Co(摩尔比)=0.8]不同对(Ba,Sr)TiO3(Barium strontiumtitanate,BST)铁电电容器陶瓷介电性能的影响,得到不同Nb2O5/Co2O3加入量与BST陶瓷性能的关系。借助扫描电镜(SEM)和X射线衍射仪(XRD)研究不同Nb2O5/Co2O3加入量对BST陶瓷显微结构和物相的影响,探讨了Nb2O5/Co2O3加入量对BST陶瓷性能影响机理。结果表明:当Nb2O5/Co2O3加入量为1.0%时,可得到满足Y5V特性、介电常数为3934、介质损耗为2.6%综合性能好的BST陶瓷。Nb2O5/Co2O3加入量对BST陶瓷性能的影响是通过细晶化、压抑展宽居里峰、改善介电常数温度特性、减少介电常数、形成杂相、形成“晶核-晶壳”结构等进行。     

Investigation on birefringence property in uniaxial crystal (Ca0.28Ba0.72)0.75(Sr0.60Ba0.40)Nb2O6

The birefringence of (Ca_0.28Ba_0.72)_0.75(Sr_0.60Ba_0.40)Nb₂O₆ crystal is measured basing on polarization‐ extinction method and conoscopic interference method. Experimental results show that the birefringence in this crystal is up to 10^‐5, the natural birefringence in this crystal is (n_o ‐n_e) = 5.89 x 10^‐5 with the He‐Ne laser wavelength at 632.8nm and the birefringence grads with wavelength at 532nm is 5.68 x 10^‐5, which indicate the good optical homogeneity of this crystal. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth,optical and luminescence properties of (Ce,Sr)‐doped PrAlO3 single crystals

Using the micro‐pulling‐down method, (Ce,Sr)‐doped PrAlO₃ square‐shaped single crystals (4×4×12 mm) were grown. Structural parameters studied by X‐ray powder diffraction were consistent with R3m space group. Compositional homogeneity was checked with electron probe micro‐analysis and found quite uniform. Absorption spectra and luminescence characteristics under UV and X‐ray excitations were measured at room temperature with no Ce‐related emission appeared. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of Mn2+ doped calcium l‐tartrate crystals

Single crystals of Mn²⁺ doped calcium levo‐ tartrate tetrahydrate (CLTT) were grown by single diffusion gel growth technique in silica hydro‐gel media. The doping of Mn²⁺ was varied by mixing 0.001M, 0.005M, 0.01M, 0.05M, and 0.1M solutions of MnCl₂ with 1M CaCl₂ solution in equal volumes in the supernatant solutions. The actual amount of Mn²⁺ doping in CLTT crystals was estimated by ICP (Inductively Coupled Plasma) technique. The powder XRD of the samples suggested no significant change in the unit cell dimensions and the presence of any extra phase. The FT‐IR spectra indicated the presence of water molecule, O‐H bond, C‐O bond and carbonyl C=O bond. The EPR spectra confirmed the presence of Mn²⁺ ions in the crystals. The variation of the dielectric constant with temperature confirmed the earlier results of pure calcium tartrate crystals and indicated the ferroelectric nature of the doped crystals. As the amount of doping of Mn²⁺ increased the value of dielectric constant increased. The results are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

SnO2掺杂对(Ba0.85Ca0.15)(Ti0.9Zr0.1-xSnx)O3无铅压电陶瓷介电弛豫与电性能的影响

采用固相烧结法制备了(Ba0.85Ca0.15)(Ti09Zr0.1-xSnx) O3(BCZTS)无铅压电陶瓷.研究了不同含量SnO2(x=0,0.02,0.04,0.06,0.08)对BCZT无铅压电陶瓷相结构、压电性能、介电性能和铁电性能的影响,并利用XRD、SEM、准静态d33测试仪等表征样品.结果表明,所有样品均为单一钙钛矿结构.当掺杂x=0.02时,(Ba0.ss Ca0.1s)(Ti0.9 Zr0.1-xSnx) O3无铅压电陶瓷材料的综合性能优异:d33 =553 pC/N,kp=49;,εr～ 7474(l kHz),tanδ～1.5; (lkHz),Pr=6.06 μC/cm2,Ec=2 kV/cm,利用Curie-Weiss定律对该实验结果进行拟合,发现x=0.02的样品的介电弛豫特征更为明显.     

B2O3对6ST-4LA微波介质陶瓷结构与性能的影响

为降低0.6SrTiO3-0.4LaAlO3(简称6ST-4LA)微波介质陶瓷的烧结温度,采用固相反应法,研究了B2O3对其结构与性能的影响.结果表明:添加B2O3可有效地降低6ST-4LA陶瓷的烧结温度,由1550℃降至1450℃;主晶相仍为赝立方钙钛矿结构固溶体,但有第二相的出现,其含量随着B2O3添加量的增加先降低后升高.当B2O3添加量为0.50wt;在1450℃下烧结时,6ST-4LA陶瓷获得最佳微波介电性能:εr=44.46,Q·f=51127 GHz,τf=-2.3×106/℃.     

Self‐diffraction and edge enhanced effect in the photorefractive crystal (Ca0.28Ba0.72)0.75(Sr0.60Ba0.40)0.25Nb2O6

The optical properties based on Self‐diffraction phenomena and the edge enhanced of optical correlation pattern effect with a Ca²⁺‐doped (Ca_0.28Ba_0.72)_0.75(Sr_0.60Ba_0.40)_0.25Nb₂O₆ (CSBN₇₅) crystals and a He‐Ne laser at 632.8 nm are studied in this paper. The experimental results show that its practical application as photorefractive material is worth further investigation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impedance analysis and high temperature conduction mechanism of flux grown Pb(Zn1/3Nb2/3)0.91Ti0.09O3 single crystal

The electrical properties of Pb(Zn_1/3 Nb_2/3)_0.91Ti_0.09O₃ single crystals over a wide range of frequencies (20 Hz to 2 MHz) and temperature (30 to 490 °C) were studied using impedance spectroscopic technique. A strongly frequency dependant Debye type relaxation process in crystals was observed. The activation energy for relaxation was found to be 1.72 eV. The nature of Cole‐Cole plot reveals the contribution of only grain (bulk) effect in the sample. The temperature dependant conductivity was found to different in different temperature regions, which shows the presence of different carrier for conduction. The activation energy for conduction in the order of 1.69 eV suggested that the conduction process in higher temperature region is governed by the presence of lead vacancy defect in the sample. Further, the negative temperature thermistor behaviour of the system was explored and various associated parameters were calculated. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Structure of (Cr,Cu)(Sr,La)2(La,A)Cu2O8‐δ (1212‐type) and (Cr,Cu)Sr2(Y,Ce)2Cu2O10‐δ (1222‐type) Phases

Conditions of the synthesis, crystal structures, mechanical properties, electrical resistivities and magnetizations of cuprates with the general formula (Cr,Cu)(Sr,La)₂(La,A)Cu₂O_8‐δ where A=Ca or Sr of 1212‐type and (Cr,Cu)Sr₂(Y,Ce)₂Cu₂O_10‐δ of 1222‐type were investigated. The compositions of the cuprates and an amount of the impurity phases in the samples were determined. Rietveld refinement of the structure was carried out. It was found that the formal charges of Cu (FC_Cu) calculated from the electroneutrality of refined phase compositions do not achieve value optimal for the appearence of superconducting phases.     

Properties of Sm‐doped CaNb2O6 thin films deposited by radio‐frequency magnetron sputtering

Sm‐doped CaNb₂O₆ (CaNb₂O₆:Sm) phosphor thin films were prepared by radio‐frequency magnetron sputtering on sapphire substrates. The thin films were grown at several growth temperatures and subsequently annealed at 800 °C in air. The crystallinity, surface morphology, optical transmittance, and photoluminescence of the thin films were investigated by X‐ray diffraction, scanning electron microscopy, ultraviolet‐visible spectrophotometry, and fluorescence spectrophotometry, respectively. All of the thin films showed a main red emission radiated by the transition from the ⁴G_5/2 excited state to the ⁶H_9/2 ground state of the Sm³⁺ ions and several weak bands under ultraviolet excitation with a 279 nm wavelength. The optimum growth temperature for depositing the high‐quality CaNb₂O₆:Sm thin films, which was determined from the luminescence intensity, was found to be 400 °C, where the thin film exhibited an orthorhombic structure with a thickness of 370 nm, an average grain size of 220 nm, a band gap energy of 3.99 eV, and an average optical transmittance of 85.9%. These results indicate that the growth temperature plays an important role in controlling the emission intensity and optical band gap energy of CaNb₂O₆:Sm thin films.     

Dielectric constant,loss factor and ac conductivity of Ni2+‐doped K2ZnCl4 crystals in the ferroelectric‐commensurate,incommensurate and normal phases

The dielectric constant (ϵ), dielectric loss (tanδ) and ac conductivity (σ_ac) of virgin and thermally cycled undoped and Ni²⁺‐doped K₂ZnCl₄ (KZC) crystals in the ferroelectric‐commensurate (FC), incommensurate (IC) and normal phases (N) have been studied. Anomalous behaviour at the two‐phase transition points was observed while measuring ϵ along the polar a‐axis for the undoped sample. With increasing Ni²⁺concentration a systematic shift of the phase transition temperature towards lower values and a continuous inhibition of the peak height were detected. ϵ changed linearly with lnf up to f =10⁵ Hz. tanδ along the a‐axis declared the phase transitions by peak changes. After Ni²⁺‐doping this behaviour was preserved at the FC‐IC phase transition point while the IC‐N phase transition was manifested by a change in the slope of the straight line representing the tanδ‐T dependence. The ac conductivity changed lineally with frequency according to a relation of the form σ_ac = σ_o f ^β where 0>β>1.9. σ_ac increased monotonically with increasing temperature and doping concentration in the low‐temperature phases tending to merge in one straight‐line with high activation energy that might be due to superionic dc conduction in the high temperature N‐phase. Doping with Ni²⁺ pinned stripples, decreased the soliton‐soliton interaction, weakened discommensuration effects, shortened the IC‐phase and strongly affected the ‘chaotic' behaviour at the T_C‐IC. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Laser‐induced crystal growth of nonlinear optical Ba3Ti3O6(BO3)2 on glass surface

Nonlinear optical Ba₃Ti₃O₆(BO₃)₂ crystals were patterned on the surface of CuO (1 mol%)‐doped 40BaO‐40TiO₂‐20B₂O₃ glass by irradiations of continuous‐wave Nd:YAG (wavelength: λ=1064 nm) and Yb:YVO₄ (λ=1080 nm) lasers. Laser energies absorbed by Cu²⁺ ions were transferred to the lattice system through a nonradiative relaxation process, consequently heating the glass and inducing local crystallizations. For the lines patterned by Yb:YVO₄ laser irradiations with a power of 1 W and a scanning speed of 20 μm/s, a c‐axis orientation of Ba₃Ti₃O₆(BO₃)₂ crystals along the laser scanning direction is proposed from measurements of X‐ray diffraction analyses, polarized optical photographs, polarized micro‐Raman scattering spectra, and azimuthal dependence of second harmonic generations. The laser‐induced crystallization technique is found to be applied successfully for the spatially selective patterning of nonlinear optical Ba₃Ti₃O₆(BO₃)₂ crystals in glass. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electric‐field‐induced internal deformation in piezoelectric BiB3O6 crystals

For the first time electric‐field‐induced atomic displacements (internal strains) in non‐ferroelectric polar BiB₃O₆ single crystal plates (point symmetry 2) were investigated using X‐ray diffraction technique. The intensity variations of selected Bragg reflections were collected for three different orientations of the applied external electric field vector with respect to the crystal lattice and used for calculating the microscopic structural response of BiB₃O₆. Due to the limited number of the reflections providing measurable changes in Bragg intensities we restricted ourselves in analyzing the shift of the B₃O₆ sublattice relative to the Bi one. In addition, we considered the deformation of the Bi‐O, B(1)‐O and B(2)‐O bond lengths and identified the [B(2)O₃] group as the most sensitive structural unit to an external electric perturbation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electro‐optic,Piezoelectric and Dielectric Properties of Langasite (La3Ga5SiO14), Langanite (La3Ga5.5Nb0.5O14) and Langataite (La3Ga5.5Ta0.5O14)

Refractive indices were determined of single crystals of La₃Ga₅SiO₁₄ (langasite, LGS), La₃Ga_5.5Nb_0.5O₁₄ (langanite, LGN) and La₃Ga_5.5Ta_0.5O₁₄ (langataite, LGT) in the wavelength region between 0.36 μm and 2.33 μm. While phase‐matched optical second harmonic generation is not possible in LGS it occurs in the isotypic compounds LGN and LGT. Temperature‐dependent examination of the dielectric properties of LGS up to 600 °C showed anomalous behaviour. For all three substances the electro‐optic [r^σ_ijk] (“unclamped”) and the piezoelectric [d_ijk ] tensors were determined at room temperature. In addition, the temperature‐dependence of these properties was studied for LGS between –200 °C and +200 °C by a Jamin interferometer in combination with a modified Sénarmont compensator.     

Problems in the growth of Ce3+‐doped Li6Gd(BO3)3 crystals by Czochralski method

Cerium‐doped lithium gadolinium borate (Li₆Gd(BO₃)₃:Ce) single crystal has been grown by the Czochralski method. Some problems like macro defects and concave growth face were found. The macro defects are suggested to be caused by constitutional supercooling and concave growth face is caused by interface inversion. These problems can be resolved or eliminated through controlling the growth parameters strictly. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microwave dielectric properties of (1‐x)La(Mg0.5Sn0.5)O3‐x(Sr0.8Ca0.2)3Ti2O7 ceramic system with a near zero temperature coefficient of resonant frequency

In this study, the microwave dielectric properties of (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system prepared by the conventional solid‐state method have been investigated for application in mobile communication. It was found that the diffraction peaks of (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system shift to higher angles as x increases from 0.2 to 0.4. It was also found that the X‐ray diffraction patterns of the 0.8La(Mg_0.5Sn_0.5)O₃‐0.2(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramics exhibited no significant phase difference at different sintering temperatures. The average grain size of the (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system decreased from 6.4 to 4.3 μm as the value of x increased from 0.2 to 0.4 sintered at 1550 °C for 4 h. The dielectric constant increased from 26.6 to 35.9 and the quality factor (Q×f) decreased from 31,600 to 23,300 GHz for (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system as the x value increases from 0.2 to 0.4 sintered at 1550 °C for 4 h. The average value of temperature coefficient of resonant frequency (τ_f) increased from ‐18 to +8 ppm/ K as the x value increases from 0.2 to 0.4. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron irradiation‐induced effects on optical spectra of (NH4)2ZnCl4: x Sr2+ single crystals

The effect of electron‐beam irradiation with different doses on optical constants of (NH₄)₂ZnCl₄: x Sr²⁺ crystals with x=0.000, 0.020, 0.039, 0.087 or 0.144 wt% has been studied. The optical transmission in the energy range 3.4‐6.4 eV was measured hence the absorption coefficient was computed as a frequency function. The absorption coefficient was also calculated as a function of electron‐beam dose. Irradiation with e‐beam did not affect the allowed indirect type of transition responsible for interband transitions of (NH₄)₂ZnCl₄: x Sr²⁺ crystals. Values of the optical energy gap E_g and optical moment E_p for electronic interband transition of unexposed and (NH₄)₂ZnCl₄: x Sr²⁺ crystals after e‐beam exposure were deduced. The area under the absorption band at 5.30 eV was used to evaluate the effect of e‐irradiation on optical parameters of samples with x=0.00, 0.020 or 0.039. A shift in the position and a nonmonotonic change in the intensity of this band with increasing e‐beam dose was observed. Changes in the E_g value were used to evaluate the effect of e‐beam exposure dose on (NH₄)₂ZnCl₄: x Sr²⁺ samples with x=0.087 or 0.144. The obtained results were compared with those obtained for the same crystals after irradiation with different γ‐doses.