Flux growth and low temperature dielectric relaxation in piezoelectric Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals

Single crystals of Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT 91/9) have been grown by flux method after modifications in temperature profile, flux ratio and addition of excess ZnO/B₂O₃ which resulted in enhanced perovskite yield (more than 95%). Only a few crystals showed the presence of pyrochlore phase/variation in composition. A comparative characterization of these crystals were carried out in respect of piezoelectric charge coefficient d₃₃, dielectric constant, ac conductivity and hysteresis loop after cutting and poling the crystals along [001] direction. The total activation energy for conduction has been found to increase with Ti‐content in the sample. The effect of ZnO on growth behavior has been analyzed. A detailed analysis of PZNT (91:9) has been carried out at low temperature in respect of the various thermodynamic parameters related to the dielectric relaxation mechanism, like optical dielectric constant, static dielectric constant, free energy of activation for dipole relaxation, enthalpy of activation and relaxation time, have been calculated in the vicinity of transition temperature in the lower temperature region. The activation energy for relaxation at ‐10 and ‐49 °C have been found to be 0.09 and 0.02 eV respectively. The results were analyzed and a detailed dielectric analysis and low temperature relaxation behavior of PZNT crystals were interpreted. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

含NiTi阻挡层的硅基(La0.5Sr0.5)CoO3/Pb(Zr0.4Ti0.6)O3/(La0.5Sr0.5)CoO3铁电电容器异质结

应用磁控溅射法制备的非晶NiTi薄膜作阻挡层,在Si (100)衬底上构造了(La0.5Sr0.5)CoO3/ Pb(Zr0.4Ti0.6)O3/(La0.5Sr0.5)CoO3(LSCO/PZT/LSCO)铁电电容器异质结,研究了Pb(Zr0.4Ti0.6)O3铁电薄膜的结构和物理性能.实验发现LSCO/PZT/LSCO铁电电容器具有良好的电学性能,在417kV/cm的驱动场强下,PZT铁电电容器具有较低的矫顽场强(125kV/cm)和较高的剩余极化强度(19.0μC/cm2),良好电容-电压特性(C-V)和保持特性,铁电电容器经过1010次反转后,极化强度没有明显下降,表明了非晶NiTi薄膜可以用作高密度硅基铁电存储器的扩散阻挡层.     

Czochralski growth and characterization of Dy: La3Ga5.5Nb0.5O14 single crystals

Dysprosium (Dy) doped La₃Ga_5.5Nb_0.5O₁₄ single crystals were grown by the traditional Czochralski method along z‐axis. The structure of the crystal has been studied by X‐ray powder diffraction method, and the unit‐cell parameters are calculated to be a=8.22070 Å, c=5.12533 Å and V=299.965 ų. The segregation coefficient of Dy³⁺ in La₃Ga_5.5Nb_0.5O₁₄ crystal was measured by X‐ray fluorescence analysis. For 1 mol% doping level in the melt, the distribution coefficient of Dy³⁺ was determined to be 0.341 wt%. Specific heat, thermal expansion and transmission spectrum of Dy: La₃Ga_5.5Nb_0.5O₁₄ single crystals have been measured. The fluorescence spectra of Dy³⁺: La₃Ga_5.5Nb_0.5O₁₄ crystals were measured at room temperature, and there were four emission transitions occurring at 479, 576, 662 and 754 nm, respectively. The fluorescent lifetimes measurement results show 1.0% Dy: La₃Ga_5.5Nb_0.5O₁₄ possesses shorter fluorescence decay time (303.4 μs) than does 1.0%Dy:LGS (436.12 μs). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

以TiO2粉体为钛源水热合成Pb(Zr0.52Ti0.48)O3晶粒机理

用水热法合成了Pb(Zr0.52Ti0.48)O3(PZT)超细晶粒.通过对合成粉晶体的物相与晶体形貌的表征和对生成物中TiO2残余量的测定,初步分析了PZT粉晶粒形成的机理.在反应初期,随着温度的升高,TiO2粒子逐渐溶解.进入溶液的钛氧基团与溶液中的羟基相作用发生羟基化反应,形成钛的氢氧化物.钛与锆的氢氧化物相互作用,形成生长基元,它们与pb2+离子一起在PZT晶核生长界面上叠合、脱水、结晶,从而使PZT晶粒长大.     

Surface Chemical Bonding States and Ferroelectricity of Pb(Zr0.52Ti0.48)O3 Thin Films

The surface chemical bonding states and the ferroelectric properties of sol‐gel deposited lead zirconate titanate [Pb(Zr_0.52Ti_0.48)O₃, PZT] thin films coated on (111)Pt/Ti/SiO₂/Si substrates were investigated. X‐ray photoelectron spectroscopy (XPS) was used to determine the oxidation state of the surface and the chemical composition as a function of depth in ferroelectric PZT thin layers. Values for the dielectric constant and dissipation factor at 1 kHz for the 300 nm‐thick film were 1214 and 0.014 for the film annealed at 520 °C, and 881 and 0.015 for a film annealed at 670 °C. Measured values for the remanent polarization (P_r) and coercive field (E_c), from polarization‐electric field (P‐E) hysteresis loops biased at 10 V at a frequency of 100 Hz, were 16.7, 14.4 μC/cm² and 60, 41.7 kV/cm for 520 °C and 670 °C. The leakage current density (J) was 72 and 96 nA/cm² at an applied field of 100 kV/cm. It was found that the bonding states of lead and oxygen in the surface regions could be correlated with the ferroelectric properties of the integrated thin layers.     

Investigation on growth defects in Pb(Zn1/3Nb2/3)O3‐PbTiO3 crystals

Relaxor ferroelectric crystal (1‐x)Pb(Zn_1/3Nb_2/3)O₃‐xPbTiO₃ (PZNT) with x=0.07 (PZNT93/7) has been grown by the vertical Bridgman method from the high temperature solution of PZNT‐PbO system. The growth defects, such as nucleation core, inclusions, boundaries and particles, were investigated by optical microscope and scanning electron microscope. Sub‐structures were found in the flux inclusions and the lack of ZnO component in PZNT crystals was attributed to the existence of ZnO particles in the inclusions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

溅射制备不同厚度Pb(Zr0.52Ti0.48)O3薄膜结晶态的研究

研究了射频磁控溅射的Pb(Zr0.52Ti0.48)O3(PZT52/48)薄膜在退火晶化时,厚度对其结晶态及表面形貌的影响.首先利用Materials Studio软件对PZT分子进行了模拟,并模拟了X射线衍射(XRD)得到PZT的特征峰图;实验上,采用退火炉对不同厚度的PZT(52/48)薄膜进行了不同温度及时间的退火;接着采用XRD对各样片薄膜进行了结晶物相分析;采用FIB对部分样片薄膜表面形貌进行了观察.实验结果显示,薄膜的厚度及退火条件在一定程度上对其结晶态的影响是一致的;对于一定厚度的薄膜,合适且相同的退火(650 ℃)条件都可以使其形成单一的PZT(52/48)物相;二次退火对较厚薄膜结晶化有一定的作用,但随着溅射薄膜厚度的增加而累加了内应力,退火后形成有PZT(52/48)物相的较厚薄膜表面出现裂纹越明显.     

Role of oxygen vacancies in the coloration of 0.65Pb(Mg1/3Nb2/3)O3‐0.35PbTiO3 single crystals

The coloration and oxygen vacancies in 0.65Pb(Mg_1/3Nb_2/3)O₃‐0.35PbTiO₃ (PMN‐PT(65/35)) (starting composition) single crystals grown by a so‐called modified Bridgman technique were investigated in this paper. Light yellow and dark brown colored crystals were generally observed for the typical as‐grown PMN‐PT(65/35) single crystals. X‐ray diffraction results demonstrated that they were both of pure perovskite structure, but good electric properties were only obtained for the light yellow crystal. X‐ray photoelectron spectroscopy (XPS) was used to investigate the electronic structure of its components. The O 1s photoelectron spectra of the dark brown colored crystals located at the higher binding energy side, which meant the existence of the more oxygen vacancies. It accordingly led to the formation of the low valence cations associated with the coloration of the crystals, which is also testified by the obtained X‐ray photoelectron spectra of Ti and Nb. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on the growth and defects of La3Ga5SiO14 (LGS) crystals

New and high quality piezoelectric crystals La₃Ga₅SiO₁₄ (LGS) grown by the Czochralski method in a Platinum or Iridium crucible are reported in this paper. The growth defects in the LGS crystals were investigated by Transmission electron microscopy (TEM). It was found that cracks, inclusions, grain boundary and thermal stress in the LGS crystals. Their formation mechanisms and the method of eliminating these defects are discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

硅基(001)取向Pb(Mn1/3Nb2/3)O3-Pb(Zr,Ti)O3薄膜的制备及其铁电性能研究

采用磁控溅射法在LaNiO3/Si衬底上制备了6;Pb(Mn1/3Nb2/3)O3-94; Pb(Zr0.52 Ti0.48) O3 (PMnN-PZT)铁电薄膜,对其微结构和铁电特性进行了研究.结果表明,该铁电薄膜呈(001)高度择优取向,取向度高达98;.经过1010次铁电循环测试,铁电薄膜无疲劳现象;在104 s时间内,薄膜的铁电保持和印记特性稳定,无明显退化.该结果说明LaNiO3氧化物电极会降低PMnN-PZT薄膜的氧空位浓度,有效地缓解了电荷注入的问题,因此改善了PMnN-PZT薄膜的铁电性能.     

Pb0.92Sr0.08-xBax(Sb2/3Mn1/3)0.05Zr0.48Ti0.47O3的制备与性能研究

采用传统固相烧结法制备了Pb0.92Sr0.08-xBax(Sb2/3 Mn1/3)005Zr0.48Ti0.47O3(PSBSM-PZT)压电陶瓷样品.研究了不同Sr2+、Ba2+掺杂含量对样品的相结构、微观形貌、压电和介电性能的影响.结果显示:所有样品均为钙钛矿结构.而当x=0.02～0.06时,陶瓷样品组分位于准同型相界区(MPB).由于位于准同型相界区域的陶瓷样品对于电畴的转向具有促进作用,所以处于MPB区域的陶瓷样品具有较大的压电和介电性能,但同时由于电畴转向带来的较大内摩擦和结构损耗,从而提高了材料的机械损耗和介电损耗.当x=0.02时的陶瓷样品获得最佳的综合性能:d33=346 pC/N,kp=0.58,Qm=1217,εr=1724,tanδ=0.774;.     

An effective growth method to improve the homogeneity of relaxor ferroelectric single crystal Pb(In1/2Nb1/2)O3‐ Pb(Mg1/3Nb2/3)O3‐PbTiO3

Compositional segregation usually has negative effects on the growth of solid solution ferroelectric single crystals of Pb(In_1/2Nb_1/2)O₃‐Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ (abbr. PIN‐PMN‐PT or PIMNT). A modified Bridgman method was adopted in this work to control the segregation and improve the compositional homogeneity significantly. The characteristic of this work is to use multiround growths and gradient composition raw materials in order to keep the PbTiO₃ concentration constant during the crystal growth. As an example, the two‐round growth of ternary PIN‐PMN‐PT single crystal is conducted in the same Pt crucible with gradient raw materials, where the first‐round boule was used as the seed crystal for the second‐round growth. Our results show that the as‐grown (Ф80 mm × 270 mm) PIN‐PMN‐PT crystals exhibit higher phase transition temperatures (T_c∼180 °C, T_r/t∼110 °C) and larger coercive field (E_c∼5–5.5 kV/cm), which are much better than the performances of Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ crystals, and similar dielectric and piezoelectric performances (ε∼5000, tanδ∼1.25%, d₃₃∼1500 pC/N, k_t∼60%). And about 85 percent of the crystal boule grown by the two‐round growth technique could maintain its compositions around the morphotropic phase boundary.     

Growth of polar axis oriented tetragonal Pb(Zr,Ti)O3 films on CaF2 substrates with transparent (La0.07Sr0.93)SnO3

Epitaxial (La_0.07Sr_0.93)SnO₃ [LSSO] films were deposited on CaF₂ substrates by pulse laser deposition. The (1 0 0)_c orientation of LSSO films was observed only on (1 1 0)CaF₂, whereas (1 1 0)_c orientation was found on (1 1 1)CaF₂ and (1 0 0)CaF₂. (0 0 1) polar axis oriented tetragonal Pb(Zr_0.35Ti_0.65)O₃ films were grown on the fabricated (1 0 0)_cLSSO∥(1 1 0)CaF₂ by pulsed metal organic chemical vapor deposition. The (0 0 1)Pb(Zr_0.35Ti_0.65)O₃∥(1 0 0)cLSSO∥(1 1 0)CaF₂ stack structure exhibited about 70% transparency with an adsorption edge of approximately 330 nm.     

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)     

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)     

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.     

Effective electro‐optic coefficient of (1–x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 single crystals

Refractive indices and effective electro‐optic coefficient γ_c of (1–x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PZN‐xPT, x = 0.05, 0.09 and 0.12) single crystals were measured at 532 nm wavelength. Orientation and temperature dependences of the electro‐optic coefficient were investigated. Large electro‐optic coefficient (γ_c = 470 pm/V) was observed in [001]‐poled PZN‐0.09PT crystal. More importantly, γ_c of tetragonal PZN‐0.12PT is almost unchanged in a temperature range −20 ∼ 80 °C. The γ_c of PZN‐xPT single crystals are much higher than that of widely used electro‐optic crystal LiNbO₃ (γ_c = 20 pm/V). These results show that PZN‐xPT single crystals are very promising materials for electro‐optic modulators in optical communications.     

Electrochemical growth and properties of LaMn1−xCoxO3 (0 < x ≤ 1) single crystals

Single crystals of LaMn_1−xCo_xO₃ (0 < x < 1) with distorted perovskite structure have been obtained by the electrodeposition technique at anode from flux melt using Cs₂MoO₄‐MoO₃ binary system as solvent. An investigation of magnetic and electrical properties of the obtained crystals as well as its comparison with those for ceramic samples of the same composition were carried out. A much weaker interplay between magnetic and electrical properties and a smaller ∼8% magnetoresistance were found in the ternary oxide crystals slightly doped by Co on the verge of transition to ferromagnetic state in comparison to the data have been reported for LaMnO_3+δ single crystals. (© 2003 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,structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)2Sr2Ca2Cu3O10‐y crystals

Large and high‐quality single crystals of both Pb‐free and Pb‐doped high temperature superconducting compounds (Bi_1‐xPb_x)₂Sr₂Ca₂Cu₃O_10‐y (x = 0 and 0.3) were grown by means of a newly developed “Vapour‐Assisted Travelling Floating Zone” technique (VA‐TSFZ). This modified zone‐melting technique was realised in an image furnace and allowed for the first time to grow Pb‐doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm³ were successfully grown. Post‐annealing under high pressure of O₂ (up to 10 MPa at T = 500°C) was undertaken to enhance T_c and improve the homogeneity of the crystals. Structural characterisation was performed by single‐crystal X‐ray diffraction (XRD) and the structure of the 3‐layer Bi‐based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb‐free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔT_c ≤ 1 K). In optimally doped Pb‐free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�10⁵ A/cm² were measured at T = 30 K and μ₀H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40‐50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1‐5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d‐wave superconductivity in Bi‐2223. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)