Pyroelectric spectrum in Pb(Zr,Sn,Ti)O3 antiferroelectric- ferroelectric ceramics

The pyroelectric effect of phase transition induced with temperature in Nb-modified Pb(Zr,Sn,Ti)O3 antiferroelectric-ferroelectric ceramics is studied. Experimental results reveal that the phase transitions are accompanied with marked pyroelectric peaks, there exists the close relation between the type of phase transition and the shape of pyroelectric peak. Because of the variations of phase transition, various pyroelectric spectra result. The pyroelectric spectrum can display the polarization effect and some inferior phase transitions with temperature variations, such as antiferroelectric AFEA-AFEB or ferroelectric FEL-FEH transition, which are not detected by the conventional dielectric measurement.     

Structural phase transition, optical and pyroelectric properties of lead-free single crystals

0.14 at% Mn-doped 0.95(Na_1/2Bi_1/2)TiO₃-0.05BaTiO₃ (0.95NBT-0.05BT) lead-free single crystals were grown by a top-seeded solution growth method (TSSG). X-ray powder diffraction measurement showed that the as-grown single crystals exhibit rhombohedral perovskite structure with apparent distortion. With the increase of temperature, successive structural phase transitions occur in the Mn-doped 0.95NBT-0.05BT single crystals. After poling, apparent dielectric anomaly is induced accompanied by the increase of the character of diffuse phase transition and the decrease of the value of dielectric constant. The Mn-doped 0.95NBT-0.05BT single crystals exhibit complex domain structure, in which micro and macro domains coexist with statistically 4 mm symmetry. The Mn-doped 0.95NBT-0.05BT lead-free single crystals exhibit excellent piezoelectric and pyroelectric properties, which will lead to promising advance in piezoelectric and pyroelectric applications. The infrared-absorption band occurred around 630.6 cm^?1 can be assigned to the “stretching” normal vibration of [Na_1/2Bi_1/2]/Ti-O group. The three diffused Raman bands centered around 300, 560 and 800 cm^?1 can be attributed to F2g [TiO₆] bending vibration, A1g [TiO₆] stretching vibration and “soft mode” mixed by bending and stretching vibrations.     

Thermal expansion in lead zirconate titanate

The volume anomalies with temperature variations in tin-modified lead zirconate titanate ceramics are investigated. Experimental results show that the volume changes are related to the phase transitions induced with temperature. The magnitude and orientation of crystal volume changes are dependent on the particular phase transition. When antiferroelectrics is transformed to ferroelectrics or paraelectrics the volume expands. Oppositely when ferroelectrics is transformed to antiferroelectrics or paraelectrics the volume contracts. In the transition of antiferroelectric orthorhombic structure to tetragonal structure or ferroelectric low-temperature rhombohedral structure to high-temperature rhombohedral structure, there are also revealed apparent anomalies in the curves of thermal expansion. Among them, the volume strain caused by the transition between antiferroelectrics and ferroelectrics is the biggest in magnitude, and the linear expansion dL/L₀ and the expansion coefficient (dL/L ₀)/dT can reach 2.8 × 10⁻³ and 7.5 × 10⁻⁴ K⁻¹ respectively.     

铌酸钾晶体的低温热释电性

研究了铌酸钾晶体在低温时的热释电性和介电性.在相变温度范围,发现热释电响应随时间改变极性,表明晶体中两相共存.在降温和升温过程中,热释电系数分别于209K和237K出现峰值,显示此相变有约30K的热滞.这一结果与介电测量的结果相符.     

Elastic anomalies near phase transitions of lead-free （Na,Bi）TiO3 and （Ba,Zr）TiO3 ferroelectric ceramics

We have investigated the temperature dependence of elastic modulus for various ferroelectric ceramics in the temperature range of 20–90°C.The Na0.5Bi0.5TiO3(NBT)ceramics has a phase transition at 200°C,thus exhibits minimal change in elastic modulus up to 90°C,while the elastic modulus of the BaZr0.07Ti0.93O3(BZT-7)shows 12.5%change at the phase transition temperature of70°C and that of the BaZr0.15Ti0.85O3(BZT-15)ceramics shows 34.6%change at the phase transition temperature of60°C.The variations of elastic modulus will affect the temperature stability of devices made by these lead-free ferroelectric ceramics.     

Ferroelectricity of nanocrystalline BaTiO<Subscript>3</Subscript> ceramics by first principle calculation

The vibrational modes of BaTiO₃ in different crystalline phases have been investigated by means of density functional theory pseudo potential method. The evidence of tetragonal to orthorhombic and orthorhombic to rhombohedral phase transitions present for 8 nm BaTiO₃ ceramics further demonstrates that the similar successive transitions in 8 nm BaTiO₃ ceramics from rhombohedral to orthorhombic, tetragonal and cubic transitions are as those in coarse BaTiO₃ ceramics.     

A phase field study for influence of elastic energy on L1<Subscript>0</Subscript>→L1<Subscript>2</Subscript> transient ordering in Ni<Subscript>75</Subscript>Al<Subscript>17</Subscript>Zn<Subscript>8</Subscript>

The influence of the elastic energy on L1₀→L1₂ transient ordering transformation was investigated by microscopic phase field method. It is found that there are three stages experienced in atomic ordering: solute clustering+L10 short range ordering → L1₀ long range ordering → L1₂ long range ordering. Before the formation of the high ordered L1₂ phase, it has firstly taken place the transformation from matrix to L1₀ phase, and then held the L1₀→L1₂ secondary transformation. Elastic energy is proved to take little effect on the stage of short range ordering, but as the elastic energy is multiplied, it obviously shortened the course of the solute clustering, and speeded up the proceeding of the L1₀ long range ordering transition. Accordingly, the increased elastic energy also strengthens the single crystalline directionality of L1₀ phase projecting on 2D plane and makes the ordered degree of Al and Zn atoms enhanced. With the temperature elevation, Al’s and Zn’s ordered degree decreased in L10 phase.     

Phase transition , structure and shape memory effect of Ni47Ti43Hf10 alloy

A Ni₄₇Ti₄₃Hf₁₀ high temperature shape memory alloy is fabricated. The martensitic transformation temperature (TT) is obtained by differential scanning calorimetry and four-probe electrical resistivity measurements. The effect of thermal cycling is investigated and it is found that the TT tends to be stable quickly, which is of benefit to practical applications. The martensite structure is determined to be B19' monoclinic by X-ray diffraction and transmission electron microscopy. One-way and two-way (which is seldom reported before) shape memory properties are studied by tensile and bending tests. The cycling number of two-way shape memory effect is tested for more than 20000 times.     

基于差分吸收检测技术的非分散红外CO2呼吸气体传感器

采用非分散红外(non-dispersive infrared,NDIR)气体传感器实时检测呼吸气体中的CO2气体浓度,进而反映人体运动机能和代谢功能等身体状态,可以满足人类日益增强的对自身健康状况进行了解的需求.利用电调制微机电系统(micro-electro-mechanical system,MEMS)光源和双通...     

两种TGS晶体在低温下的热电和介电性

测量了TGS、ATGSP两种晶体在室温至20K温度范围内的介电常数K_(22)和热电系数p_2。这两种参数都随温度降低而单调下降,不显示相变的迹象。在此范围内的任一温度,ATGSP的热电系数p_2和优值p_2/K_(22)均较TGS的大。优值p_2/K_(22)随温度下降而减小,与自发极化的温度特性不相一致。     

Li_(0.025)Na_(0.0975)NbO_3的低温热电性及其测量

在300K至20K的温废范围内,研究了Li_(0.025)Na_(0.975)NbO_3晶体的热电性。在降温和升温过程中,热电系数分别在180K附近和260K附近显示峰值。这表示晶体中发生了低温相变而且该相变有很大的热滞(约80K)。观测了热电电荷随时间的变化。在降温和升温过程中,热电响应分别在180K附近和260K附近随时间改变极性。这一现象被认为是相变过程中两相共存的结果。     

Phenomenon of multiple field-induced phase transition in PLZST antiferroelectric ceramics

The multiple field-induced phase transition in 4 at.% La modified Pb(Zr,Sn,Ti)O 3 family with temperature from -40℃ to 45℃ in reported. Two electric field-induced transitions from a metastable antiferroelectric phase to two ferroelectric phases are observed is polarization at the applied field of 4 MV/m. The critical field of phase transition between two ferroelectric phases is not larger than 2.5 MV/m, about ten to twenty percent of that ever found in PZT based ceramics. Lattice structure is shown to be orthorhombic by X-ray diffraction. Dielectric investigation reveals a relaxor-like ferroelectric behavior. Temperature-electric field phase diagram is also presented. An appreciate kind of materials is provided to investigate multiple field-induced phase transition with PZT-based ceramics.     

Structural phase transition in nanostructured γ-Fe_2O_3

Conclusions We have found that there is an exothermal peak on the DTA curve of nanostructured γ-Fe₂O₃ sample and that this peak is not repeatable. The XRD microstructure analysis confirms for the first time that this exothermal peak corresponds to the structural phase transition from γ-Fe₂O₃ to α-Fe₂O₃. After this transition, the nanostructured Fe₂O₃ crystalline grains grow continuously with increasing temperature.     

Change of proton motive force across thylakoid membrane in soybean leaf during state transitions

Change of proton gradient across thylakoid membrane in soybean leaves was studied with millisecond delayed light emission(ms-DLE) during the coures of state transitions which were indicated by the cholrophyll fluores-cence at room temperature and 77K.When dark-adapted leaves were induced to state Ⅰ with far-red light,Fm/F0,F685/F735 and the intensity of fast phase of ms-DLE were af-fected slightly.However,during the induction to state Ⅱ with red light,both Fm/F0 and F685/F735 decreased immedi-ately and the former were quicker than the latter.In this interval,the intesity of fast phase of ms-DLE increased to a maximum and then decreased to a lower valus during the transition to stateⅡ.Nigericin,an uncoupler which elimi-nates the proton gradient across thylakoid membrane,inhib-ited the increase in the intensity of fast phase of ms-DLE during the transition to state Ⅱ.Another uncoupler,valino-mycin,which eliminates the membrane potential,did not affect the changes of the intensity of fast phase.These results suggest that the prompt increase in the intensity of fast phase of ms-DLE at the beginning of transitions to state Ⅱ is cor-related mainly with the proton gradient released from water oxidation in photosystemⅡ.     

Development of multi-functional nano-paint for energy harvesting applications

The multi-functionality of lead magnesium niobate-lead titanate/paint(PMN-PT/paint) nanocomposite films for energy harvesting via piezoelectric and pyroelectric effects is described. PMN-PT/paint films have been fabricated by a conventional paint-brushing technique to provide a low-cost, low-temperature and low–energy route to create multi-functional films. The properties investigated included dielectric constants, ε' and ε', as a function of temperature, frequency and composition. From these parameters, it is indicated that the dielectric constants and AC conductivity(σ_(AC)) increase with an increase of filler content and temperature, implying an improvement of the functionality of the films. The results revealed that σ_(AC) obeyed the relation σ_(AC) =Aω~s, and exponents, was found to decrease by increasing the temperature. The correlated barrier hopping was the dominant conduction mechanism in the nanocomposite films. The efforts were made to investigate the performance of nanocomposite films to mechanical vibrations and thermal variations. A cantilever system was designed and examined to assess its performance as energy harvesters. The highest output voltage and power for a PMN-PT/paint based harvester with a broad frequency response operating in the-31-piezoelectric mode were 65 mV and 1 nW, respectively.Voltage and power were shown to be enhanced by application of thermal variations. Thus, films could be utilized for combined energy harvesting via piezoelectric and pyroelectric characteristics.     

TiO_2含量对低镁含锰渣的流动性和热力学性质的影响

为探究钛矿护炉和锰矿洗炉条件下TiO_2对炉渣流动性和热力学性质的影响机理,本文通过黏度实验和FactSage热力学软件计算,分析了不同TiO_2含量低镁含锰渣的黏度和熔化温度、热焓及活度等热力学性质变化。结果表明,随着TiO_2含量的增加,炉渣黏度、熔化性温度和完全熔化温度降低,炉渣的流动性和热稳定性改善。炉渣热焓和液相中的TiO_2活度随TiO_2含量的增加而增大,而热焓的增大将增加高炉的热量消耗和燃料比。在冷却结晶过程中,TiO_2含量的增加有利于增大钙长石、钙钛矿和橄榄石等物相的析出量,而黄长石和硅灰石的析出量则随TiO_2含量的增加而降低。     

A doubling of the post-perovskite phase boundary and structure of the Earth's lowermost mantle

The thermal structure of the Earth's lowermost mantle--the D' layer spanning depths of approximately 2,600-2,900 kilometres--is key to understanding the dynamical state and history of our planet. Earth's temperature profile (the geotherm) is mostly constrained by phase transitions, such as freezing at the inner-core boundary or changes in crystal structure within the solid mantle, that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory. A recently discovered phase transition at pressures of the D' layer is ideally situated to reveal the thermal structure of the lowermost mantle, where no phase transitions were previously known to exist. Here we show that a pair of seismic discontinuities observed in some regions of D' can be explained by the same phase transition as the result of a double-crossing of the phase boundary by the geotherm at two different depths. This simple model can also explain why a seismic discontinuity is not observed in some other regions, and provides new constraints for the magnitude of temperature variations within D'.     

SrCl2晶体高压结构转变的第一性原理计算

利用基于密度泛函的第一性原理, 计算SrCl2压致结构转变的压力. 结果表明： SrCl₂在2.1 GPa处发生第一个压致结构转变, 由萤石结构（空间群Fm3m）转变为正交结构（空间群Pnma）; 在65.7 GPa处发生第二个压致结构转变, 由正交结构转变为六角结构（空间群P6₃/mmc）; 两个压致结构转变均发生体积突变, 分别为4.7%和0.2%, 均属于一级相变.     

锆钛酸铅多晶材料的FR（LT）—FR（HT）相变及其热释电性质

本文研究了用共沉淀技术制备的PZT四种菱方相组分的均匀单相多晶体的介电特性和热释电特性。实验发现。菱方—菱方相变点的极化强度的异常变化是材料组成的函数。从组成PZT90/10和PZT94/6多晶体样品上可观察到介电系数、极化强度和热释电系数随温度发生的异常变化。但对于菱方组分PZT60/40和70/30却只能观察到热释电性质的异常变化。该二组分多晶体的相转变温度范围十分宽。文中引进铁电唯象理论描述了F_(R(LT))—F_(R(HT))相变行为。     

Effects of temperature on hydrostatic pressure-induced FE-AFE phase transition in PbLa(Zr, Sn, Ti)O3 ceramics

Hydrostatic pressure-induced ferroelectricantiferroelectric (FE-AFE) phase transition and the pressure dependence of dielectric properties in La-doped Pb(Zr,Sn, Ti)O₃ ceramics were researched; the effects of temperature on hydrostatic pressure-induced FE-AFE phase transition and dielectric properties of the samples were studied. It was found that the temperature made the FE-AFE phase transition pressure decrease, and there existed the behavior of dielectric frequency dispersion and phase transition diffusion in the dielectric-pressure spectrum. These phenomena were very useful to enrich and develop the knowledge on the diffused phase transition behavior of polycomponent relaxor ferroelectric.