Structural and dielectric properties of Pb(Li1/4Dy1/4W1/2)O3

The polycrystalline samples of Pb(Li_1/4Dy_1/4W_1/2)O₃ have been synthesized by high-temperature solid-state reaction techniques. Room temperature X-ray diffraction (XRD) studies of the compound provided preliminary structural data, and hence formation of a single phase desired material was confirmed. Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (100 Hz to 10 kHz) at room temperature (298 K) and also as a function of temperature (liquid nitrogen to 403 K) at 10 kHz suggest that the compound undergoes a ferroelectric phase transition of diffuse type.     

Synthesis and dielectric properties of Ba3NaRNb10O30 [R = La and Sm]

Polycrystalline samples of Ba₃NaRNb₁₀O₃₀ (R = La and Sm) have been prepared by high temperature solid-state reaction method. The X-ray powder diffraction technique has been used to test the formation of the compounds. Lattice parameters, space groups and basic structures of the compounds have been obtained from X-ray data. The dielectric constant has been measured as a function of frequency (100 Hz–10 kHz) and temperature (−180 to 200°C) to understand transition mechanism in these ferroelectric compounds.     

X-ray and dielectric studies of Sm2(MoO4)3

The polycrystalline samples of Sm₂(MoO₄)₃ have been prepared by heating appropriate quantities of oxides. The X-ray powder diffraction technique has been used to provide information about lattice parameter, space group and basic structure. The dielectric constant has been measured as a function of frequency (560 Hz-13 MHz) and temperature (30–220°C) to know the ferroelectric transition temperature.     

EPR and dielectric properties of Pb5Ge3O11 crystals with off-center Cu2+ ions

The electron paramagnetic resonance (EPR) and dielectric properties of Pb₅Ge₃O₁₁ crystals activated by copper ion are investigated. It is shown that Cu²⁺ ions replace Pb²⁺ in trigonal symmetry positions and occupy three off-center positions displaced from a crystal lattice site in a plane perpendicular to the polar axis C. The temperature variation of EPR spectra and dielectric properties indicates the presence of thermally activated jumps of Cu²⁺ ions between off-center positions. The EPR and dielectric data are used to determine the activation energy W=0.24 eV and the eigenfrequency τ ₀ ^?1 ～ 10¹² Hz of local dynamics of Cu²⁺ ions.     

(PbBa)(Zr,Sn,Ti)O_3反铁电/弛豫型铁电相界陶瓷的相变与介电、热释电性质

通过对(Pb087Ba01La002)(Zr06TixSn04-x)O3(004≤x≤020)固溶体的介电和偏压热释电性质的研究发现,当Ti含量004≤x≤007时,材料是反铁电四方相,而当009≤x≤020时,材料向弛豫型铁电体转化.在温度Ti含量相图中,x=009附近形成了反铁电铁电顺电三相共存点(Ttr).该点的相变温度最底;对于004≤x≤007的反铁电四方相,低温下呈现介电弛豫特征,并可被外电场诱导为亚稳铁电态,温度升高时,亚稳铁电→反铁电相变,反铁电→顺电相变引起两个热释电流峰,偏置电场下峰位和峰强均发生移动,在温度电场相图中也形成了铁电反铁电顺电三相点.从复杂化合物纳米相分离的观点和晶格动力学出发,讨论了相变与电学性能随Ti含量(x)和外电场(E)变化的物理机理. 关键词： 反铁电/弛豫型铁电相界 介电性能 偏压热释电性质 铁电-反铁电-顺电三相点     

Dielectric properties of Pb(Mg1/4Zn1/4Nb1/2)O11/4

Polycrystalline samples of Pb(Mg_1/4Zn_1/4Nb_1/2)O_11/4 have been synthesized by high temperature columbite precursor solid state reaction technique. Using X-ray diffraction (XRD) technique, compound formation in single phase cubic structure was observed and XRD analysis provided preliminary structural data. Detailed studies of dielectric properties of the compound reveal that this compound has high dielectric constant and diffuse phase transition in a wide range of temperatures around the Curie temperature. The charge deficiency of the compound presumably gets compensated in the high temperature columbite precursor process of sample preparation which is supported by single phasic form of the material.     

Effect of Misfit Strain on Pyroelectric Properties of (111) Oriented Pb(Zr1-xTix)O3 Thin Films

Based on the Landau-Dovenshire theory, the thermodynamic potential of (111) oriented films is constructed to investigate the pyroelectric properties of Pb(Zr_1-xTi_x)O₃ thin films. Due to the presence of nonlinear coupling terms resulted from the (111) epitaxy with substrates, the effects of misfit strain and electric field on the phase transitions at room temperature are more complex than that of (001) and (110) oriented films. Pb(Zr_0.5Ti_0.5)O₃ thin films with the Ti composition around the morphotropic phase boundary (MPB) have the giant dielectric and pyroelectric properties. Moreover, Pb(Zr_1-xTi_x)O₃ thin films grown on the tensile substrates which induce the triclinic γ phase have the larger dielectric and pyroelectric properties than that on the compressive substrates. Therefore, the physical properties of (111) oriented Pb(Zr_1-xTi_x)O₃ thin films can be adjusted by choosing the suitable substrates.     

Second-order ferroic properties of a Pb5Ge3O11 uniaxial ferroelectric

The ferrobielastic properties (ferroic properties of the second order) earlier theoretically predicted for lead germanate uniaxial ferroelectric crystals are justified experimentally. It is demonstrated that single-domain samples are formed upon cooling to temperatures below the Curie point under uniaxial mechanical stresses corresponding to a combination of mechanical stresses σ₁₁σ₁₃ or σ₂₂σ₂₃. The macroscopic mechanism of this phenomenon is considered.     

Effect of Sb doping on phase transition and relaxor behaviour of (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 ceramics

The effect of antimony dopant on phase transition, dielectric response and relaxor behaviour of (Pb_0.75Ba_0.25)(Zr_0.70Ti_0.30)O₃ ceramics was studied. Ceramic samples, with various Sb concentration from the range 1 to 4 at.%, were prepared by a conventional mixed oxide method. The crystal structure of the investigated ceramics was determined by an X-ray diffraction at room temperature that allowed to determine the unit cell parameters. Dielectric relaxation typical for ferroelectric relaxors was observed in the vicinity of diffuse ferroelectric–paraelectric phase transition. All parameters describing the relaxor behaviour determined from the Vogel–Fulcher relationship depend on the concentration of Sb dopant. The strong influence of antimony on grain structure and on remanent polarisation was confirmed as well.     

Structural,spectroscopic and dielectric properties of KVO3

Polycrystalline samples of KVO₃, a member of the pyroxene structural family have been synthesised with high-temperature solid-state reaction technique. Preliminary structural and spectroscopic and detailed dielectric properties have been studied in different conditions. No dielectric anomaly or hysteresis loop has been observed in a wide temperature range (30°C to 450°C). Basic structural and spectroscopic (IR and Raman) studies suggest that at room temperature, KVO₃ is centrosymmetric as reported earlier. This and other observations do not support the recent report of ferroelectric phase transition in the compound.     

Structural and dielectric properties of phosphorous-doped PLZT ceramics

In the present work we have reported the unique effects of P₂O₅-doped PLZT ceramics with composition (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ +x wt% of P₂O₅ (wherex = 1, 3 and 5) prepared chemically by co-precipitation method. X-ray diffraction studies suggest that the prepared compound was very fine (10–25 nm), homogeneous and of rhombohedral symmetry. The apparent density of samples decreased with the P⁵⁺ additions. Studies of dielectric constant and dielectric loss as a function of frequency (10–1000 kHz) and temperature suggest that the compound undergoes diffuse type of phase transition without any sign of relaxor behaviour. With increasingx, dielectric constant was found to decrease appreciably, whereas Curie temperature (T_C) was found to increase     

Uniaxial pressure influence on dielectric properties of Pb(Zr0.99Ti0.01)O3 single crystals

The effect of uniaxial pressure (0–1000 bars) applied parallel to AC electric field on dielectric properties of Pb(Zr_0.99Ti_0.01)O₃ single crystals has been investigated. It was found that uniaxial pressure significantly influences these properties. With increasing pressure: (i) peak ?(T) decreases, becomes diffuse and shifts to higher temperature, (ii) the thermal hysteresis is reduced, (iii) the hump in ?(T) profile connected with antiferroelectric–intermediate phase transition vanishes, and (iv) the local anomaly in ?(T) profile connected with polar microregions existence above T_m is protruded and slightly shifts towards higher temperature. It was concluded, that applied uniaxial pressure or increasing Ti-ions content in lead zirconate titanate system induces similar effects. The results were discussed in terms of domain switching under pressure.     

Dielectric and infrared properties of SrTiO3 single crystal doped by 3d （V,Mn, Fe,Ni） and 4f （Nd,Sm, Er） ions

In this study, the effects of doping by 3d （V, Mn, Fe, Ni） and 4f （Nd, Sm, Er） ions on dielectric and infrared properties of SrTiO3 （STO） single crystals are investigated. It is well known that doping of the SrTiO3 can change the dielectric properties of the STO from an insulator to an n-type semiconductor, and even to a metallic conductor. Dielectric and infrared （IR） properties of the undoped STO and doped STO single crystals are analyzed using dielectric spectroscopy （80 kHz-5 MHz）, transmission （200 cm^-1-4000 cm^-1）, and reflection spectroscopy （50 cm^-1-2000 cm^-1）. It is found that doping by the 3d ions reduces the value of dielectric permittivity, but the trend of temperature dependence of the dielectric permittivity remains almost unchanged. On the other hand, dielectric spectroscopy measurements for samples doped by 4f ions show the anomalous behaviors of the dielectric permittivity at temperatures around the temperature of the structural phase transition. There are two fractures of temperature dependences of inverse dielectric permittivity εr^-1 （T）. Transmittance spectroscopy measurements show that there are differences in the shape of the spectrum in the mid-IR region between the undoped STO and the one doped by 4f ions. The differences in the reflectance spectrum between the STO：Nd and STO are analyzed in detail.     

锆钛酸钡陶瓷的电场诱导相变特性研究

Ba（Zr0.2Ti0.8）O3（BZT）陶瓷，其铁电相变温度接近室温。对BZT陶瓷的电场诱导相变进行了研究，结果表明介电常数随着电场的增加而减小，预示着电场诱导相变行为。电场强度影响陶瓷的介电常数峰值的位置，并且在广泛温度范围内影响介电常数的大小。介电常数峰值位置随电场的变化量△Tm与电场满足如下关系：△Tm～E^2/3，说明BZT发生了类似的二级相变行为。     

High pressure raman scattering in Pb5Ge3O11

The pressure dependence of various phonon modes has been investigated through the ferro-paraelectric phase transition. Most mode frequencies harden before levelling off above the phase transition. Mode Grüneisen parameters are estimated from the pressure dependence of phonon frequencies.     

Observation of the ferroelectric phase transition in Pb5Ge3O11 by the chemical potential changes

We observed the transition from the ferroelectric (FE) to paraelectric (PE) phase in the semiconducting, ferroelectric Pb₅Ge₃O₁₁ single crystal with the use of the contact electrode method. To this purpose a thin, metallic layer was placed onto the Pb₅Ge₃O₁₁ crystal surface, forming the contact electrode. At opposite ends of the contact electrode, silver wires were glued and a voltage was applied to the contact electrode in such a way that the electric current could flow only through the attached electrode. The electric resistance R(T) of the electrode was measured as a function of temperature. Two series of measurements were performed. In one of them the ferroelectric c-axis of the investigated crystal was perpendicular to the contact electrode. In the second one the c-axis was parallel to the attached electrode. We used gold as the contact electrode material. The anomaly in the R(T) in a form of a kink at T _kink?=?452?K was found for both c-axis orientations. The measured value of T _kink, appearing in the temperature dependence of contact electrode resistance, corresponds exactly to the phase transition temperature T _C from the FE to PE phase of the investigated Pb₅Ge₃O₁₁ material. This result demonstrates that the contact electrode method, primarily proposed exclusively to find critical temperatures of metallic samples, also works well in the case of ferroelectric and semiconducting materials like Pb₅Ge₃O₁₁. We ascribe the effect of the resistance kink in the temperature dependence of the contact electrode R(T) to thermal excitations of the electrons with different rates below and above T _C due to different electronic activation energies in the FE and PE phases of the investigated Pb₅Ge₃O₁₁ crystal. It, however, means that the phase transition in the electronic subsystem of the Pb₅Ge₃O₁₁ transfers into the electron gas of the contact electrode via the chemical potential relation µ _sample?=?µ _electrode due to the contact between the sample and the electrode. The magnitude of the kink, observed in the R(T) dependence, was higher on heating than on cooling. The additional measurement of the thermally stimulated current (TSC) was carried out on the non-polarised Pb₅Ge₃O₁₁ sample. In this series of measurements, the sample was covered with gold layers sputtered on the two opposite surfaces of the crystal. The TSC anomaly occurred, related to the residual pyroelectric effect, several degrees below the Curie temperature, T _C, and does not disturb the detection of the critical point with the use of the contact electrode method.     

Structural phase transition on Si(001) and Ge(001) surfaces

Among a variety of solid surfaces, Si(001) and Ge(001) have been most extensively studied. Although they seem to be rather simple systems, there have been many conflicting arguments about the atomic structure on these surfaces. We first present experimental evidence indicating that the buckled dimer is the basic building block and that the structural phase transition between the low-temperature c(4x2) structure and the high-temperature (2x1) structure is of the order-disorder type. We then review recent theoretical work on this phase transition. The real system is mapped onto a model Ising-spin system and the interaction parameters are derived from total-energy calculations for different arrangements of buckled dimers. The calculated critical temperature agrees reasonably well with the experimental one. It is pointed out that the nature of the phase transition is crucially affected by a small amount of defects on the real surfaces.     

Linear and nonlinear dielectric properties of nanocomposites based on the organic ferroelectric of diisopropylammonium bromide

ABSTRACT

The present work aims at investigating linear and nonlinear dielectric properties of nanocomposites based on diisopropylammonium bromide (C₆H₁₆NBr, DIPAB) embedded into Al₂O₃ films having honeycomb structure with pores of 100?nm in diameter, and into opal matrices with three-dimensional structure containing pores of 100 and 60?nm. The obtained results indicated the shift of Curie point toward lower temperatures for DIPAB in porous aluminum oxide and the appearance of two phase transitions, detected upon heating and cooling for DIPAB in opal matrices. In addition, a ferroelectric phase was found to form between these two phase transitions without significant change of Curie temperature.     

La调节Pb(Zr,Sn,Ti)O_3反铁电陶瓷的相变与电学性质

利用X射线衍射、弱场介电温度谱、强场极化强度研究了不同La含量(Pb1-xLa2x3)(Zr06Sn03Ti01)O3(000≤x≤012)(PLZSnT)陶瓷的相变与电学特性.实验发现,随La含量增大,室温下材料由铁电三方相(x=000)转变为反铁电四方相(003≤x≤009)和立方相(x=012).介电测试表明,La含量增大,反铁电→顺电相变温度降低,峰值介电常量减小.在x=006的PLZSnT三元相图中,反铁电四方相区扩大到Ti含量约为18at%,该系统反铁电陶瓷具有“窄、斜”型双电滞回线和“三电滞回线”;在高Zr、高Sn区,反铁电→顺电相变呈现弥散相变和介电频率色散特征,即反铁电极化弛豫现象.从ABO3钙钛矿结构的容忍因子(t)和反铁电相的结构特征出发,讨论了La对Pb(Zr,Sn,Ti)O3相变与电学性质的影响机理 关键词： 场诱相变 弛豫型反铁电体 介电性能 La调节Pb(Zr Sn Ti)O3