Dielectric properties of solid solutions PbMg1/3Nb2/3O3-SrTiO3

Ceramic samples of the solid solutions PbMg_1/3Nb_2/3O₃-SrTiO₃ are synthesized. The dielectric properties are studied and a phase diagram is constructed. The results obtained are discussed in terms of ideas concerning relaxor ferroelectrics for solid solutions on the PMN side and from the standpoint of potential ferroelectrics on the SrTiO₃ side. The introduction of SrTiO₃ into PMN gradually degrades relaxor properties, and the introduction of PMN into SrTiO₃ does not result in initiation of the ferroelectric phase transition, possibly because of the appearance of random fields in the lattice. The possibility of practical applications of the synthesized system is also discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 1091–1095 (June 1999)     

Study of the ion mobility in a Li0.03Na0.97Ta0.4Nb0.6O3 solid solution by raman spectra

We have studied ion mobility in a Li_0.03Na_0.97Ta_0.4Nb_0.6O₃ solid solution by its Raman spectra. It has been revealed that, as the temperature of the solution is increased to approach the point of the phase transition to a state with a high conductivity with respect to lithium, the lines with frequencies at 77, 118, and 142 cm^?1, which refer, respectively, to librations of oxygen octahedra Nb(Ta)O6 as a whole and vibrations of Li and Na ions in octahedra, considerably broaden, decrease in intensity, and smear into the wing of the Rayleigh line. Remaining lines are preserved in the spectrum. We have observed that the width of the line with a frequency of 118 cm^?1 depends exponentially on temperature, while the width of the line with a frequency of 142 cm^?1 changes linearly with it, which makes it possible to attribute to the line with the frequency of 118 cm^?1 to vibrations of Li⁺ cations, whereas the line with the frequency of 142 cm^?1 should be attributed to vibrations of Na⁺ cations in AO₁₂ cuboctahedra. The average lifetime of Li⁺ ions in equilibrium positions and the jump barrier have been estimated to be ～8 × 10^?12 s and ～20 kJ/mol, respectively. This agrees well with the data in the literature on measurements of electric conductivity.     

Raman Spectra Study on LiTa0.9Nb0.1O3 Single Crystal

In this letter, Raman spectra of LiTa_0.9Nb_0.1O₃ single crystal in both of its ferroelectric phase and paraelectric phase are presented for the first time. Comparing with LiTaO₃ crystal, we find that the distribution and Raman shifts of normal vibrational mades are similar, but the line-shape and relative intensities of these modes have changed.     

Dielectric response of K(Ta,Nb)O3 thin films

The dielectric response of K(Nb,Ta)O₃ films grown on (001) MgAl₂O₄ (100) by pulsed laser deposition from a mosaic target of KTa_0.63Nb_0.37O₃ and KNO₃ has been examined. In particular, the effects of growth temperature (650–800 °C), growth pressure (1–100 mTorr O₂), and annealing conditions on the tunability, dielectric constant, and dielectric losses in interdigitated capacitor device structures fabricated with these films are described. Annealing treatments lead to a reduction in the loss tangents for most of the films considered. Figure of merit calculations indicate that the best dielectric response (tunability=37%, tan =0.022) is achieved for films grown at 750 °C in an oxygen pressure of 100 mTorr and then annealing at 1000 °C for 2 h in air.     

Enhanced piezoelectric properties and lowered sintering temperature of Ba(Zr0.07Ti0.93)O3 by B2O3 addition

The effects of B₂O₃ doping on densification, ferroelectric, and piezoelectric properties of Ba(Zr_0.07Ti_0.93)O₃(BZT) ceramics were investigated. The addition of B₂O₃ to the ceramics lowered the sintering temperature by ∼200 °C as well as changed their microstructures. Higher B₂O₃ concentration caused a decrease in remanent polarization and coercive field, while the piezoelectric coefficient d₃₃ remained at a high value of 291 pC/N for the ceramic sample with 2 wt.% B₂O₃. The relationship between piezoelectric properties and ferroelectric constant was examined.     

Synthesis and electrochemical properties of Li8 − x Zr1 − x Nb x O6 solid solutions

New lithium-conducting solid solutions based on lithium orthozirconate have been synthesized by mutual doping of the related structures Li₈ZrO₆ and Li₇NbO₆. The main factor determining the increase in the electrical conductivity of the Li_{8 ? x} Zr_{1 ? x} Nb _x O₆ solid solutions is the formation of lithium vacancies in the tetrahedral and octahedral layers. The practical stability of the Li_{8 ? x} Zr_{1 ? x} Nb _x O₆ ceramics to metallic lithium has been studied.     

弛豫铁电单晶0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3的电光性能研究

以波长为632.8 nm的He-Ne激光作为光源,研究了三方相弛豫铁电单晶0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3在室温下的折射率和线性电光性质.通过测量晶体的布儒斯特角,确定了单晶的两个主轴折射率:no=2.466,ne=2.488.利用改进的马赫-泽德尔干涉法测量了单晶的线性电光系数:r33=71 pm/V,r13=4 pm/V.计算得到有效电光系数rc=67 pm/V及半波电压Vπ=610 V.单晶优异的电光性能使其在激光调制与偏转领域有着巨大的应用潜力.     

Galvanomagnetic properties of La0.7Sr0.3Mn0.9Cu0.1O3

La_0.7Sr_0.3Mn_0.9Cu_0.1O₃ ceramic samples have been obtained by the conventional method of the solid-phase reaction, and their resistivity ρ has been investigated in a temperature range from 50 to 300 K in magnetic fields B = 0–20 T. Dependences are typical of perovskite manganites with a maximum at T _max = 140–150 K and an increase in ρ near T _max with increasing external magnetic field B. It has been established that the behavior of resistivity is caused by the variable range hopping conduction mechanism ρ(T) = ρ₀(T)exp[(T ₀/T)^1/4], where ρ₀(T) ～ T ^25/4. The Mott variable range hopping conduction has been observed below the Curie temperature for La_0.7Sr_0.3Mn_0.9Cu_0.1O₃ samples (T _C ～ 300 K) in a temperature range from 300 to 200 K. The influence of Cu doping on the properties of La_0.7Sr_0.3MnO₃ samples is apparently caused by an additional distortion introduced into the crystal lattice of the material and by a weakening of the double-exchange mechanism.     

Dielectric relaxation and ac conduction in multiferroic Bi0.8Gd0.1Pb0.1Fe0.9Ti0.1O3 ceramics: impedance spectroscopy analysis

ABSTRACT

The solid solutions of Bi_0.8Gd_0.1Pb_0.1Fe_0.9Ti_0.1O₃ have been prepared by the solid-state reaction method. The preliminary structural studies were carried out by X-ray diffraction technique showing the formation of polycrystalline sample with ABO₃ type of perovskite structure with hexagonal symmetry for the Bi_0.8Gd_0.1Pb_0.1Fe_0.9Ti_0.1O₃ ceramic system at room temperature. Dielectric properties and impedance study of this ceramic have been characterized in the temperature range room temperature to 375 °C and frequency range 100 Hz–1 MHz. The maximum ferroelectric transition temperature (T_c) of this system was in the range 200 °C–260 °C with the dielectric constant of peak to be ～30,170 at 1 kHz. The complex impedance plot exhibited one impedance semicircle observed at low temperature, whereas two semicircles above 80 °C and the centres of the semicircles lie below the real axis, which indicates that the material is non-Debye type. Single semicircle is explained by the grain effect of the bulk and double semicircle is due to the bulk and grain boundary effect. The bulk resistance and grain boundary resistance of the materials decrease with the increasing temperature, showing negative temperature and a typical semiconducting property, i.e. negative temperature coefficient of resistance behaviour.     

Optical spectra of (CdF2)0.9(InF3)0.1 semiconductor solid solutions

The differences in the optical spectra of CdF₂:In semiconductors with bistable DX centers (concentrated (CdF₂)_0.9(InF₃)_0.1 solid solutions) and “standard” samples with a lower impurity concentration used to record holograms are discussed. In contrast to the standard samples, in which complete decay of two-electron DX states and transfer of electrons to shallow donor levels may occur at low temperatures, long-term irradiation of a (CdF₂)_0.9(InF₃)_0.1 solid solution by UV or visible light leads to decay of no more than 20% deep centers. The experimental data and estimates of the statistical distribution of electrons over energy levels in this crystal give the total electron concentration, neutral donor concentration, and concentration of deep two-electron centers to be ～5 × 10¹⁸ cm^?3, ～9 × 10¹⁷ cm^?3, and more than 1 × 10²⁰ cm^?3, respectively. These estimates show that the majority of impurity ions are located in clusters and can form only deep two-electron states in CdF₂ crystals with a high indium content. In this case, In³⁺ ions in a limited concentration (In³⁺ (～9 × 10¹⁷ cm^?3) are statistically distributed in the “unperturbed” CdF₂ lattice and, as in low-concentrated samples, form DX centers, which possess both shallow hydrogen-like and deep two-electron states.     

Evaluation of a cobalt-free Ba0.5Sr0.5Fe0.9Nb0.1O3?δ cathode material for intermediate-temperature solid oxide fuel cells

A cobalt-free Ba_0.5Sr_0.5Fe_0.9Nb_0.1O_3??? (BSFNb) perovskite-type oxide was investigated as the cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte. XRD results showed that BSFNb cathode was chemically compatible with the electrolyte SDC up to 1,000?°C. The maximum output of anode-supported thin-film SOFC reached 503?mW?cm^?2 at 650?°C when employing humidified H₂ as fuel and static air as oxidizer. The electrode polarization resistance was low as 0.078????cm² at 650?°C, and the activation energy of the electrode polarization resistance was 129.72?kJ?mol^?1. The experimental results indicated that the cobalt-free BSFNb was a promising cathode candidate for IT-SOFCs.     

Preparation and dielectric properties of BaZr0.1Ti0.9O3 ceramics with different grain sizes

BaZr_0.1Ti_0.9O₃ ceramics with grain sizes of 0.75 and 2.60?µm have been prepared via solid-state reaction. Optimum parameters for calcination and sintering have been found in order to obtain pure perovskite phase, high density ceramics and homogeneous microstructures. The dielectric data show a diffuse phase transition with a mixed ferroelectric-relaxor character at a maximum at 87–92°C, with a small thermal hysteresis of 2–3°C. A tendency towards a more diffuse character of the ferro–para phase transition towards the full relaxor behaviour is observed as small in the ceramic grain size. Better dielectric properties in the coarse ceramics with higher permittivity up to 14,000 at the transition temperature by comparison with 5000 for the fine one, are observed as a consequence of higher tetragonal distortion and higher density. The differences in the dielectric spectra found for the two grain sizes were interpreted as a consequence of the higher degree of inhomogeneity in the fine ceramics and to different grain boundary properties induced by the different sintering temperatures.     

Microstructural and electrical properties of Y0.07Sr0.93-x TiO3-δ perovskite ceramics

In order to find a relationship between electrical and microstructural properties, yttrium-doped strontium titanate (7 mol%) with various values of strontium nonstoichiometry was investigated and shown in this work. It has been observed that yttrium doping can affect the electrical properties of SrTiO₃ to a great extent. Moreover, the microstructural and electrical properties can be influenced by strontium nonstoichiometry. The defect chemistry explaining obtained results was also suggested and discussed.     

The effect of some transition metal oxides on the physical properties of K0.5Na0.5Nb0.95Ta0.05O3 ceramics

Abstract

Both K_0.5Na_0.5Nb_0.95Ta_0.05O₃ (KNNTO) and (K_0.5Na_0.5Nb_0.95Ta_0.05O₃)_0.99-M_0.01, M = Co₃O₄ and Mn₂O₃ (M/KNNTO) Ferromagnetic behaviour was observed for some M/KNNTO compounds. The hardness and compressive strength of all investigated samples are given. Comparisons with similar materials are discussed. Ceramics were synthesised using a solid-state reaction method. X-ray diffraction patterns of all samples revealed that the crystal structure is orthorhombic. Field-emission scanning electron microscopy was performed. Polarisation hysteresis curves indicated a disruption of ferroelectric order with the addition of M into KNNTO ceramics. The dielectric properties of the investigated ceramics have been studied as a function of frequency and temperature.     

Preparation and ferroelectric properties of pyrochlore-free Pb(Ni1/3Nb2/3)O3-based solid solutions

Polycrystalline ceramics of the perovskite solid solution 0.5Pb(Ni_1/3Nb_2/3)O₃-(0.5-x)-Pb(Zn_1/3Nb_2/3)O₃–xPb(Zr_1/2Ti_1/2)O₃; x=0.0–0.5 (PNN–PZN–PZT) were synthesized by a modified columbite method. Highly dense ceramics lacking parasitic pyrochlore phases were prepared at a calcination temperature of 950 °C by using a double-crucible configuration, excess PbO (2 mol %), and a fast heating/cooling rate (20 °C/min). The ceramics were characterized by a variety of techniques including X-ray diffraction, ferroelectric hysteresis loop measurements, field-induced longitudinal strain measurements, and electron microscopy. It was observed that the remanent polarization exhibited a significant increase with increasing x. In addition, the squareness of the hysteresis loop increased quasi-linearly as the molar fraction of PZT increased. The maximum spontaneous polarization and remanent polarization for the x=0.5 composition were 31.9 μC/cm² and 25.2 μC/cm², respectively. Moreover, the data were analyzed to show the evolution of the micro-domain state as a function of the molar fraction of PZT. PACS 77.22.-d; 77.80.Bh; 77.84.Dy; 61.10.Nz; 77.80.Dj     

Dielectric and photoelectric properties of Pb(Mg1/3Ta2/3O3 crystals

The temperature dependence of the dielectric constant ɛ and the spectral dependence of the photoconductivity of Pb(Mg_1/3Ta_2/3)O₃ crystals are investigated. The width of the band gap (3.4 eV) is determined. It is found that above the temperature of the maximum of the dielectric constant, its reciprocal 1/ɛ varies with temperature first quadratically and then according to a linear law, as is characteristic of ferroelectrics with a smeared phase transition. The smearing parameter of the transition estimated from the experimental data is close to the value calculated assuming the absence of long-range order in the arrangement of the Mg and Ta ions. Fiz. Tverd. Tela (St. Petersburg) 40, 109–110 (January 1998)     

Large quadratic electro-optic effect in K0.99Li0.01Ta0.60Nb0.40O3 single crystal

Single crystal paraelectric K_0.99Li_0.01Ta_0.60Nb_0.40O₃ is grown with a room-temperature Curie temperature (T_c). The parameters of the Sellmeier dispersion equation were determined. A large quadratic electro-optic (QEO) effect was observed. The QEO coefficient R₁₁ reaches as high as 2.48 × 10^?15 m² V^?2 around T_c. The induced refractive index change under an electric field of 500 V/mm is 40 times bigger than that of commonly used LiNbO₃. The large QEO coefficient makes single crystal K_0.99Li_0.01Ta_0.60Nb_0.40O₃ a promising candidate in optical devices.     

PbZr0.4Ti0.6O3 and Ba0.9Sr0.1TiO3 reflectors derived from chemical solutions containing polymers

Ba(0.9)Sr(0.1)TiO(3) (BST)-based and PbZr(0.4)Ti(0.6)O(3)-based quasi-periodic multilayers consisting of dense and porous ferroelectric layers have been fabricated by solgel technique using chemical solutions containing polyethylene glycol (PEG) or polyvinylpyrrolidone k30 (PVP). All multilayers exhibit good performance as dielectric mirrors. For each multilayer, the maximum peak reflectivity is over 90% and the photonic stopband width is no less than 30 nm at room temperature. The reflection-band position can be easily tuned by varying the thickness of the bilayer. With the same processing conditions and number of periods, the Bragg reflection performance is almost the same for quasi-periodic PZT multilayers derived from two precursors containing different polymers. The BST multilayers deposited by using a PVP-containing precursor are superior in optical properties, including peak reflectivities and stop-band width, to those deposited by using the PEG-containing solution.