Improved multiferroic properties of La-doped 0.6BiFeO3—0.4SrTiO3 solid solution ceramics

The 0.6（Bi1-xLax）FeO 3-0.4SrTiO 3（x = 0,0.1） multiferroic ceramics are prepared by a modified Pechini method to study the effect of substitution of SrTiO3 and La in BiFeO3.The X-ray diffraction patterns confirm the single phase characteristics of all the compositions each with a rhombohedral structure.The magnetic properties of the ceramics are significantly improved by a solid solution with SrTiO3 and substitution of La.The values of the dielectric constant ε r and loss tangent tan δ of all the samples decrease with increasing frequency and become constant at room temperature.The La-doped 0.6BiFeO3-0.4SrTiO3 ceramics exhibit improved dielectric and ferroelectric properties,with higher dielectric constant enhanced remnant polarization（Pr） and lower leakage current at room temperature.Compared with a anti-ferromagnetic BiFeO3 compound,the 0.6（Bi0.9La0.1）FeO3-0.4SrTiO3 sample shows the optimal ferromagnetism with remnant magnetization M r ～ 0.135 emμ/g and ferroelectricity with Pr ～ 5.94 μC/cm 2 at room temperature.     

Dielectric properties of perovskite ceramics of (1–x)BiFeO3 ? x(KBi)1/2TiO3 (0.40 < x < 0.85) solid solutions from impedance spectroscopy data

The dielectric properties of the ceramics of (1 − x)BiFeO₃ − x(KBi)_1/2TiO₃ (0.40 < x < 0.85) solid solutions with an orthorhombic structure have been studied using impedance spectroscopy in the frequency range 25–10⁶ Hz at different temperatures. It has been shown that these solid solutions undergo a diffuse ferroelectric phase transition. The Curie temperature is found to be in the range 620–640 K. The activation energies of dielectric polarization relaxation (δE _M ) and dc charge carriers (ΔE _dc) are determined. It has been established that, in the vicinity of 460 K, ΔE _dc increases jumpwise as the temperature increases.     

Effect of Sc substitution on the structure,electrical, and magnetic properties of multiferroic BiFeO3 thin films grown by a sol–gel process

Multiferroic BiFeO₃ (BFO), Bi_1−xSc_xFeO₃ (BSF), and BiFe_1−xSc_xO₃ (BFS) (x=0.3 mol%) thin films are prepared on Pt/Ti/SiO₂/Si substrates using a sol–gel technique. The effect of Sc substitution along with the annealing ambient (N₂ and O₂) on the structure, electrical, and magnetic properties of the films are reported. X-ray diffraction (XRD) analysis reveals that the films can be prepared with the single-phase perovskite structure by annealing at 700 °C for 10 min either in O₂ or N₂ ambient. The unit cell volume increases on the substitution of Sc, which are 61.39, 62.50, and 62.57 (Å)³ for BFO, BSF, and BFS, respectively. X-ray photoelectron spectroscopy (XPS) study reveals that the chemical environments of Bi and Fe are different in BFO, BSF, BFS films. Similarly, XPS spectra for Sc2p lines in BSF and BFS also have different peak positions; this indicates Sc doping has certain chemical impact on BSF and BFS films. Systematic studies of Sc substitution along with the effect of annealing ambient on the dielectric constant (ε) and dielectric loss (tan δ), leakage current, remnant polarization (P_r), coercive field (E_c), and magnetic properties of the films are carried out. The room temperature values of ε and tan δ at 1 kHz for BFO and BFS films annealed in N₂ ambient are (∼208; 0.035) and (∼235; 0.023), respectively. The comparative value of leakage current for the BFO and BFS films at an applied field strength of 50 kV/cm are 2.997×10⁻⁴ and 1.87×10⁻⁵ A/cm², respectively. Room temperature value of coercive magnetization for BFS films has one order small compared to that of the BFO films; this indicates BFS films are magnetically soft and more suitable for potential device applications. Finally, among the studied compositions, the BFS films annealed in N₂ ambient show the best property.     

Crystal structure and properties of Bi1 ? x Ca x FeO3 and Bi1 ? x Ca x FeO1 ? x Ti x O3 solid solutions

Systems of solid solutions Bi_{1 − x} Ca _x FeO₃ (I) and Bi_{1 − x} CaxFeO_{1 − x} Ti _x O₃ (II) have been obtained and their properties have been studied using neutronography and M?ssbauer spectroscopy; magnetization and permittivity have been measured. It is shown that an increase in the concentration of calcium ions in system I for x > 0.2 changes rhombohedral distortions of a unit cell (space group R3c) to tetragonal distortions (space group I4/mcm), while rhombohedral distortions in system II for x > 0.2 are replaced by orthorhombic distortions (space group Pnma). Analysis of the crystal structure has revealed strong anisotropy in vibrations of Bi and O ions in system I compounds. Systems I and II are characterized by G-type antiferromagnetic ordering of magnetic moments. In system II, spontaneous magnetization associated with the Dzyaloshinskii-Moriya interaction has been detected. According to M?ssbauer spectroscopy data, iron ions in compounds I and II are in the trivalent state and charge compensation occurs due to the formation of oxygen vacancies. The permittivity increases with the calcium concentration. Original Russian Text ? I.O. Troyanchuk, D.V. Karpinsky, M.V. Bushinskii, O. Prokhnenko, M. Kopcevicz, R. Szymczak, J. Pietosa, 2008, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2008, Vol. 134, No. 1, pp. 105–112.     

Effect of oxygen deficiency on the magnetic, electrical, magnetoelectric, and magnetoelastic properties of La1 ? x Sr x MnO3 ? δ manganites

This paper reports on a study of the effect of oxygen deficiency on the magnetic and electrical properties of the La_{1 − x} Sr _x MnO_{3 − δ} manganites (x = 0, 0.2, 0.4; δ = 0, 0.13, 0.2). In compositions with x = 0 and δ = 0.13 and 0.2, the temperature dependence of the magnetization M (T) can be approximated by the Langevin function with the moment of superparamagnetic clusters μ = 77μ_B (δ = 0.13) and 86μ_B (δ = 0.2) at temperatures of 25 K ≤ T ≤ 250 K, with the exception of a small temperature range near 132 K in which a maximum characteristic of the LaMnO₃ antiferromagnet is seen. These compositions, as well as Sr-doped compositions with δ ≠ 0, reveal a difference between the magnetizations of the sample cooled in a weak magnetic field and in zero field. At T = 6 K in a magnetic field of 16 kOe, the compositions with x = 0.2 and 0.4, δ = 0.13 possess a magnetic moment per formula unit lower than that with δ = 0, as well as reveal an anomalous relation between the Curie temperature T _C and the Curie paramagnetic point gJ, namely, T _C > gJ. The magnetization of compositions with x = 0.2 and 0.4, δ = 0.2 follows the Langevin function with μ = 40μ_B and 130μ_B, respectively. The electrical resistivity of samples with x = 0.4 and δ = 0.13 and 0.2 is one to two orders of magnitude larger than that of the composition with x = 0.4, δ = 0, which evidences partial or complete compensation of acceptor defects (Sr²⁺ ions) by donor defects (doubly charged O²⁻ vacancies). The above properties of oxygen-deficient compositions suggest that they contain an insulating ferro-antiferromagnetic magnetically double-phase state. The magnetoresistance and volume magnetostriction in samples with x = 0.4 and δ = 0, 0.13, and 0.2 are small; indeed, in a magnetic field of 8 kOe, they do not exceed 1.4% and 6 × 10⁻⁶, respectively. On this basis, it is concluded that the unbalanced doubly charged donors (O vacancies) are in the state with antiparallel spins and, thus, do not initiate the formation of ferron-type ferromagnetic clusters. The significance of both compensated and unbalanced doubly charged donors consists in that they give rise to the formation of fractured Mn-O-Mn bonds, which bring about lowering of the magnetic moment per formula unit in compositions with x = 0.2 and 0.4 and δ = 0.13 and the transition to superparamagnetism in compositions with x = 0.2 and 0.4, δ = 0.2. Original Russian Text ? L.I. Koroleva, D.M. Zashchirinskiĭ, T.M. Khapaeva, L.I. Gurskiĭ, N.A. Kalanda, V.M. Trukhan, R. Szymczak, B. Krzumanska, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 12, pp. 2201–2205.     

Ferroelectric phase stabilization, phase transformations and?thermal properties in (1? x )PbZrO3– x Pb(Co1/3Nb2/3)O3 solid solution

The solid solution between the antiferroelectric PbZrO₃ (PZ) and relaxor ferroelectric Pb(Co_1/3Nb_2/3)O₃ (PCoN) was synthesized by the columbite method. The phase structure and thermal properties of (1−x)PZ–xPCoN, where x=0.0–0.3, were investigated. With these data, the ferroelectric phase diagram between PZ and PCoN has been established. The crystal structure data obtained from XRD indicates that the solid solution PZ–PCoN, where x=0.0–0.3, successively transforms from orthorhombic to rhombohedral symmetry with an increase in PCoN concentration. The AFE→FE phase transition was found in the compositions of 0.0≤x≤0.10. The AFE→FE phase transition shift to lower temperatures with higher compositions of x. The width of the temperature range of FE phase was increased with increasing amount of PCoN. It is apparent that the replacement of the Zr⁴⁺ ion by (Co_1/3Nb_2/3)⁴⁺ ions would decrease the driving force for antiparallel shift of Pb²⁺ ions, because they interrupt the translational symmetry. This interruption caused the appearance of a rhombohedral ferroelectric phase when the amount of PCoN was more than 10 mol%.     

Dependences of the dielectric and pyroelectric properties of (1 ? x)PbFe1/2Nb1/2O3?xPbTiO3 ferroelectric ceramics solid solutions on the PbTiO3 content in a compositional range of 0 ≤ x ≤ 0.08

(1 − x)PbFe_1/2Nb_1/2O_3−x PbTiO₃ (PFN-xPT) ferroelectric ceramics with low dielectric loss and pronounced anomalies of dielectric and pyroelectric properties near the ferroelectric-ferroelectric phase transition was obtained by doping with lithium. The temperature dependence of the position of the morphotropic boundary between the rhombohedral (monoclinic) and tetragonal phases in the x-T phase diagram of the PFN-xPT system was determined for the first time.     

Anomalies of the pyroelectric and dielectric properties of ferroelectric ceramics of the PbZr1- x Ti x O3 system with 0.06 ≤ x ≤ 0.35 at the R3 c ? R 3 m phase transition

The temperature dependences of the pyroelectric and dielectric properties of ferroelectric ceramics of the PbZr_{1 − x} Ti _x O₃ binary system with x = 0.06, 0.07, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.35 have been obtained synchronously for each sample in the range of the structural phase transition between the states with the symmetry space groups R3c ↔ R3m. It is established that the temperatures of this phase transition for unpolarized and polarized samples coincide in the range 0.06 ≤ x ≤ 0.15. In this case, the x−T phase diagram, constructed on the basis of the pyroelectric and dielectric data, is in excellent agreement with the X-ray diffraction data on single crystals in this concentration range. The effect of dc electric fields from 5 × 10⁵ V m⁻¹ did not lead to any temperature shifts of the R3c ↔ R3m phase transition for the compositions with 0.06 ≤ x ≤ 0.25. Original Russian Text ? Yu.N. Zakharov, A.G. Lutokhin, N.A. Korchagina, V.G. Kuznetsov, 2008, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2008, Vol. 72, No. 4, pp. 589–591.     

Effect of polarization on the intensity of anomalous electron emission in the (1 ? x)PbMg1/3Nb2/3O3 + xPbTiO3 system

Spectra of anomalous electron emission from the surface of solid solutions in the (1 − x)PbMg_1/3Nb_2/3O₃ + xPbTiO₃ system with x = 0.06, 0.10, 0.13, 0.20, and 0.25 have been studied. While the energy characteristics of the anomalous electron emission spectra vary monotonically with x, the behavior of integrated intensity was found to be nonmonotonic with a maximum occurring at x = 0.1. According to the proposed interpretation, the results obtained are explained by the effect of the potential barrier on the electron emission; the potential barrier depends, in turn, on the permittivity ε of the samples. Original Russian Text ? A.T. Kozakov, A.V. Nikol’skiĭ, V.P. Sakhnenko, A.N. Pavlov, V.G. Smotrakov, V.V. Eremkin, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 7, pp. 1310–1314.     

Magnetic, electrical, and optical properties of Ca1 ? x Ce x MnO3 ( x ≤ 0.12) single crystals

The magnetic, electrical, and optical properties of Ca_{1 − x} Ce _x MnO₃ (x≤0.12) manganite single crystals are investigated with the aim of revealing the specific features of the multiphase electronic and magnetic state as a function of the cerium concentration and the atmosphere used for growing single crystals. It is found that the concentration dependence of the low-temperature magnetization M(x) of the single crystals is shifted toward the high-concentration range as compared to the corresponding dependence of the polycrystals, which is explained by the predominant cation deficiency. The electrical resistivity and the reflection spectra of the single crystals in the infrared spectral range indicate that charge carriers exhibit a band nature at temperatures close to room temperature. The temperature dependence of the electrical resistivity of the single crystal with x = 0.08, which has the maximum magnetization in the studied series of Ca_{1 − x} Ce _x MnO₃ compounds, unlike polycrystals, exhibits a metallic behavior over the entire temperature range. The G-type antiferromagnetic phase with the Néel and Curie temperatures T _N(G) = T _C = 100 K is characterized by maxima of the electrical resistivity ρ and the magnetoresistance Δρ/ρ = |(ρ₀ − ρ _H )/ρ₀| = 38% in the magnetic field H = 90 kOe. The magnetoresistance Δρ/ρ of the single crystals at cerium concentrations x = 0.10 and 0.12 with variations in temperature exhibit three specific features: near the temperature of charge ordering T _co, near the temperature of the magnetic phase transition to the C-type antiferromagnetic phase T _N(C), and near the temperature of the phase transition to the magnetic charge-ordered phase T _N(MCO). An anomalous temperature dependence of the magnetization is revealed for a single crystal with x = 0.10 grown in oxygen at a pressure of 5 atm, which is explained by the presence of regions with hole conductivity due to cation deficiency. The inhomogeneous electronic and magnetic state is associated with the interrelation of the charge, orbital, and spin orderings. Original Russian Text ? N.N. Loshkareva, A.V. Korolev, N.I. Solin, E.V. Mostovshchikova, S.V. Naumov, N.V. Kostromitina, A.M. Balbashov, 2009, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2009, Vol. 135, No. 1, pp. 98–107.     

Effect of excess oxygen on the electrical and magnetic properties of La1 ? xAgxMnO3 (x = 0.05, 0.1, 0.2) at 77 K < T < 300 K

A study has been made of the magnetic and electrical properties of oxygen-enriched La_{1 − x} Ag _x MnO_3.1 manganites at 77 K < T < 300 K. The samples have been produced by the sol-gel technique. The study has revealed an increase of the Curie temperature and a shift of the maximum in magnetoresistance toward high temperatures.     

Investigation of the influence of gradual substitution K ? Rb on the structure and phase transition in K x Rb1 ? x Pb2Br5 solid solutions

Single crystals of K _x Rb_{1 − x} Pb₂Br₅ solid solutions have been grown and investigated using X-ray diffraction and polarized light microscopy in the temperature range 270–640 K. The regions of existence of the tetragonal (I4/mcm) and monoclinic (P2₁/c) phases have been determined. It has been demonstrated that the partial introduction of rubidium into KPb₂Br₅ leads to an increase in the temperature of the ferroelastic phase transition (P2₁/c↔mmm), so that it approaches the melting temperature. In the solid solutions with x ≈ 0.4−0.5, the temperature region of existence of the orthorhombic phase is narrowed to ≈ 1−2 K. It has been revealed that an increase in the potassium content in the material results in a considerable increase in the incorporation coefficient of Er³⁺ ions. Original Russian Text ? L.I. Isaenko, S.V. Mel’nikova, A.A. Merkulov, V.M. Pashkov, A.Yu. Tarasova, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 554–557.     

Optical properties of the HfO2 ? x N x and TiO2 ? x N x films prepared by ion beam sputtering

Optical characteristics of the HfO_{2 − x} N _x and TiO_{2 − x} N _x films obtained by reactive ion beam sputtering have been investigated by spectral ellipsometry. The chemical composition of the films was determined using X-ray photoelectron spectroscopy. The nitrogen content in the oxynitride films (determined by the N₂/O₂ ratio in the gas mixture during synthesis) reached ≈9 at % for TiO_{2 − x} N _x and ≈ 6 at % for HfO_{2 − x} N _x . It is found that the dispersion relations n(λ) and k(λ) for the TiO_{2 − x} N _x films change from those characteristic of titanium dioxide to those typical of titanium nitride with an increase in the nitrogen content from 0 to ≈9 at %. The optical parameters of the HfO_{2 − x} N _x films depend weakly on the nitrogen content in the range 0–6 at %. Original Russian Text ? V.V. Atuchin, V.N. Kruchinin, A.V. Kalinkin, V.Sh. Aliev, S.V. Rykhlitskiĭ, V.A. Shvets, E.V. Spesivtsev, 2009, published in Optika i Spektroskopiya, 2009, Vol. 106, No. 1, pp. 77–82.     

Effect of high pressure and chemical substitution on the crystal structure and magnetic state of R2Fe17 ? xSix (R = Lu or Y; x = 0 or 1.7)

The effect of high pressure on the crystal structure of the intermetallic compounds R₂Fe_{17 − x} Si_x (R = Lu or Y; x = 0 or 1.7) was studied using neutron diffraction. A correlation between changes in structural parameters and magnetic properties under the action of high pressure, as well as under chemical substitution of Si for Fe atoms, was analyzed in terms of localized moment and spin fluctuation models. The spin fluctuation model was found to describe more adequately the experimentally observed increase in the Curie temperature upon chemical substitution and the decrease in this temperature under the action of high pressure. Possible reasons for the suppression of a collinear ferromagnetic state and the occurrence of a noncollinear antiferromagnetic state in R₂Fe_17−x Si_x under pressure are discussed based on estimated differences between the total energy minima of these states.     

Dimension effects on the dielectric properties of fine BaTiO3 ceramics

It is found that the core-shell structured grains are easy to produce for fine grain doped BaTiO3 ceramics in the sintering process. We study the influence of the core-shell structure on the Curie–Weiss temperature and dielectric properties of BaTiO3 ceramics by using effective medium approximation(EMA). Considering the second approximation, the dielectric properties of fine grain doped BaTiO3 ceramics are consistent with experimental data.     

Phase x-T diagram of actual solid solutions of the (1 ? x )PbZrO3- x PbTiO3 system (0.37 ≤ x ≤ 0.57)

Ceramics of PbZr_{1 − x} Ti _x O₃ solid solutions were systematically studied in the range 0.37 ≤ x ≤0.57. The x-T phase diagram of the system is constructed in the range 25°C ≤ T ≤ 650°C. The diagram has a region of an indefinite symmetry in the vicinity of the transition to the nonpolar cubic phase. It is established that solid solutions in this region are characterized by weak distortions and temperature-time instability of the crystal structure. Three concentration regions are separated differing in the value of the jump in the unit cell volume ΔV at the line of transitions from the rhombohedral (tetragonal) phase to the region of indefinite symmetry. It is revealed that there are three temperature ranges differing in the behavior of the temperature dependence of the inverse permittivity, which are due to the existence of two critical Curie points at the boundary separating the ferroelectric phases from the cubic phase. Original Russian Text ? L.A. Reznichenko, L.A. Shilkina, O.N. Razumovskaya, E.A. Yaroslavtseva, S.I. Dudkina, O.A. Demchenko, Yu.I. Yurasov, A.A. Esis, I.N. Andryushina, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 8, pp. 1469–1475.     

Influence of cobalt on the structural and magnetic Inhomogeneities, phase transitions, and magnetoresistive properties of La0.6Sr0.2Mn1.2 ? x Co x O3 ± δ

The structure and properties of magnetoresistive ceramics La_0.6Sr_0.2Mn_{1.2 − x} Co _x O3 ± δ (x = 0−0.3) sintered at a temperature of 1200°C are investigated using x-ray diffraction, resistance, and magnetic (χ _ac , M, ⁵⁵Mn NMR) measurements. It is shown that the samples contain the rhombohedral (R c) perovskite (90%) and tetragonal (I4₁/amd) hausmannite (10%) phases. The lattice parameters of these phases decrease with an increase in the cobalt content x. The real perovskite structure involves point defects (anion and cation vacancies) and nanostructured defects of the cluster type. An analysis of the asymmetrically broadened ⁵⁵Mn NMR spectra confirms the high-frequency electron-hole exchange between Mn³⁺ and Mn⁴⁺ ions and a local inhomogeneity of their environment by other ions and defects of the point and cluster types. An increase in the Co content leads to an increase in the electrical resistivity, an enhancement of the magnetoresistance (MR) effect, and a decrease in the magnetic susceptibility and the temperatures of the metal-semiconductor (T _ms ) and ferromagnetic-paramagnetic (T _C) phase transitions due to the suppression of the exchange interaction between Mn³⁺ and Mn⁴⁺ ions by vacancies and clusters. The introduction of cobalt results in a decrease in the ferromagnetic component and the activation energy. The magnetoresistance effect in the vicinity of the phase transition temperatures T _ms and T _C is associated with the scattering of charge carriers from intracrystallite inhomogeneities of the lattice, and the low-temperature magnetoresistance effect is governed by the tunneling at the intercrystalline boundaries. Original Russian Text ? A.V. Pashchenko, V.P. Pashchenko, A.A. Shemyakov, N.G. Kisel’, V.K. Prokopenko, Yu.F. Revenko, A.G. Sil’cheva, V.P. Dyakonov, H. Szymczak, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 7, pp. 1257–1262.     

Effect of fuel on the formation structure,transport and magnetic properties of LaMnO3+ δ nanopowders

Single-step low-temperature solution combustion (LCS) synthesis was adopted for the preparation of LaMnO_{3+ δ} (LM) nanopowders. The powders were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), surface area and Fourier transform infrared spectroscopy (FTIR). The PXRD of as-formed LM showed a cubic phase but, upon calcination (900°C, 6 h), it transformed into a rhombohedral phase. The effect of fuel on the formation of LM was examined, and its structure and magnetoresistance properties were investigated. Magnetoresistance (MR) measurements on LM were carried out at 0, 1, 4 and 7 T between 300 and 10 K. LM (fuel-to-oxidizer ratio; ψ = 1) showed an MR of 17% at 1 T, whereas, for 4 and 7 T, it exhibited an MR of 45 and 55%, respectively, near the T _M-I. Metallic resistivity data below T _M-I showed that the double exchange interaction played a major role in this compound. It was interesting to observe that the sample calcined at 1200°C for 3 h exhibited insulator behavior.     

Novel synthesis of NixZn1?xFe2O4 (0?≤?x?≤?1) nanoparticles and their dielectric properties

Nanocrystalline Ni _x Zn_1−x Fe₂O₄ (0 ≤ x ≤ 1) ferrite powders with average particle size 15–20 nm have been successfully prepared at a very low temperature (180 °C) by a novel auto combustion process using citric acid and ethylenediamine as a coordinating agent and bridging ligand, respectively. Phase purity of the solid solutions has been confirmed by X-ray diffraction. Morphological characterizations of the prepared samples were performed by high resolution transmission electron and field emission scanning electron microscopy. Extensive Fourier transformed infrared spectroscopic characterization has been carried out to identify the plausible mechanism of the synthesis process. Composition-dependent electrical properties (resistivity and dielectric constant) of the synthesized solid solution have been investigated. Interestingly, a non-linear variation of dielectric permittivity with respect to composition has been observed. The room temperature electrical resistivity as well as the dielectric permittivity of Ni_0.5Zn_0.5Fe₂O₄ was found to decrease with the decrease of particle size.