Maxwell–Wagner relaxation and magnetodielectric properties of Bi<Subscript>0.5</Subscript>La<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> ceramics

The complex permittivity ε = ε′–iε″ of manganite bismuth–lanthanum Bi_0.5La_0.5MnO₃ ceramics has been measured at temperature T = 78 K in the frequency range f = 200–10⁵ Hz and in the magnetic induction range B = 0–5 T. Dielectric relaxation and the pronounced magnetodielectric effect have been detected. The explanation based on the superposition of Maxwell–Wagner relaxation and the magnetoresistance effect has been proposed.     

High resolution diffraction and small angle scattering neutron investigations of LaCo<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>O<Subscript>3+</Subscript><Subscript>δ</Subscript>: effect of oxygen content

We have investigated LaCo_0.5Mn_0.5O_{3+ δ} compounds with different oxygen content by means of magnetization, high resolution and small-angle neutron diffraction measurements. Oxygen content decrease down to stoichiometric composition leads to an essential increase of T_C and magnetic moment while Co/Mn ionic ordering degree is kept almost constant. It is assumed that upon oxygen reduction Co³⁺ ions change their valence state down to 2+ one that leads to dominating of Co²⁺-Mn⁴⁺ ferromagnetic interactions as well as T_C increase. Magnetic properties can be explained in terms of coexistence of long-range ferromagnetic order and short-range clusters with antiferromagnetic interactions prevailing. Size distribution of the mentioned short-range magnetic inhomogeneities is rather mild within the samples but it is strongly temperature dependent.     

Microwave characterization of Pb<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> multiferroics at X-band

The microwave characteristics of Pb_1?x Ca _x Fe_0.5Nb_0.5O₃ multiferroics (x = 0.0, 0.4, 0.45, 0.5, 0.55, 0.6), have been investigated as a function of frequency and substitution. The results depict ?13.99 dB reflection loss at 11.65 GHz in composition x = 0.6. Microwave absorption is enhanced with substitution of Ca²⁺ ions and undoped composition 0.0 behaves as electromagnetic shield. The model governing microwave absorption is discussed and different compositions for electromagnetic applications have been suggested.     

Orientation dependence of electrical properties of 0.96Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-0.04BaTiO<Subscript>3</Subscript> lead-free piezoelectric single crystal

In this paper, a single crystal of 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ with dimensions of Φ 30×10 mm was grown by the top-seeded-solution growth method. X-ray powder diffraction results show that the as-grown crystal possesses the rhombohedral perovskite-type structure. The dielectric, piezoelectric and electrical conductivity properties were systematically investigated with 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples. The room-temperature dielectric constants for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples are found to be 650, 740 and 400 at 1 kHz. The (T _m, ε _m) values of the dielectric temperature spectra are almost independent of the crystal orientations; they are (306°C, 3718), (305°C, 3613) and (307°C, 3600) at 1 kHz for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal. The optimum poling conditions were obtained by investigating the piezoelectric constants d ₃₃ as a function of poling temperature and poling electric field. For the 〈001〉 and 〈110〉 crystal samples, the maximum d ₃₃ values of 146 and 117 pC/N are obtained when a poling electric field of 3.5 kV/mm and a poling temperature of 80°C were applied during the poling process. The as-grown 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ crystal possesses a relatively large dc electrical conductivity, especially at higher temperature, having a value of 1.98×10⁻¹¹ Ω⁻¹⋅m⁻¹ and 3.95×10⁻⁹ Ω⁻¹⋅m⁻¹ at 25°C and 150°C for the 〈001〉 oriented crystal sample.     

Large electrostrictive strain in lead-free Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–KNbO<Subscript>3</Subscript> ceramics

In the present work, (1−x)(0.935Bi_0.5Na_0.5TiO₃–0.065BaTiO₃)–xKNbO₃ (BNT–BT–KN, BNT–BT–100xKN) ceramics with x ranging from 0 to 0.1 were prepared by the conventional ceramic fabrication process. A large electrostrictive coefficient of ∼10⁻² m⁴ C⁻² is obtained with the composition x ranging from 0.02 to 0.1, which is close to the well-known electrostrictive material Pb(Mg_1/3Nb_2/3)O₃. Under an electric field of 4 kV/mm, the electrostrictive strain can reach as high as 0.08%. Besides, the electric field induced strain behavior indicates a temperature independent behavior within the temperature range of 20 to 150°C. The large electrostrictive strain is suggested to be ascribed to the formation of non-polar (NP) phase developed by the KNbO₃ substitution, and the high electrostrictive coefficient of BNT–BT–KN ceramics makes them great candidates to be applied in the new solid-state actuators.     

An ab initio study of PuO<Subscript>2±0.25</Subscript>, UO<Subscript>2±0.25</Subscript>, and U<Subscript>0.5</Subscript>Pu<Subscript>0.5</Subscript>O<Subscript>2±0.25</Subscript>

Hybrid density functional theory has been used to systematically study the electronic, geometric, and magnetic properties of strongly correlated materials PuO_2±x , UO_2±x , and U_0.5Pu_0.5O_2±x with x = 0.25. The calculations have been performed using the all-electron full- potential linearized augmented plane wave plus local orbitals basis (FP-L/APW+lo) method. Each compound has been studied at the ferromagnetic (FM) and anti-ferromagnetic (AFM) configurations with and without spin-orbit coupling (SOC) and full geometry optimizations. The optimized lattice constants, bulk moduli, and band gaps are reported. Total energy calculations indicate that the ground states are AFM for all compounds studied here and the band gaps are typically higher than 1.0 eV, characteristic of semiconductors. The total energy is lowered significantly and the band gaps increase with the inclusion of SOC. The chemical bonds between the actinide metals and oxygen atoms are primarily ionic in character.     

The low-temperature macroscopic phase separation in La<Subscript>0.5</Subscript>Ba<Subscript>0.5</Subscript>CoO<Subscript>3 − δ</Subscript> cobaltite

La_0.5Ba_0.5CoO_2.87 has been characterized with neutron and synchrotron powder diffraction and magnetization measurements. This compound was shown to have a cubic crystal structure at temperatures above 200 K whereas slightly above the Curie point T _c ∼ 170 K the structural separation into two different pseudocubic phases gradually develops upon cooling. The structural transformation is reversible. At 2 K the sample consists of G-type antiferromagnetic oxygen-poor and ferromagnetic oxygen-rich phases (approximately 33 and 66%, respectively).     

Actively Q-switched performance of a mixed crystal Nd:Lu<Subscript>0.5</Subscript>Y<Subscript>0.5</Subscript>VO<Subscript>4</Subscript> at 1.34 μm

The actively Q-switched laser performance of the mixed Nd:Lu_0.5Y_0.5VO₄ crystal was demonstrated for the first time. At the pump power of 7.26 W, the minimum pulse width of 46.6 ns was obtained at the pulse repetition rate of 5 kHz with the cavity length of 80 mm, and the single pulse energy and peak power were calculated to be 42 μJ and 901.3 W, respectively.     

Cluster spin glass and superparamagnetism in RuSr<Subscript>2</Subscript>Eu<Subscript>1.5</Subscript>Ce<Subscript>0.5</Subscript>Cu<Subscript>2</Subscript>O<Subscript>10-</Subscript><Subscript>δ</Subscript>

We investigate in detail the dc magnetization and nonlinear ac susceptibility behavior of the superconducting ferromagnet RuSr₂Eu_1.5Ce_0.5Cu₂O_{10- δ} (Ru1222) to develop a comprehensive understanding of the spin glass and superparamagnetism in this material. The structural properties of the system result in the formation of magnetic (ferromagnetic) clusters of different sizes, shapes and properties. The magnetic clustering of the system leads to observation of various features in dc magnetization and ac susceptibility consistent with superparamagnetism and cluster spin glass states, which can coexist or stand alone, depending on the temperature range considered. Experimental results of magnetic measurements in combination with their analysis have enabled us to explain and distinguish these phenomena, as well as to propose a temperature dependent scenario of the system behavior.     

<Superscript>2</Superscript>H NMR investigation of the transition to the proton glass state in the Cs<Subscript>5</Subscript>H<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript> · 0.5H<Subscript>2</Subscript>O crystal

A crystal of the Cs₅H₃(SO₄)₄ · xH₂O (x ≈ 0.5) (PCHS) compound, which belongs to the family of proton conductors with a complex system of hydrogen bonds, is investigated by ²H NMR spectroscopy. The temperature and orientation dependences of the ²H NMR spectra are measured and analyzed. It is established that, upon transition to the glassy phase at the temperature T _g = 260 K, the parameters characterizing the proton exchange between positions in hydrogen bonds remain unchanged to within the limits of experimental error. The protons in the two-dimensional network of hydrogen bonds in the (001) plane are dynamically disordered over possible positions down to temperatures considerably lower than the glass transition point T _g . However, water molecules are fixed at particular structural positions in the phase transition range. In PCHS crystals with a nonstoichiometric water content, this circumstance can be responsible for the frustration that leads to the formation of the glassy state.     

Successive structural phase transitions in Pr<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> in the range 10–1120 K

The crystal and magnetic structures of the Pr_0.5Sr_0.5CoO₃ metallic ferromagnet have been studied using neutron diffraction and synchrotron radiation. Successive structural transitions with the reduction of the crystal symmetry from cubic (space group Pm3m) to rhombohedral (\(R\bar 3c\), ～800 K), orthorhombic (Imma, ～300 K) and, then, to triclinic at ～120 K are detected during cooling from 1120 K. The transition from the orthorhombic system to a phase with a lower symmetry is characterized by a sharp change in the anisotropy of the unit cell, which indicates the partial ordering of the e _g orbitals of cobalt. The accompanying change in the interatomic distances and valence angles give rise to an anomaly in the temperature dependence of the magnetic susceptibility at T ≈ 120 K. The ordered magnetic moment μ_Co ≈ 2μ_B corresponds to the assumption of the intermediate spin state of Co³⁺ ions and the mixture of low- and intermediate-spin states of Co⁴⁺ ions.     

Role of iron in Na <Subscript>1.5</Subscript>Fe <Subscript>0.5</Subscript>Ti <Subscript>1.5</Subscript>(PO <Subscript>4</Subscript>) <Subscript>3</Subscript>/C as electrode material for Na-ion batteries studied by operando Mössbauer spectroscopy

The role of iron in Na _1.5Fe _0.5Ti _1.5(PO ₄)₃/C electrode material for Na batteries has been studied by ⁵⁷Fe Mössbauer spectroscopy in operando mode. The potential profile obtained in the galvanostatic regime shows three plateaus at different voltages due to different reaction mechanisms. Two of them, at 2.2 and 0.3 V vs Na ⁺/Na ⁰, have been associated to redox processes involving iron and titanium in Na _1.5Fe _0.5Ti _1.5(PO ₄)₃. The role of titanium was previously elucidated for NaTi ₂(PO ₄)₃ and the effect of the substitution of Fe for Ti was investigated with ⁵⁷Fe Mössbauer spectroscopy. We show that iron is an electrochemically active center at 2.2 V with the reversible Fe ³⁺/Fe ²⁺ transformation and then remains at the oxidation state Fe ²⁺ along the sodiation until the end of discharge at 0 V.     

μSR study of Eu<Subscript>0.8</Subscript>Ce<Subscript>0.2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>5</Subscript> and EuMn<Subscript>2</Subscript>O<Subscript>5</Subscript> multiferroics

A comparative μSR study of ceramic samples of the EuMn₂O₅ and Eu_0.8Ce_0.2Mn₂O₅ multiferroics is performed in the temperature range from 15 to 300 K. It is found that the Ce doping of the EuMn₂O₅ sample slightly reduces the temperature of the magnetic phase transition from T _N = 45 K for the EuMn₂O₅ sample to T _N = 42.5 K for the Eu_0.8Ce_0.2Mn₂O₅ sample. Below the temperature T _N for both samples, there are two types of localization of a thermalized muon with different temperature dependences of the precession frequency of the magnetic moment of the muon in an internal magnetic field. The higher frequency in both samples refers to the initial antiferromagnetic matrix. The behavior of this frequency in Eu_0.8Ce_0.2Mn₂O₅ follows the Curie–Weiss law with the exponent β = 0.29 ± 0.02, which differs from the value β = 0.39 standard for 3D Heisenberg magnetics and is observed in EuMn₂O₅, because of the strong frustration of the doped sample. The temperature-independent low frequency is due to the presence of Mn³⁺–Mn⁴⁺ ferromagnetic pairs located along the b axis of the antiferromagnetic matrix and in the regions of phase separation, which contain such ion pairs and e _g electrons recharging them. In both samples, polarization losses are the same (about 20%) and are associated with the formation of Mn⁴⁺–Mn⁴⁺ + Mu complexes near Mn³⁺–Mn⁴⁺ ferromagnetic pairs. In the temperature interval from 25 to 45 K, the separation of the Eu_0.8Ce_0.2Mn₂O₅ structure into two fractions where the relaxation rates of polarization of muons differ by an order of magnitude is revealed. This effect is due to a change in the state of regions of phase separation (1D superlattices) at the indicated temperatures. Such effect in EuMn₂O₅ is significantly weaker.     

High-Temperature Heat Capacity of Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>–Cu<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> Solid Solutions

Differential scanning calorimetry has been used to study the influence of temperature on the heat capacity of synthesized vanadates Zn₂V₂O₇, (Cu_0.56Zn_1.44)V₂O₇, and (Cu_1.0Zn_1.0)V₂O₇. It is found that dependences C_p = f(T) have extremes. The thermodynamic properties of Zn₂V₂O₇ have been determined.     

Mössbauer and magnetic studies of the phase state of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/La<Subscript>0.9</Subscript>Ca<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> composites

The formation of an intermediate phase in SrFe₁₂O₁₉/La_0.9Ca_0.1MnO₃ composites was demonstrated for the first time using only Mössbauer spectroscopy. The SrFe₁₂O₁₉/La_0.9Ca_0.1MnO₃ composite was prepared by the two-stage (sol–gel and hydrothermal) synthesis with varying initial conditions. The X-ray diffraction studies showed that the composite consisted of two phases: well-formed structures of manganite La_0.9Ca_0.1MnO₃ and hexagonal ferrite SrFe₁₂O₁₉. It was found that nanocrystalline La_0.9Ca_0.1MnO₃ particles with size d ? 150 nm formed in the composites at the surface of plate-like SrFe₁₂O₁₉ crystallites. The Mössbauer studies showed that the composite contained additional (intermediate) phase La_0.9Ca_0.1Mn(Fe)O₃ that formed at the interface between SrFe12O19 and La_0.9Ca_0.1MnO₃ phases. The intermediate phase concentration increased with the molar content of La_0.9Ca_0.1MnO₃; in this case, the fraction of the surface of SrFe₁₂O₁₉ crystallites coated with La_0.9Ca_0.1MnO₃ increased, which led to the increase in the total area of the interface surface and the intermediate phase concentration.     

Structural properties of composite cathode material LiFePO<Subscript>4</Subscript>–Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Composite cathode material LiFePO₄–Li₃V₂(PO₄)₃ is synthesized through a chemical reduction and lithiation using FeVO₄·xH₂O as both iron and vanadium sources. The structural properties of LiFePO₄–Li₃V₂(PO₄)₃ are investigated. X-ray diffraction results show the composite material containing olivine type LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ phases. High-resolution transmission electron microscopy and energy-dispersive X-ray spectrometry results indicate that mutual doping effects take place between the LiFePO₄ and Li₃V₂(PO₄)₃ particles with V³⁺ doping the LiFePO₄ while Fe²⁺ dopes the Li₃V₂(PO₄)₃. LiFePO₄–Li₃V₂(PO₄)₃ nanocomposites are formed in the carbon webs. There is no structural compatibility between monoclinic (Li₃V₂(PO₄)₃) and olivine (LiFePO₄) domains in composite material LiFePO₄–Li₃V₂(PO₄)₃.     

Magnetic and magnetoresistive properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sr<Subscript>2</Subscript>FeMoO<Subscript>6–δ</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoheterostructures

A method has been developed for fabricating nanoporous matrices based on anodic aluminum oxide for the deposition of ferromagnetic nanoparticles in them. The modes of deposition of strontium ferromolybdate thin films prepared by the ion-plasma method have been worked out, and the magnetic and magnetoresistive properties, structure, and composition of the films have been investigated. It has been revealed that the microstructure and properties of the strontium ferromolybdate films deposited by ionplasma sputtering depend on the deposition rate and the temperature of the substrate. Based on the measurement of the electrical resistivity of nanoheterostructures in a magnetic field, it has been found that the magnetoresistance reaches 14% at T = 15 K and B = 8 T, which is due to the manifestation of tunneling magnetoresistance.     

Gd-doped SrTi<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>O<Subscript>3–δ</Subscript> mixed ionic-electronic conductors: structural,thermal, and electrical properties

The effect of Sr by Gd substitution on the structural, thermomechanical, electrical, and electrochemical properties of SrTi_0.5Fe_0.5O_3–δ was investigated in the present work. The powders were synthesized by a solid-state reaction method at 1150 °C with following sintering of the ceramic samples at 1350 °C. The unit cell parameters of the sintered Sr_1–x Gd _x Ti_0.5Fe_0.5O_3–δ (x = 0–0.4) ceramics were found to decrease with a gradual increase in Gd content, and a change in the crystal symmetry from cubic to tetragonal at x ≥ 0.1 was observed. It was found that the Gd doping enhanced the stability of the ceramic samples in a reducing atmosphere and reduced the thermal expansion coefficient value. Gd doping in the amount of 5 mol% can be used for long-term stabilization of the SrTi_0.5Fe_0.5O_3–δ material’s conductivity in reducing atmospheres with no significant alteration to the transport properties and oxygen permeability.     

Preparation and characterization of organic–inorganic hybrid compound [N(C<Subscript>4</Subscript>H<Subscript>9</Subscript>)<Subscript>4</Subscript>]<Subscript>2</Subscript>Cu<Subscript>2</Subscript>Cl<Subscript>6</Subscript>

Organic–inorganic hybrid sample [N(C₄H₉)₄]₂Cu₂Cl₆ was prepared via the reaction between copper chloride and tetrabutylammonium chloride. The compound was characterized by X-ray powder diffraction, IR, Raman, differential scanning calorimetry (DSC), DTA-TGA analysis and electrical impedance spectroscopy. DSC studies indicate a presence of one-phase transition at 343 K. The complex impedance of compound [N(C₄H₉)₄]₂Cu₂Cl₆ have been investigated in temperature and frequency ranges 300–380 K and 200 Hz–5 MHz, respectively. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit model. The circuits consist of the parallel combination of bulk resistance R _p and constant phase elements CPE. The frequency dependence of the conductivity is interpreted in term of Jonscher's law: s(w) = s_dc + Awⁿ \sigma (\omega ){ } = {\sigma_{\rm{dc}}} + { }A{\omega^n} . The conductivity follows the Arrhenius relation. The variation of the value of these elements with temperatures confirmed the availability of the phase transition at 343 K detected by DSC and electrical measurements.     

Low-temperature behavior of specific heat curves in ruthenocuprate RuSr<Subscript>2</Subscript>Gd<Subscript>1.5</Subscript>Ge<Subscript>0.5</Subscript>Cu<Subscript>2</Subscript>O<Subscript>10 − δ</Subscript>: Superconducting,magnetic and crossing-point effects

Magnetic and superconducting properties of polycrystalline samples of RuSr₂Gd_1.5Ce_0.5Cu₂O_{(10 − δ)}, asprepared (by solid-state reaction) and annealed in pure oxygen at different pressure are presented. Specific heat and magnetization were investigated in the temperature range 1.8–300 K with a magnetic field up to 8 T. Specific heat, C (T), shows a jump at the superconducting transition (with onset at T ≈ 37.5 K) and a Schottky-type anomaly below 20 K. It is found that curves C(T) taken for different values of magnetic field have the same crossing point (at T _* ≈ 2.7 K) for all samples studied. At the same time, C(H) curves taken for different temperatures have a crossing point at a characteristic field H _* ≈ 3.7 T. These effects are manifestations of the crossing-point phenomenon, which is supposed to be inherent for strongly correlated electron systems.