Magnetic phases in Pr0.5Sr0.5Mn1 ? xCoxO3 (x ≤ 0.5) solid solutions

The magnetic and magnetotransport properties of Pr_0.5Sr_0.5Mn_{1 − x} Co _x O₃ (x ≤ 0.5) solid solutions have been investigated using neutron diffraction methods. The magnetization and electrical conductivity have been measured in magnetic fields up to 140 kOe. It has been established that, during cooling in the temperature range from 160 to 110 K, the compounds of compositions with a cobalt content x ≤ 0.07 undergo a structural phase transition from the high-temperature ferromagnetic phase to the antiferromagnetic phase. A further substitution of cobalt for manganese leads to a stabilization of the inhomogeneous dielectric ferromagnetic state, whereas a state of the cluster spin-glass type has been revealed in compositions with x = 0.15 and 0.20. At x ≥ 0.25, a new magnetic phase with a Curie temperature up to 210 K is formed as a result of the magnetic interaction between manganese and cobalt ions. A magnetic phase diagram of the system under investigation has been constructed.     

Phase transformations and magnetotransport properties of the Pr0.5Sr0.5Co1 ? xMnxO3 system

The structural, magnetic, and magnetotransport properties of Pr_0.5Sr_0.5Co_{1 − x} Mn _x O₃ (x < 0.65) perovskites are studied by magnetization and electrical conductivity measurements in magnetic fields up to 14 T and by neutron diffraction. In the manganese concentration range x < 0.5 and T = 300 K, the crystal structure is described by monoclinic space group I2/a; at x > 0.5, it is described by orthorhombic space group Imma. When the temperature decreases, a structural transformation without changing the symmetry takes place in all compounds. This transformation is caused by an active role of the inner shells of the praseodymium ion in chemical bond formation. The substitution of manganese for cobalt breaks a long-range ferromagnetic order near x ≈ 0.25, and a metal-dielectric transition occurs at x ≈ 0.15. The negative magnetoresistance is found to be maximal near a critical manganese concentration, where a long-range magnetic order is broken; it reaches 95% in a field of 14 T at T = 10 K for x = 0.2. An unusual dielectric magnetic state with a small spontaneous magnetic moment and a sharp transition into a paramagnetic state at T > 200 K is revealed in the concentration range 0.30 ≤ x ≤ 0.65 in spite of the absence of coherent magnetic neutron scattering. A model is proposed to explain the behavior of the magnetic properties in this phase.     

Bi0.5Ca0.5Mn1-xCoxO3体系中的电荷有序和相分离

利用固相反应法制备了Bi_0.5Ca_0.5Mn_1-xCo_xO₃(0≤x≤0.12)系列多晶样品.研究了Co掺杂对Bi_0.5Ca_0.5MnO₃电荷有序的影响.结果表明,Co掺杂导致电荷有序相逐渐融化、铁磁相互作用的增强;当x≥0.08时,电荷有序转变峰完全消失,但残留的反铁磁电荷有 关键词： 钙钛矿锰氧化物 电荷有序 团簇玻璃 相分离     

Structure, ferroelectric and piezoelectric properties of?(Bi0.98?xLa0.02Na1?x)0.5BaxTiO3 lead-free ceramics

Lead-free (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction show that La²⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi_0.5Na_0.5TiO₃ ceramics, the (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics possess much smaller coercive field E _c and larger remanent polarization P _r. Because of the low E _c (3.38 kV/mm), large P _r (46.2 μC/cm²) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d ₃₃=181 pC/N and k _p=36.3%. The depolarization temperature T _d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T _d.     

M?ssbauer study of compounds of Cu3 ? xFexSnS4 and Cu2Fe1 ?xZnxSnS4 systems

A M?ssbauer study of the structural and charge states of ⁵⁷Fe and ¹¹⁹Sn atoms in the compounds of Cu_{3 −x} Fe _x SnS₄ and Cu₂Fe_{1 − x} Zn _x SnS₄ systems was performed. It was shown that the iron atoms in the compounds of both systems were in the divalent and trivalent states occupying the tetrahedral positions of the structure. The character of the changes of the degree of covalency of the Fe²⁺-S, Fe³⁺-S and Sn⁴⁺-S bonds during the isomorphic substitution in the systems was established.     

p型Ag0.5(Pb8－xSnx)In0.5Te10化合物的制备及其热电性能

采用高温熔融缓冷和放电等离子烧结工艺制备了p型Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀五元化合物.研究了Sn含量对化合物载流子传输特性及热电性能的影响规律.结果表明：在Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀(x 关键词： 0.5(Pb_8-xSn_x)In_0.5Te₁₀')" href="#">Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀ 合成 载流子 热电性能     

Study of high-temperature oxygen permeability in Sr1 ? xLaxCo0.8 ? yNbyFe0.2O3 ? z perovskites

The oxygen permeability of ceramic SrCo_{0.8 − y} Fe_0.2Nb _y O_{3 − z} (0 ≤ y ≤ 0.2) and La_0.3Sr_0.7Co_0.6Fe_0.2Nb_0.2O_{3 − z} disc membranes as a function of temperature and oxygen partial pressure was studied. Kinetic analysis was performed based on the experimental data on oxygen permeability as a function of oxygen partial pressure.     

Low-temperature electrical conductivity and the superconductor-insulator transition induced by indium impurity states in (Pb0.5Sn0.5)1 ? xInxTe solid solutions

A study is reported of the low-temperature electrophysical (including superconducting) characteristics of the (Pb_0.5Sn_0.5)_{1 − x} In _x Te semiconducting solid solutions with an indium content variable within x = 0.05–0.20. A decrease in the impurity content x in the material has been found to bring about a decrease in the superconducting transition temperature T _c and the onset of an “insulating” state of the material. These effects manifest themselves in an increase in the low-temperature (T = 4.2 K) resistivity of (Pb_0.5Sn_0.5)_0.95In_0.05Te by more than three orders of magnitude as compared to that of (Pb_0.5Sn_0.5)_0.8In_0.2Te. A decrease in the In content in the solid solution also gives rise to a radical change in the shape of the temperature dependence of the electrical resistivity from a metallic behavior in the material with x = 0.20 (decrease in the electrical resistivity with decreasing temperature in the range 300–4.2 K) to a semiconducting behavior in a sample with x = 0.05 (exponential increase in the resistivity at T < 25 K). This transition to the insulating state with decreasing content of the impurity should be assigned to the displacement of the impurity band of quasi-local indium states toward the top of the light-hole valence band of the material and its emergence into the band gap of the solid solution.     

Elektronen-Spin-Resonanz an (La1??xGdyCex)Al2

In the EPR of (La_1––x Gd _y Ce _x )Al₂ a bottleneck in the relaxation of the conduction electrons to the lattice is present at sufficiently high Gd-concentrations. The bottleneck can be broken by decreasing the Gd-concentration or by adding Cerium as a spin-flip-scatterer.g-factor and line broadening are measured for (La_1–y Gd _y )Al₂ and (La_1––x Gd _y Ce _x )Al₂ as a function of temperature and Gd- and Ce-concentrations. The Cerium induced relaxationsrate _eL (Ce) increases linearly with Ce-concentration up tox0.025. This corresponds to the fact, well known by measurements of the Kondo anomalies, that Cerium impurities show no significant interaction up to rather high concentrations.     

Structure, electrical properties and temperature characteristics of?Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Bi0.5Li0.5TiO3 lead-free piezoelectric ceramics

(1−x−y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃– yBi_0.5Li_0.5TiO₃ lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique, and their structure, electrical properties, and temperature characteristics have been studied systematically. The ceramics can be well-sintered at 1050–1150 °C. The increase in K⁺ concentration decreases the grain-growth rate and promotes the formation of grains with a cubic shape, while the addition of Li⁺ decreases greatly the sintering temperature and assists in the densification of BNT-based ceramics. The results of XRD diffraction show that K⁺ and Li⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure. As x increases from 0.05 to 0.50, the ceramics transform gradually from rhombohedral phase to tetragonal phase and consequently a morphotropic phase boundary (MPB) is formed at 0.15≤x≤0.25. The concentration y of Li⁺ has no obvious influence on the crystal structure of the ceramics. Compared with pure Bi_0.5Na_0.5TiO₃, the partial substitution of K⁺ and Li⁺ for Na⁺ lowers greatly the coercive field E _c and increases the remanent polarization P _r of the ceramics. Because of the MPB, lower E _c and large P _r, the piezoelectricity of the ceramics is improved significantly. For the ceramics with the compositions near the MPB (x=0.15–0.25 and y=0.05–0.10), the piezoelectric properties become optimum: piezoelectric coefficient d ₃₃=147–231 pC/N and planar electromechanical coupling factor k _P=20.2–41.0%. In addition, the ceramics exhibit relaxor characteristic, which probably results from the cation disordering in the 12-fold coordination sites. The depolarization temperature T _d shows a strong dependence on the concentration x of K⁺ and reaches the lowest values at the MPB. The temperature dependences of the ferroelectric and dielectric properties at high temperatures may imply that the ceramics may contain both the polar and non-polar regions at temperatures above T _d.     

Ion-electron transfer in solid solutions Rb2 ? 2xFe2 ? xPxO4

The rubidium monoferrite RbFeO₂-based solid solutions with the composition Rb_{2 − 2x} Fe_{2 − x} P _x O₄ have been synthesized, and their crystal structure and the temperature and concentration dependences of the total and electron conductivities have been studied. The introduction of P⁵⁺ ions has been found to sharply decrease the electron conductivity that prevails in pure rubidium monoferrite and, at the same time, to increase the ionic conductivity. The latter becomes dominant as the phosphorus concentration increases. The maximum rubidium-cation conductivity of the materials under study is ∼3 × 10⁻² S/cm at 300°C and ∼3 × 10⁻¹ S/cm at 700°C. The results have been compared with the previously obtained data for similar solid solutions based on rubidium monogallate and monoaluminate.     

Electronic properties of LiMn2?xTixO4

Ti-substituted LiMn₂O₄ (LiMn_2−x Ti _x O₄, x=0, 0.15, 0.30, 0.45, 0.60, and 0.75) has been synthesized using solid-state reactions. Their crystal and electronic structures were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). XRD data suggested that the lattice parameters of LiMn_2−x Ti _x O₄ increase due to the replacement of Mn by Ti ions. XPS results indicated that the substituted Ti ions were in +4 oxidation state; consequently, the normal oxidation state of Mn ions has been detected by measuring the binding energy splitting of Mn 3s states, which decreases with the content of substituted Ti. The valence band spectra suggested that the intensity of e _g level of Mn 3d orbitals increased due to the increase of the Mn³⁺/Mn⁴⁺ ratio.     

Anomalous effect of magnetic field on the low-temperature thermal expansion of the Bi2Sr2?xLaxCuO6+δ and Nd2?xCexCuO4?δ HTSC systems in the non-superconducting phase

The thermal expansion of single crystals of the Bi₂Sr_2−x La _x CuO_6+δ high-temperature superconducting (HTSC) system in the insulating phase with compositions having no superconducting transition to a temperature of 1.8 K (x ≥ 0.8) is measured in an arbitrary direction in the (ab) plane in the temperature range of 7–50 K. Temperature regions of material compression upon heating are found. The study of anomalies in magnetic fields of 3 and 6 T, parallel and perpendicular to the c-axis revealed an anisotropic and nonmonotonic effect of the field on thermal expansion. Such anomalies for the n-type Nd_2−x Ce _x CuO_4−δ HTSC sample also having no superconducting transition are detected for the first time. The results show that the anomaly nature is caused by anisotropic electronic ordering, probably, by the charge density wave in the CuO₂ plane and superconductivity fluctuations in the insulating phase.     

Optical characterization in Pb(Zr1?xTix)1?yNbyO3 ferroelectric ceramic system

In this work, visible photoluminescence was observed at room temperature in a sintered Pb(Zr_1-xTi_x)_1-y Nb_yO₃\mathrm{Pb}(\mathrm{Zr}_{1-x}\mathrm{Ti}_{x})_{1-y} \mathrm{Nb}_{y}\mathrm{O}_{3} perovskite-type structure system, doped with Nb using the next excitation bands 325, 373 and 457 nm. The intensity and energy of such emissions have been studied by changing the Nb concentration (0<y<0.01) and the Ti content (x), with x=0.20,0.40,0.53,0.60 and 0.80, on both sides of the morphotropic phase boundary (MPB) zone. The principal bands become visible at energies of 1.73, 2.56 and 3.35 eV. The results reveal the role of the Nb⁵⁺ ion substitutions by Zr⁴⁺ or Ti⁴⁺ ions and the symmetry presented in the rhombohedral or tetragonal side of the MPB. Raman spectra which are similar for compositions: 20/80, 40/60 and 53/47 (tetragonal phases) show nine bands, centered around 137, 194, 269, 331, 434, 550, 612, 712 and 750 cm⁻¹. The spectra for samples 60/40 and 80/20, rhombohedral phase, show significant differences, only six bands appear, centered around 124, 209, 234, 330, 549 and 682 cm⁻¹. In addition, optical absorption spectroscopy, structural and micro-structural measurements were carried out by using Uv-vis spectroscopy, X-ray diffraction and scanning electron microscopy techniques, respectively. The experimental results of band gap energy, e.g., in our samples are in accordance with the findings by J. Baedi et al. in the calculations of band structure, energy gap and density of states for different phases of Pb(Zr_1−x Ti _x )O₃ using density functional theory (DFT).     

(1-x)(K0.5Na0.5)NbO3-xSrTiO3陶瓷的弛豫铁电性能

通过对（1-x）（K_0.5Na_0.5）NbO₃-xSrTiO₃（0≤x≤0.15）陶瓷的相组成、晶体结构和介电性能的研究发现,该陶瓷为单一的钙钛矿结构相.当x含量较小（x＜0.1）时为正交相结构,x≥0.1时转变为四方相结构.随着SrTiO₃掺杂量的增加,样品的致密度增加,样品由正常铁电相逐渐向弥散铁电相转变,且相 关键词： 弛豫铁电体 0.5Na_0.5）NbO₃铁电陶瓷')" href="#">（K_0.5Na_0.5）NbO₃铁电陶瓷 3掺杂')" href="#">SrTiO₃掺杂 相变温度     

Noncentrosymmetric cubic helical ferromagnets Mn1 ? yFeySi and Fe1 ? xCoxSi

Two systems of noncentrosymmetric cubic helical magnets Mn_{1 − y} Fe _y Si (y = 0.06, 0.08, 0.10) and Fe_{1 − x} Co _x Si (x = 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.50) have been compared. The concentration dependences of the critical temperature and magnetic field have been obtained using small-angle polarized-neutron scattering and analyzed in the framework of the Bak-Jensen model. It has been established that, among the two interactions that play the main role in these systems, i.e., the isotropic symmetric ferromagnetic exchange and the Dzyaloshinskii-Moriya isotropic antisymmetric interaction, the former interaction determines the critical temperature in the Mn_{1 − y} Fe _y Si system and the latter interaction determines this temperature in the Fe_{1 − x} Co _x Si system.     

Synthesis and characterization of ZnxHg1?xSeyS1?y quantum dots

This article describes the synthesis of highly water-soluble Zn _x Hg_1−x Se _y S_1−y quantum dots (QDs) in aqueous solution through a simple photo-assisted reaction between ZnSe QDs and mercury(I) nitrate dihydrate [Hg₂(NO₃)₂·2H₂O]. In order to deduce the optimal synthesis conditions, we varied several parameters, including the concentrations of mercaptosuccinic acid (MSA) and Hg₂(NO₃)₂·2H₂O, the illumination time, and the reaction temperature. When irradiated at temperatures below 80 °C, the ZnSe QDs reacted with the S²⁻ ions formed rapidly from MSA and the Hg²⁺ ions formed from Hg₂ ²⁺ ions to form Zn _x Hg_1−x Se _y S_1−y QDs through a process of photo-etching and surface combination. Under different conditions, we prepared a series of Zn _x Hg_1−x Se _y S_1−y QDs that emit fluorescence at the maximum wavelengths ranging from 405 to 760 nm. Inductively coupled plasma-mass spectrometry and transmission electron microscopy/energy dispersive spectrometry revealed that the content of Hg in the Zn _x Hg_1−x Se _y S_1−y QDs was greater when the synthesis was conducted at higher temperature. The Zn_0.88Hg_0.12Se_0.44S_0.56 QDs exhibit improved photostability than crude ZnSe QDs and possess long lifetimes (τ₁ ~ 38 ns and τ₂ ~ 158 ns).     

Effect of the spin and valence states of cobalt ions on the kinetic properties of Ho1 ? xSrxCoO3 ? δ and Er1 ? xSrxCoO3 ? δ compounds

The electrical conductivity and Seebeck effect in ceramics based on cobaltites Ho_{1 − x} Sr _x CoO_{3 − δ} (x = 0.65, 0.75, 0.85, 0.95) and Er_{1 − x} Sr _x CoO_{3 − δ} (x = 0.75, 0.85, 0.95) with a perovskite-like structure have been investigated in the temperature range T > 77 K. All the compounds under study are characterized by the variable-range-hopping conductivity with the temperature dependence of the electrical resistivity corresponding to the Mott law. It has been found that, in the Ho_0.35Sr_0.65CoO_{3 − δ} compound, thermally excited Co³⁺ ions contribute to the electrical conductivity with an increase in temperature to 250 K. The Seebeck coefficient of the systems studied decreases as the strontium concentration and temperature increase. It has been shown that, for an adequate explanation of this behavior, proper allowance must be made for the splitting of the 3d levels, as well as for the charge disproportionation of the cobalt ions.     

K0.5Bi0.5TiO3—Na0.5Bi0.5TiO3系统铁电陶瓷相界的X射线研究

用X射线衍射方法测定了K_0.5Bi_0.5TiO₃—Na_0.5Bi_0.5TiO₃系统不同组分试样的点阵常数和相变温度,确定了四方-三方相界组成。给出了K_0.5Bi_0.5TiO₃和Na_0.5Bi_0.5TiO₃的多晶X射线衍射数据。 关键词：     

Charge state of manganese ions and the nonstoichiometry of Ca1 ? xLayMnO3 ? δ single crystals

The charge states and effective spins of manganese ions in nonstoichiometric single crystals of Ca_{1 − x} La _y MnO_{3 − δ} (x = 0, 0.05, 1) manganites have been determined from the exchange splitting of Mn 3s X-ray photoelectron spectra. The chemical composition of the manganite samples under investigation, including the concentration of oxygen, has been determined using the data of the X-ray microanalysis of cations. It has been found that the manganite single crystals under investigation have large defectiveness in both the cation and oxygen sublattices. The efficiency of the complex use of 3s photoelectron spectroscopy and X-ray microanalysis in the determination of the charge state of manganese ions and violations of stoichiometry in doped and defected manganites has been demonstrated.