Synthesis and properties of solid solutions of hexagonal YCu0.5Ti0.5O3 with YMO3 (M = Mn, Cr, Fe, Al, Ga, and In)

Solid solutions of the type Y(Cu_0.5Ti_0.5)_1−xM_xO₃ with a hexagonal structure were prepared for M = Mn, Fe, Cr, Al, Ga, and In. A complete solid solution could be obtained only in the case of M = Mn. The green color of YCu_0.5Ti_0.5O₃ was found to be enhanced by small substitutions of Al, Ga, and In. All compositions containing Mn were black in color. Suppression of magnetic transitions is observed upon co-doping of Cu/Ti into YMnO₃. Measurements of dielectric constant suggest some magneto-electric coupling may be present in the Y(Cu_0.5Ti_0.5)_1−xMn_xO₃ solid solution.     

Synthesis under high-oxygen pressure, magnetic and structural characterization from neutron powder diffraction data of YGa1−xMn1+xO5 (x = 0.23): A comparison with YMn2O5

A new material of nominal stoichiometry YGaMnO₅ has been prepared in polycrystalline form from citrate precursors followed by thermal treatments under high-oxygen pressure. This compound has been characterized from neutron powder diffraction (NPD) data and magnetic measurements. For comparison, the parent compound YMn₂O₅ has also been synthesized and its crystal structure refined by NPD data. The new oxide has an actual stoichiometry YGa_1−xMn_1+xO₅ (x = 0.23), determined by NPD, showing an important cationic disorder between both metal sites; it is orthorhombic, Pbam (SG), and its crystal structure contains chains of Mn⁴⁺O₆ edge-sharing octahedra, linked together by Ga³⁺O₅ pyramids and YO₈ units. With respect to YMn₂O₅, containing axially elongated MnO₅ pyramids due to the Jahn-Teller effect of Mn³⁺ cations, the GaO₅ pyramidal units in YGa_0.77Mn_1.23O₅ are substantially flattened. This compound has a paramagnetic behaviour with two weak anomalies at about 50 K and 350 K. The magnetic structures, studied at 1.4 K and 100 K show a ferromagnetic coupling along the chains of MnO₆ octahedra.     

X-ray, IR and bulk magnetic properties of Cu1 + x Mn x Fe2–2x O4 ferrite system

The structural, IR and magnetic properties of the mixed spinel Cu_{1 + x} Mn _x Fe_2-2x O₄ (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) system have been investigated by means of X-ray diffraction, Infrared spectroscopy, magnetization and a.c. susceptibility measurements. X-ray results confirm single-phase spinel structure for all the concentrations. The structure of CuFe₂O₄ is tetragonal and changes to cubic for x = 0.1 to 0.4. For x = 0.5 and 0.6 the structure become tetragonal. The lattice parameter and X-ray density are deduced and their variation with Mn⁴⁺ concentration is studied. The cation distribution derived from the X-ray diffractometry data was found to agree very well with the cation distribution obtained from magnetization measurements. X-ray intensity calculations indicate that Mn⁴⁺ occupy only octahedral [B] sites and Cu²⁺ and Fe³⁺ ions occupy both octahedral [B] and tetrahedral (A) sites. The infrared spectra obtained at room temperature in the range 200–800 cm^–1 showed two absorption bands. The force constants have been obtained from IR data. The variation of the saturation magnetization per formula unit as a function of Mn⁴⁺ content x has been satisfactorily explained on the basis of Neel's collinear spin ordering model for all values of x. The Curie temperature T _C determined from a.c. susceptibility data decreases with increase of Mn⁴⁺ concentration x, suggesting decrease in ferrimagnetic behaviour.     

Effect of Zn<Superscript>2+</Superscript> doping on the structural,magnetic and dielectric properties of MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by the sol–gel method

Mn_1?xZn_xFe₂O₄ (x?=?0.2–0.8) ferrite samples were successfully prepared by the sol–gel method. X-ray diffraction study reveals that single cubic spinel phase was formed in Mn_1?xZn_xFe₂O₄ samples. The SEM micrographs revealed that the microstructures change significantly with different Zn²⁺ doping concentration and sintering temperature while the grain size grow up to 9.48 μm for Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C. Further, the dielectric and magnetic measurements indicated that both Zn²⁺ doping and sintering temperature could affect both electrical and magnetic parameters such as dielectric constant and saturation magnetization in a great manner. The Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C for 8 h is found to show the largest M _s value (77.30 emu/g) in this work. These results indicate that Zn²⁺ doping or sintering temperature can adjust the microstructures, dielectric and magnetic properties of Mn_1?xZn_xFe₂O₄ ferrites.     

R3Mn1.5CuV0.5O9 (R = Y, Ho, Er, Tm, Yb and Lu) and Lu3Mn3−3xCu2xVxO9: New noncentrosymmetric oxides related to YMnO3

We report formation of new noncentrosymmetric oxides of the formula, R₃Mn_1.5CuV_0.5O₉ for R = Y, Ho, Er, Tm, Yb and Lu, possessing the hexagonal RMnO₃ (space group P6₃cm) structure. These oxides could be regarded as the x = 0.5 members of a general series R₃Mn_3−3xCu_2xV_xO₉. Investigation of the Lu-Mn-Cu-V-O system reveals the existence of isostructural solid solution series, Lu₃Mn_3−3xCu_2xV_xO₉ for 0 < x ≤ 0.75. Magnetic and dielectric properties of the oxides are consistent with a random distribution of Mn³⁺, Cu²⁺ and V⁵⁺ atoms that preserve the noncentrosymmetric RMnO₃ structure.     

The investigation of Zn content on the structure and electrical properties of Zn x Cu0.2Ni0.66Mn2.14?x O4 negative temperature coefficient ceramics

The effects of Zn content on the structure and electrical properties of Cu–Ni–Mn–O based negative temperature coefficient thermistors were investigated. Series of Zn _x Cu_0.2Ni_0.66Mn_2.14?x O₄ (0?≤?x?≤?1) ceramics were prepared by Pechini method. Cu2p_3/2 X-ray photoelectron spectra demonstrate that Cu⁺ and Cu²⁺ ions at A sites decrease with increase of x, and all the Cu ions exist as Cu²⁺ (B) at x of 1.0 due to the almost exclusive occupation of Zn ions at A sites. X-Ray diffraction spectra show that a single cubic spinel structure is formed at a low Zn content (x?≤?0.6), and NiO and CuO start to appear at x of 0.8. The segregation of NiO at x?≥?0.8 is caused by the migration of Cu ions for A to B sites. With Zn content x increasing from 0 to 1.0, the electrical resistivity increases from 42 to 980?Ω?cm which can be attributed to the decrease of the electrical conduction caused by Cu ions at A sites. The resistivity drift decreases sharply from 12.6 to 4.2% with increasing x from 0 to 0.4, and the value is only 0.16% at x of 1.0.     

Structural aspects of adamantine like multinary chalcogenides

The present state of knowledge of structure, phase relations and metal ordering in 2(ZnX)_x(CuBX₂)_1 − x (B = Ga, In and X = S, Se, Te) and Cu₂Zn_xFe_1 − xSnS₄ multinary compounds is discussed. The chemical disorder process in 2(ZnX)_x(CuBX₂)_1 − x alloys leads to a phase separation, i.e. in a certain composition range (2-phase field) two phases, tetragonal domains and a cubic matrix, coexist. Its width depends on the three-valent cation only and is independent from the size of anion. In the subsolidus region of the 2(ZnX)_x(CuBX₂)_1 − x system the stability range of tetragonal mixed crystals as well as the miscibility gap is decreasing, the stability range of cubic mixed crystals is increasing. The process of structural disorder in 2(ZnX)_x(CuBX₂)_1 − x as well as Cu₂Fe_1 − xZn_xSnS₄ alloys is connected to the cation substructure. In tetragonal 2(ZnX)_x(CuInX₂)_1 − x alloys a non-random Zn distribution on the both cation positions of the chalcopyrite-type structure was revealed, whereas a random distribution of Zn and Cu on two different sites of the kesterite type structure was obtained in Cu₂ZnSnS₄ in contradiction to literature. The crossover from stannite (x = 0) to kesterite (x = 1) in Cu₂Fe_1 − xZn_xSnS₄ is considered as a three-stage process of cation restructure involving Cu⁺, Zn²⁺ and Fe²⁺, whereas Sn⁴⁺ does not take part in this process. In tetragonal 2(ZnX)_x(CuInX₂)_1 − x alloys the anion displacement is decreasing with increasing ZnX content in CuInX₂ indicating a decreasing tetragonal distortion. Here the disorder process in the cation substructure and the displacement process in the anion substructure are coupled.     

Multifunctional Zn0.99−xMn0.01CuxS nanowires: Structure, luminescence and magnetism

The wurtzite-type Zn_0.99−xMn_0.01Cu_xS (x = 0, 0.003, 0.01) nanowires were prepared by a simple hydrothermal method at 180 °C. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron micrograph (FESEM) and X-ray photoelectron spectrum (XPS). The results showed that both the Mn²⁺ and Cu²⁺ ions substituted for the Zn²⁺ sites in the host ZnS. The ethylenediamine-mediated template was observed, which was used to explain the growth mechanism of the nanowires. The color-tunable emission can be obtained by adjusting the concentrations of Mn²⁺ and Cu²⁺ ions. The ferromagnetism was observed around room temperature.     

Effect of nonstoichiometry on the structure and microwave dielectric properties of Ba1 ? x(Zn1/2W1/2)O3 ? x and Ba(Zn1/2 ? yW1/2)O3 ? y/2

We have synthesized Ba_{1 − x} (Zn_1/2W_1/2)O_{3 − x} and Ba(Zn_{1/2 − y} W_1/2)O_{3 − y/2} barium tungstates with different deviations from cation stoichiometry (x = 0.01–0.05, y = 0.01–0.05), determined the phase composition of ceramics fabricated from the tungstates, and investigated their electrical properties. Even slight deviations from cation stoichiometry in Ba(Zn_1/2W_1/2)O₃ lead to the formation of the scheelite phase BaWO₄, and its content increases with heat-treatment temperature. Barium or zinc deficiency in the systems studied improves the sintering behavior of Ba(Zn_1/2W_1/2)O₃ and increases the degree of 1: 1 B-site cation ordering, which in turn ensures an increase in microwave quality factor, Q.     

Weak ferromagnetic polar phase in the BiFe1−xTixO3 multiferroics

Neutron powder diffraction and magnetization measurements of selected samples of the BiFe_1?xTi_xO₃ series were performed. Ti⁴⁺ substitution was shown to induce the appearance of weak ferromagnetism in the initial polar R3c phase stable at x ≤ 0.1. In the concentration range 0 ≤ x ≤ 0.1, room-temperature residual magnetization increases from 0 to 0.25 emu/g (the latter is characteristic of the field-induced weak ferromagnetic state in pure BiFeO₃). The calculated ferroelectric polarization decreases from ~70 μC/cm² (x = 0) to ~60 μC/cm² (x = 0.1) at room temperature. Magnetic ordering coexists with the large spontaneous polarization in a broad temperature range to make the BiFe_1?xTi_xO₃ (x → 0.1) perovskites promising for multiferroic applications.     

Structural, Magnetic and Electrical Properties of Cu Substituted Mn–Zn Soft Nanoferrites

Soft nanoferrites of nominal composition Mn_0.5Cu _x Zn_0.5?x Fe₂O₄ with 0.0??x??0.35 were prepared by chemical co-precipitation method. The formation of single phase spinel structure with different compositions, sizes and macrostructure were confirmed by X-ray diffraction patterns and scanning electron microscopic (SEM) measurements. The lattice parameter decreased with increase in Cu²⁺ content. The crystallite size of the powder samples varied from?14 to 27?nm. The theoretical density increased with increase in Cu²⁺ content. Room temperature saturation magnetization was measured as a function of copper content. The saturation magnetization (Ms) and Bohr magneton (?? _B) increases up to x=0.25 due to increased A?CB interactions in the AB₂O₄ type spinel nanoferrites. Dielectric permittivity, dielectric loss tangent and complex impedance plots were studied in the frequency range 20?Hz?C5?MHz. Loss peak occurs for all the studied compositions and shifts towards low frequency with increased Cu²⁺ content. Complex impedance spectroscopic studies confirmed that conduction in the samples is due to grain boundaries. The high values of DC electrical resistivity support this result.     

Ultrasonic, Transport, and Magnetic Properties of Nd0.5Sr0.5Mn1−x Cr x O3 Perovskites

The resistivity, magnetization and longitudinal ultrasonic velocity (V _l) have been measured in single-phase polycrystalline Nd_0.5Sr_0.5Mn_1?x Cr _x O₃ (x=0, 0.02, 0.05, 0.1) to clarify the Cr doping effect on the metal-insulator and charge ordering transitions. For x=0 sample, the V _l shows two large stiffening just below the metal-insulator transition temperature T _MI and the charge ordering temperature T _CO, respectively. It is suggested that the former ultrasonic anomaly may originate from the spin-lattice effect and the dynamic Jahn-Teller effect, and the latter is due to the electron-lattice effect arising from the static Jahn-Teller effect of Mn³⁺. With the Cr doping, the T _MI shifts to lower temperature, the maximum of magnetization becomes smaller and the resistivity remains metallic type. Furthermore, only one stiffening of ultrasonic velocity is observed below T _MI in these doping samples. The analysis suggests that the Cr doping enhances the double exchange between Mn³⁺ and Mn⁴⁺, and thoroughly destroys the charge ordering state.     

On the stability of the cubic spinel structure in the system CuMnO

The stability range of the cubic spinel structure in the Cu_xMn_3?xO₄-system is determined with x-ray diffraction on quenched specimens. At room temperature metastable cubic spinels can be obtained for the composition range 1.06 <- x <- 1.50. It is shown that stoichiometric cubic CuMn₂O₄ cannot be obtained as a single phase at room temperature because of the intrinsic Mn³⁺ clustering, which results in a segregation of γ-Mn₂O₃ near 300°C, and which in turn transforms very quickly into α-Mn₂O₃. The ionic order in Cu_1.5Mn_1.5O₄ is indicative that tetrahedral Cu⁺ ions are stable in presence of octahedral Cu²⁺ and Mn⁴⁺ ions.     

Homogeneity Range of Samarium Manganite in Air

The solubility limits of samarium and manganese oxides in SmMnO₃ are determined using x-ray diffraction analysis of Sm_{2 ? x}MnxO₃ samples (0.90 ≤ x ≤ 1.20, Δx = 0.02) prepared from oxide mixtures by solid-state reactions in air between 800 and 1400°C. The composition dependences of lattice parameters are presented for samarium manganite synthesized at 1400°C. The solubility of samarium oxide in SmMnO₃ is tentatively attributed to structural defects, and that of manganese oxides is interpreted in terms of structural defects, oxygen nonstoichiometry of samarium manganite, the disproportionation reaction 2Mn³⁺ =Mn²⁺ + Mn⁴⁺, and partial substitution of the resulting Mn₂₊ for Sm₃₊ on the cuboctahedral site of the perovskite structure.     

Unusual e g 3d x 2−y 2 Orbital Ordering and Low-Energy Excitations in the CE Structure of NaMn7O12

Similarly to the half-doped manganese oxides with perovskite structure like La_0.5Ca_0.5MnO₃, the double perovskite compound NaMn₇O₁₂ contains an equal number of Mn³⁺ and Mn⁴⁺ ions in the corner-sharing network of MnO₆ octahedra and exhibits a CE order of the charge and spins of these ions at low temperature. Though, in NaMn₇O₁₂ the order is complete, the charge and spin ordering transitions are sharp and the system is free of disorder, phase coexistence or structural inhomogeneities thanks to the absence of chemical substitutions. Here we discuss two unusual features of the CE structure of NaMn₇O₁₂: (1) the e _g 3d x ²?y ² orbital ordering expected from the direct crystallographic observation of compressed Mn³⁺O₆ octahedra below the charge ordering transition; (2) the existence of a large amount of low-energy excitations evidenced by the low temperature behavior of the specific heat. We propose a picture of nearly degenerate spin and orbital configurations of the CE structure arising from the peculiar orbital ordering.     

Dispersion of dielectric constant and resistivity of Cu x Zn1−x Fe2O4 samples

Cu _x Zn_1−x Fe₂O₄ samples exhibit dispersion of dielectric constant, tanδ and resistivity in the frequency range of 1 kHz to 50 MHz. The dispersion exhibited is in general accord with Koops’ model. However, the details of the conducting and non-conducting regions must be taken into account when composition tends to change interrelationship between the elementary capacitor resistor circuits. On quenching these samples from 800°C the dielectric constantε ¹ showed an increase for CuFe₂O₄ and Cu_0·8Zn_0·2Fe₂O₄ samples. The dielectric constant of the remaining samples showed no influence on quenching. The compositional variation showed that the dielectric constant has higher value for the ferrite Cu_0·4Zn_0·6Fe₂O₄ The results are explained on the basis of cation transfer.     

Cation Distribution in the CuxMn3 – xO4 and CuMxMn2 – xO4 (M = Cr, Al) Spinels

The Rietveld profile analysis method applied to x-ray diffraction data was used to assess the cation distribution in the Cu _x Mn_{3 – x} O₄ (x = 0.5, 0.75, 1.00) solid solutions at 900°C in air and after quenching and also in quenched CuCr _x Mn_{2 – x} O₄ and CuAl _x Mn_{2 – x} O₄ (0 x 2.0) solid solutions. The results show that the tetragonal distortion (c/a 1) of the spinel structure depends on the relative occupancies of the Jahn–Teller ions Cu²⁺ and Mn³⁺ on the octahedral and tetrahedral sites and also on whether the system is in an equilibrium or metastable state. The structure of the solid solutions may also be affected by clusterization of octahedral Jahn–Teller ions. The resultant contents of Jahn–Teller ions leading to one or the other type of tetragonal distortion are evaluated.     

Regular Arrays of (Zn,Mn)S Quantum Wires with Well-Defined Diameters in the Nanometer Range

Zn_1–x Mn _x S, with x varying between 0.01 and 0.30, were formed inside the ordered pore systems of different mesoporous SiO₂ matrices. Because of the highly ordered structure of the hosts, regular arrays of Zn_1–x Mn _x S quantum wires with lateral dimensions of 3 and 5.5 nm, respectively, separated by 2-nm SiO₂ barriers were obtained. The wires were characterized using photoluminescence (PL) and PL excitation (PLE) spectroscopy at liquid Helium temperatures. The PL of the wires is dominated by the ⁴T₁ ⁶A₁ internal transition of the Mn²⁺(3d⁵) ions. The corresponding PLE spectra show higher internal Mn transitions as well as the band to band transition. The energies of the internal Mn transitions are typical for Mn²⁺ on a cation site of (II,Mn)VI semiconductors. Because of the comparable bandgaps of the SiO₂ and the Zn_1–x Mn_xS as well as the small exciton Bohr radius in (Zn,Mn)S quantum confinement effects in the wires are less than about 150 meV.     

Structural and electrical properties of fritless Ni(1?x)CuxMn2O4 (0?≤?x?≤?1) thick film NTC ceramic

Spinel structured NTC thermistor Ni_(1−x)Cu _x Mn₂O₄ (0 ≤ x ≤ 1) ceramics was prepared by oxalic precursor method and fritless thick films screen printed on alumina. The composition dependent structural and electrical properties are reported in this paper. The results show that with increasing copper ion substitution both Cu²⁺ and Mn⁴⁺ predominantly occupy the octahedral site. The concentration of Cu²⁺ ions in octahedral site increases while that of Ni²⁺ ions decreases linearly. The thick film Ni_(1−x)Cu _x Mn₂O₄ ceramic comply with Arrhenius equation. A thermistor constant of ~1,200 K has been obtained for fritless thick film NTC ceramics using inorganic binders in the RT/90 thermal range.     

Stability region of Eu<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>x</Subscript>O<Subscript>3+δ</Subscript> solid solutions in air

The homogeneity range of EuMnO₃ has been determined using x-ray diffraction analysis of single-and mixed-phase Eu_2?x Mn_xO_3+δ samples (0.90≤x≤1.20, Δx = 0.02) prepared from oxide mixtures by solid-state reactions in air between 900 and 1400°C. The results have been used to construct a partial phase diagram of the Eu-Mn-O system in air. The dependences of unit-cell parameters on x and synthesis temperature are presented for the samples synthesized at 1100 and 1400°C and for EuMnO₃, respectively. The solubility of europium oxide in EuMnO₃ is tentatively attributed to structural defects, and that of managanese oxides is interpreted in terms of structural defects, oxygen nonstoichiometry of europium manganite, the disproportionation reaction 2Mn³⁺ = Mn²⁺ + Mn⁴⁺, and partial substitution of the resulting Mn²⁺ for Eu³⁺ on the cuboctahedral site of the perovskite-like structure. To check these assumptions, systematic studies of the oxygen nonstoichiometry and structure of Eu_2?x Mn_xO_3+δ solid solutions synthesized at different temperatures are needed.