Effect of thermo-mechanical histories on the microstructure and properties of Zr<Subscript>65</Subscript>Al<Subscript>10</Subscript>Ni<Subscript>10</Subscript>Cu<Subscript>15</Subscript> metallic glassy plates

Effect of thermo-mechanical histories during hot rolling in the supercooled liquid region on the microstructure and properties of Zr₆₅Al₁₀Ni₁₀Cu₁₅ metallic glassy plates was investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), differential scanning calorimetry (DSC), microhardness and electrical resistivity measurements. It was found that some nano-scale clusters and a few crystalline phases were dispersed in the amorphous matrix, which may depress the crystallization onset temperature (T_x). The microhardness increased while the electrical resistivity first increased and then decreased with hot rolling times. So, it is important for the working and forming of bulk metallic glasses in the supercooled liquid region to take the thermo-mechanical histories into account.     

Relaxor behavior and ferroelectric properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-K<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-KNbO<Subscript>3</Subscript> lead-free ceramics

Lead-free ferroelectric ceramics of (1−x) [0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃]-x KNbO₃(x = 0, 0.02, 0.04, and 0.06) were prepared by the conventional ceramic fabrication technique. The crystal structure, dielectric properties and P-E hysteresis loops were investigated. XRD data showed that all compositions could form pure perovskite structure. Temperature dependence of dielectric constant ε _r and dissipation factor tanδ measurement between room temperature and 500^∘C revealed that the compounds experience phase transitions that from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric in the range of x = 0–0.04. The frequency dependent dielectric constant showed these compounds were relaxor ferroelectric. At low frequency and high temperature, dielectric constant and dissipation factor increased sharply attributed to the superparaelectric clusters after the KNbO₃ doped.     

Enhancement in electrical conductivity of Li<Subscript>2</Subscript>O: B<Subscript>2</Subscript>O<Subscript>3</Subscript>: V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The study of electrical conductivity of 30Li₂O: (70 − x) B₂O₃: xV₂O₅ glass samples has been carried out. The results have been explained by dividing the temperature range into two regions. In region I, conductivity shows Arrhenius behaviour for all the samples. The conductivity increases with addition of V₂O₅. The results have been explained in the light of Anderson and Stuart Model. In region II, an anomalous enhancement in the conductivity is observed for all the samples up to certain temperature beyond which the conductivity decreases. The enhancement in the conductivity in the annealed glass sample has been attributed to nanocrystallization.     

Synthesis of Ba<Subscript>3</Subscript>ZnNb<Subscript>2</Subscript>O<Subscript>9</Subscript>−Sr<Subscript>3</Subscript>ZnNb<Subscript>2</Subscript>O<Subscript>9</Subscript> solid solution and their dielectric properties

Oxides of the type, Ba_3-xSr_xZnNb₂O₉ (0 ≤x ≤3), were synthesized by the solid state route. Oxides calcined at 1000°C show single cubic phase for all the compositions. The cubic lattice parameter (a) decreases with increase in Sr concentration from 4.0938(2) forx = 0 to 4.0067(2) forx = 3. Scanning electron micrographs show maximum grain size for thex = 1 composition (∼ 2 μm) at 1200°C. Disks sintered at 1200°C show dielectric constant variation between 28 and 40 (at 500 kHz) for different values of x with the maximum dielectric constant atx = 1.     

Low-field Magnetoresistance,Specific Heat and Magnetocaloric Effect in Sr Substituted Pr<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>

We investigate the effect of ionic size variation on the electrical and thermodynamic properties in a series of Pr_0.7Ca_0.3−x Sr _x MnO₃ (PCSMO) samples. The increase in Sr content results in an increase of the unit cell volume, as a bigger Sr²⁺ ion replaces the smaller Ca²⁺ ions. Resistivity measurements show that the increase in the Sr content also results in the induction of a metal–insulator transition (T _MI), which increases with increasing Sr content. The activation energy (E _a), calculated from the resistivity data, decreases with increasing Sr content confirming the metallic character. The effect of the magnetic field on resistivity and specific heat has also been studied.     

Superprotonic CsH<Subscript>2</Subscript>PO<Subscript>4</Subscript>-CsHSO<Subscript>4</Subscript> solid solutions

We have performed partial HSO₄⁻ substitution in CsH₂PO₄ and studied the associated structural changes and the proton conductivity of the resultant (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions in the range x = 0.01–0.3. The results indicate that, at room temperature, the solid solutions are disordered. In the range x = 0.01–0.1, they are isostructural with the low-temperature phase of CsH₂PO₄ (sp. gr. P2₁/m), and their unit-cell parameters increase with x, whereas in the range x = 0.15–0.3 the solid solutions are isostructural with the high-temperature, cubic phase of CsH₂PO₄ (Pm3m), and their unit-cell parameter decreases. The conductivity of the (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions with x ≤ 0.3 depends significantly on their composition and increases at low temperatures by up to four orders of magnitude, approaching that of the superionic phase of CsH₂PO₄ in the range x = 0.15–0.3 because of the hydrogen bond weakening and increased proton mobility. The conductivity of the superionic phase decreases with increasing x by no more than a factor of 1.5–2, and the superionic phase transition, which occurs at 231°C in CsH₂PO₄, shifts to lower temperatures and disappears for x ≥ 0.15. The activation energy for low-temperature conduction decreases with increasing x: from 0.9 eV in CsH₂PO₄ to 0.48 eV at x = 0.1.     

Study of structure and properties of ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the ternary system ZnO–Bi₂O₃–P₂O₅ were prepared and studied in two compositional series 50ZnO–xBi₂O₃–(50 − x)P₂O₅ and (50 − y)ZnO–yBi₂O₃–50P₂O₅. Two distinct glass-forming regions were found in the 50ZnO–xBi₂O₃–(50 − x)P₂O₅ glass series with x = 0–10 and 20–35 mol.% Bi₂O₃. All prepared Bi₂O₃-containing glasses reveal a high chemical durability. Small additions of Bi₂O₃ (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C. Structural studies by Raman and ³¹P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q⁰ phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO₆ units and their vibrational bands were observed within the spectral region of 350–700 cm⁻¹. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi₂O₃.     

Phase transition and electrical properties of LiNbO<Subscript>3</Subscript>-modified K<Subscript>0.49</Subscript>Na<Subscript>0.51</Subscript>NbO<Subscript>3</Subscript> lead-free piezoceramics

Lead-free (1-x)K_0.49Na_0.51NbO₃-xLiNbO₃ (KNN-LN, x = 0 ~ 0.08) piezoelectric ceramics were prepared by the conventional solid-state sintering method. The effects of LiNbO₃ doping amount x on the phase transition behavior and the electrical properties of KNN-LN ceramics were investigated. By increasing LiNbO₃ doping amount x, the orthorhombic-tetragonal polymorphic phase transition (PPT) temperature (T _o–t) of KNN-LN ceramics shifted downwards, however, the Curie temperature (T _c) slightly moved upwards. The room temperature phase structure thus changed from orthorhombic to tetragonal across the compositions with 0.05 ≤ x ≤ 0.06, named as PPT region. The composition with x = 0.06 in the tetragonal side of PPT region exhibited optimized electrical properties of d ₃₃ = 246pC/N, k _p = 41.6%, ε _r = 679, tgδ = 0.028, and Q _m = 52. In addition to its very high T _c = 467 °C, this ceramic can be an excellent candidate for replacing the lead-based piezoceramics in high temperature applications.     

Sol–gel synthesis of Ce-substituted BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>

Ce-substituted BaFe₁₂O₁₉ (BaCe _x Fe_12−x O₁₉, x = 0, 0.01, 0.03, 0.05) was prepared by citrate sol–gel method. The thermal decomposition process of precursor was investigated by TG-DSC. The phase composition of the BaCe _x Fe_12−x O₁₉ was characterized by X-ray powder diffraction analysis (XRD) which reveals that the BaCe _x Fe_12−x O₁₉ crystallizes in a hexagonal structure. The lattice parameter of BaCe _x Fe_12−x O₁₉ increases slightly when Ce was substituted into BaFe₁₂O₁₉. The average crystallite size calculated from the XRD line broadening is about 30–33 nm and no intermediate phases are detected in the XRD patterns. The transmission electron microscope (TEM) analysis indicates that the particles of samples obtained are the rod-like morphology.     

Crystallization kinetic studies of CaBi<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>7</Subscript> glasses by non-isothermal methods

Transparent glasses of CaBi₂B₂O₇ (CBBO) were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were, respectively, confirmed by X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC). The glass transition (T _g) and the crystallization parameters (crystallization activation energy (E _cr) and Avrami exponent (n)) were evaluated under non-isothermal conditions using DSC. The heating rate dependent glass transition and the crystallization temperatures were rationalized by Lasocka equation for the as-quenched CBBO glasses. There was a close agreement between the activation energies for the crystallization process determined by Augis and Bennet and Kissinger methods. The variation of local activation energy (E _c(x)) that was determined by Ozawa method increased with the fraction of crystallization (x). The Avrami exponent (n(x)) decreased with the increase in fraction of crystallization (x), suggesting that there was a changeover in the crystallization process from the bulk to the surface.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

Formation of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + <Emphasis Type="Italic">x</Emphasis></Subscript> clusters in laser-generated plasma

We have studied the influence of YBa₂Cu₃O_{6 + x} clusters formed in the plasma generated by laser ablation of a YBa₂Cu₃O_{7 ? δ} target on the optical transmission spectra of amorphous YBaCuO films deposited on glass substrates arranged along the direction of predominant plasma expansion in the laser plume. It is established that intense cluster formation begins in the region of rapid decrease in the film thickness, where the temperature of plasma decreases to a level at which stable atomic complexes characteristic of the target composition can form (under the experimental conditions studied, this was observed at as distance of L > 6 cm from the target). As the amount of clusters in the deposit increases, the magnitude of the interference fringes, which are characteristic of optically homogeneous media, gradually decreases and eventually almost vanishes. At the same time, features typical of the electron structure of YBa₂Cu₃O_{7 ? δ} appear and grow in the optical transmission spectra of the YBaCuO films, including the absorption due to free charge carriers at ?ω < 1.2 eV (characteristic of “metallic” clusters) and the minima at ?ω = 1.4 and 1.75 eV (characteristic of a dielectric state).     

Er-Doped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

LiMn_2-x Er_xO₄ (x ≤ 0.02) materials were synthesized by a rheological phase reaction method. The thermal behavior of the materials was examined by thermogravimetric and differential scanning calorimetry. X-ray diffraction showed that the samples (x ≤ 0.02 ) exhibited the same phase as the pure spinel. The lattice parameter of the Er-doped spinel was smaller than that of the undoped one and decreased with increasing doping level. Cyclic voltammograms showed two reversible processes corresponding to the typical response of spinel LiMn₂O₄ and revealed an insertion-extraction reaction occurring at two stages in the 4-V region. The electrochemical performances of the samples were studied and displayed a better reversibility and cyclability.__________From Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 740–743.Original English Text Copyright © 2005 by Haowen Liu, Li Song, Kelli Zhang.This article was submitted by the authors in English.     

Scaling of the Temperature Dependent Resistivity and Hall Effect in Ba(Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)As<Subscript>2</Subscript>

We show that the temperature-dependent resistivity ρ(T), Hall number n _H(T) and the cotangent of the Hall angle cot θ _H(T) of Ba(Fe_1−x Co _x )As₂ (x=0.0–0.2) can be scaled using a recently proposed model-independent scaling method (Luo et al. in Phys. Rev. B 77:014529, 2008). The zero field normal-state resistivity above T _c can be reproduced by the expresion r(T) = r₀ +cTexp(- \frac2\varDelta T )\rho(T) = \rho_{0} +cT\exp(- \frac{2\varDelta }{T} ) and scaled using the energy scale Δ, c and the residual resistivity ρ ₀ as scaling parameters. The scaling parameters have been calculated and the compositional variation of 2Δ and ρ ₀ has been determined. The 2Δ(x) dependence show almost linear decreasing in underdoped regime, minimum corresponding to the T _c maximum and increasing in overdoped regime. The latter is different from that reported for cuprates. The existence of a universal metallic ρ(T) curve which, however, is restricted for the underdoped compounds to temperatures above a structural and antiferromagnetic transition is interpreted as an indication of a single mechanism which dominates the scattering of the charge carriers in Ba(Fe_1−x Co _x )As₂ (x=0.0–0.2).     

Inhomogeneous State of the Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Doped with Manganese

Basing on electron spin resonance (ESR) data for Bi₂Te₃ doped by Mn ions we argue that this compound can be inhomogeneous and consists of two components with the different structures. Its main phase Bi _2?x Mn _x Te ₃ is intertwined with the microscopical inclusions of MnBi phase. The integral volume of these intermetal clusters is less than 1 % but nevertheless they exert the serious impact on the dynamic magnetic properties of the entire system. These inclusions are ferromagnetic with the Curie temperature of 630 K, while the main bulk phase Bi _2?x Mn _x Te ₃ has x= 0.05 orders at T _c= 10 K (qualitatively this twophase picture is valid not only for this given x). Below this temperature two ferromagnetic phases coexist. Since the integral spontaneous polarization in MnBi phase is averaged out due to its random orientations in different clusters the time-reversal symmetry of Bi ₂Te ₃ doped by Mn ions is violated only at the low-temperature ferromagnetic transition.     

Photoluminescence and Electrical Conductivity of As<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Au〉 and As<Subscript>2</Subscript>S<Subscript>5</Subscript>〈Au〉 Glasses

The 77-K photoluminescence spectra of (As₂S₃)_{100 − x} Au_x and (As₂S₅)_{100 −x} Au_x (0 ≤ x ≤ 0.04) semiconducting glasses are measured for the first time. At low doping levels, the spectra of the (As₂S₅)_{100 − x} Au_x glasses are split into two components, one of which arises from the Au dopant. The temperature-dependent conductivity of the glasses shows two breaks at low Au concentrations and anomalous behavior in the range 300–360 K. Qualitative analysis of the conductivity data suggests that most of the impurity atoms have saturated valence bonds and form solid solutions with host atoms, changing the band gap of the material. A small fraction of the impurity atoms, those having unsaturated valence bonds, produce an electrically active level responsible for impurity conduction.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 876–880.Original Russian Text Copyright © 2005 by Babaev, Kamilov, Sultanov, Askhabov, Terukov.     

Peculiarities of the electric conductivity of As<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Au〉 and As<Subscript>2</Subscript>S<Subscript>5</Subscript>〈Au〉 glasses

The temperature dependences of the dc conductivity in glasses of the (As₂S₃)_1−x Au_x and (As₂S₅)_1−x Au_x systems (0.04 at. % ≥x≥0) are reported for the first time. The curves show an anomalous behavior in the temperature interval of 360 K<T<300 K and exhibit a break for glass compositions with a low gold content. A model explaining the existence of impurity conductivity is proposed.     

Defects in Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te-based heterostructures grown by molecular beam epitaxy on GaAs(310) substrates

Cd _x Hg_{1 − x} Te-based epitaxial heterostructures grown on [310]-oriented GaAs substrates by molecular beam epitaxy have been studied by atomic force, scanning electron, and high-resolution field emission microscopy. A mechanism of defect formation has been proposed. The microstructure of the epilayer has been investigated in greatest detail. We have analyzed the key features of V-defect formation, in particular using depth profiling of the heterostructures by ion etching. A comparative analysis of the elemental compositions of V-defects and a defect-free region has been performed. The results indicate that, in the central part of the V-defects, the excess tellurium content is ∼2.5% and mercury deficiency is ∼3%. V-defect formation in the heterostructures is related to tellurium precipitation, which initiates nucleation of polycrystalline clusters and dislocation generation in adjacent regions.     

Electrical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript>-CaO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses exhibiting majority charge carrier reversal

The thermoelectric power and d.c electrical conductivity of x V₂O₅⋅40CaO⋅(60−x)P₂O₅ (10 ≤ x ≤ 30) glasses were measured. The Seebeck coefficient (Q) varied from +88 μ V K⁻¹ to −93 μV K⁻¹ as a function of V₂O₅ mol%. Glasses with 10 and 15 mol% V₂O₅ exhibited p-type conduction and glasses with 25 and 30 mol% V₂O₅ exhibited n-type conduction. The majority charge carrier reversal occurred at x = 20 mol% V₂O₅. The variation of Q was interpreted in terms of the variation in vanadium ion ratio (V^{5 +}/V^{4 +}). d.c electrical conduction in x V₂O₅⋅40CaO⋅(60−x)P₂O₅ (10 ≤ x ≤ 30) glasses was studied in the temperature range of 150 to 480 K. All the glass compositions exhibited a cross over from small polaron hopping (SPH) to variable range hopping (VRH) conduction mechanism. Mott parameter analysis of the low temperature data gave values for the density of states at Fermi level N (E_F) between 1.7 × 10²⁶ and 3.9 × 10²⁶ m⁻³ eV⁻¹ at 230 K and hopping distance for VRH (R_VRH) between 3.8 × 10⁻⁹m to 3.4 × 10⁻⁹ m. The disorder energy was found to vary between 0.02 and 0.03 eV. N (E_F) and R_VRH exhibit an interesting composition dependence.     

Effect of Nd substitution on structure and magnetic properties of Nd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> garnet powders

The properties of light rare earth Nd substitution for heavy rare earth Dy in Dy₃Fe₅O₁₂ (DyIG) garnet ferrite have been studied. The Nd _x Dy_3–x Fe₅O₁₂ (x = 0, 0.25, 0.5, 0.75 and 1) (Nd:DyIG) garnet powders were prepared by sol–gel autocombustion followed by heat treatment. The structure and the magnetic properties of the annealed powders were measured with X-ray diffraction (XRD), the Fourier Transform Infrared (FT-IR) and the Physical Properties Measurement System (PPMS) techniques. The experimental results indicate that a single Nd:DyIG garnet phase structure can be obtained after the samples annealed above 800 °C. With the Nd substitution content increasing, the average lattice constants of the sample, the a−d super-exchange interaction strengthens and the magnetization of unit cell increase. The maximum saturation magnetization is 13.86 emu/g for x = 1, and coercive force is about 136 Oe, for x = 0.75. The reason of increasing in magnetization with Nd substitution is also discussed.