Temperature annealing of radiation defects in xCu2Se-(1 − x)As2Se3 glasses: Dependence on composition

The temperature annealing of radiation defects (RDs), which are broken bonds of network atoms, has been studied for a number of glasses of quasi-binary system xCu₂Se-(1 ? x)As₂Se₃ γ-irradiated at 77 K. The density distributions of localized states caused by defects have been determined based on the temperature dependences of the relative intensity I(T)/I(77) of the EPR spectrum of RDs and according to the energy of the thermal release of D(E); and it was found that their shape is close to Gaussian. There is a significant shift in the curves of I(T)/I(77) to lower temperatures with increasing Cu content in the network. In glasses with copper, the width of D(E), and the density of localized states increase with increasing x. It is assumed that the dependence of E ^m (x) (E ^m —energy, which corresponds to the maximum of the distribution of D(E)), correlates with the change in the negative effective interelectron correlation energy U _eff on x. In As₂Se₃ glasses, in the temperature range of 77 to ～175 K, values of I(T)/I(77) > 1 are observed, which was explained by the appearance of thermally induced defects.     

Mandelshtam–Brillouin Scattering in As2S3 and GeS2 Chalcogenide Glasses

Mandelshtam–Brillouin and Rayleigh scattering in As₂S₃ and GeS₂ chalcogenide glasses is investigated. Longitudinal hypersonic velocities, adiabatic elastooptical constants (p ₁₂) _ad at frequencies 15 GHz, extinction coefficients, and scattering losses are determined.     

Density and surface tension of Se(90−0.9x )S(10−0.1x)Me x and Se(60−0.6x)S(40−0.4x)Me x (Me = Sb), Ge glass-forming meltsMe x (Me = Sb), Ge glass-forming melts

The properties of melts in the Se_(90−0.9x)S_(10−0.1x)Me _x and Se_(60−0.6x)S_(40−0.4x)Me _x (Me = Sb, Ge) systems (wherex ranges from 2.5 to 15 mol % with a step of 2.5 mol %) have been investigated. The density and surface tension of melts and the wetting angles of the PbSe semiconductor by melts are measured. The work of adhesion and adhesion strength of the glass coating are calculated. The experimental data are processed using the least-squares method, and the corresponding regression equations are derived. From the materials of the paper reported at the International Conference “Glasses and Solid Electrolytes” (St. Petersburg, 1999, May 17–19).     

New scheelite-type Cd1−3x⌷xGd2x(MoO4)1−3x(WO4)3x ceramics – their structure,thermal and magnetic properties

Polycrystalline samples of scheelite-type Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x solid solution with limited homogeneity (0<x≤0.25) and cationic vacancies (denoted as ⌷) have successfully prepared by a high-temperature annealing of CdMoO₄/Gd₂(WO₄)₃ mixtures composed of 50.00 mol% and less of gadolinium tungstate. Initial reactants and obtained ceramic materials were characterized by XRD, simultaneous DTA–TG, and SEM techniques. A phase diagram of the pseudobinary CdMoO₄–Gd₂(WO₄)₃ system was constructed. The eutectic point corresponds to 1404±5 K and ~70.00 mol% of gadolinium tungstate in an initial CdMoO₄/Gd₂(WO₄)₃ mixture. With decreasing of Gd³⁺ content in a CdMoO₄ framework, the melting point of Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x increases from 1406 (x=0.25) to 1419 K (x=0.0833), and next decreases to 1408 K (x=0). EPR method was used to identify paramagnetic Gd³⁺ centers in Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x for different values of x parameter as well as to select biphasic samples containing both Cd_0.25⌷_0.25Gd_0.50(MoO₄)_0.25(WO₄)_0.75 and Gd₂(WO₄)₃.     

Glass Formation and Luminescence of Glasses in the Ga2S3–GeS2–Nd2S3System

The results of spectral measurements and the differential thermal analysis (DTA) data for glasses in the Ga₂S₃–GeS₂–Nd₂S₃system are presented. The boundaries of the glass formation region in the Ga₂S₃–GeS₂–Nd₂S₃system are determined. It is shown that the luminescence efficiency increases with an increase in the gallium sulfide content due to the displacement of the concentration quenching boundary of Nd³⁺luminescence with a change in the glass matrix composition.     

Synthesis and structure of [{As(NtBu)3}2Li6] containing an [As(NtBu)3]3− trianion

Attempts to prepare the [As(N^tBu)₃]³⁻ trianion by the reaction of As(NMe₂)₃ with [^tBuNHLi]_n (1:3 monomer equiv.) proved unsuccessful. However, if the reaction is carried out with an excess of ^tBuNH₂ (3 equiv.) the target complex [{As(N^tBu)₃}₂Li₆] (1) is obtained. This is the first example of a complex containing an [As(NR)₃]³⁻ trianion.     

Raman spectra and extended X-ray absorption fine structure characterization of La(2−x)/3NaxTiO3 and Nd(2−x)/3LixTiO3 microwave ceramics

A-site deficient perovskite compounds, La_(2?x)/3Na_xTiO₃ (0.02 ≤ x ≤ 0.5) and Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.5) microwave ceramics, were investigated by Raman scattering. Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.5) was also investigated by extended X-ray absorption fine structure (EXAFS) measurement. The Raman shifts of the E (239 cm^?1) and A₁ (322 cm^?1) modes of La_(2?x)/3Na_xTiO₃ were found to decrease with x. However, the E (254 cm^?1) and A₁ (338 cm^?1) of Nd_(2?x)/3Li_xTiO₃ were found to blueshift with x, which was caused by Li substitution. The redshift of the A₁ (471 cm^?1) phonon of Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.3) indicates that O–Ti–O bonding forces lessen with Li concentration, which is consistent with the EXAFS result that Ti–O bond lengths increase for 0.1 ≤ x ≤ 0.3. For x > 0.3, the EXAFS result shows that Ti–O bond lengths decrease. Moreover, Ti–O bond lengths show strong correlation with the microwave dielectric constants of Nd_(2?x)/3Li_xTiO₃.     

Correlation between local structure variations and critical temperature of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(TiO2)x superconductor

TiO₂ doping content affects the critical temperature (T_c) and the variations of local structure on Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ. The (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ)_1-x(TiO₂)_x samples were fabricated with the solid-state reaction process, where x = 0, 0.002, 0.004, 0.006, 0.008, and 0.01. The T_c values of the samples were obtained by measuring resistivity versus temperature, indicating that T_c gradually decreased with increasing doping content (x). To explain the obtained degradation of T_c, carrier properties, role of interlayer coupling, and local structure were systematically investigated using Azlamozov–Larkin theory and its Lawrence–Doniach modification for strong anisotropic superconductors. The calculation of excess conductivity at the mean field region showed that the c-axis coherence length (ξ_c) and the effective inter-layering spacing (d) increased with increasing doping content. X-ray diffraction patterns also showed that the bond distances increased with increasing TiO₂ content. The copper valence (V) and carrier concentration (p) of the samples were determined by analyzing the Cu L_2,3-edge X-ray absorption near edge structure spectra. The values of V and p showed the same trend of decreasing with increasing x. A close correlation between the changes in local structure parameters and degradation of T_c of (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ)_1-x(TiO₂)_x was then probably concluded.     

Low temperature Mössbauer spectroscopic study of CaO(Fe2O3)1−x(Al2O3)x system

Low temperature ⁵⁷Fe Mössbauer spectroscopic studies on CaO(Fe₂O₃)_1−x(Al₂O₃)_x, written as CF_1−xA_x, have been carried out. In view of the earlier findings based on room temperature data, the spectra have been analysed by assuming three Fe sites: two belonging to CF phase and the third site for the Fe atoms distributed in the CA phase. The Fe sites pertaining to the CF phase experience hyperfine field of about 49T and 47T, respectively, at 20K; whereas the third site is paramagnetic at this temperature.     

Varistor and electrical properties of MgO.(Fe2O3)1−x(Bi2O3)x ceramics

In this study, MgO.(Fe₂O₃)_1−x(Bi₂O₃)_x (x = 0.01, 0.02, 0.04, 0.08) samples were prepared by the conventional ceramic process. Microstructure studies revealed that the samples contain MgFe₂O₄ grains surrounded by insulating Bi₂O₃-rich phases. DC electrical resistivity of the samples was increased by Bi₂O₃ content up to 1.1 MΩ.cm for the sample with x = 0.08. Current density- electric field investigations suggested that the samples with x = 0.01, 0.02 and 0.04 exhibited varistor properties. The sample with x = 0.01 showed excellent varistor properties with a non-linear coefficient of 45 and a threshold electric field value of 160 V/cm. Variation of D.C electrical conductivity versus temperature indicated that the activation energy values for the conduction were increased by Bi₂O₃ content from 0.334(5) eV to 0.857(5) eV. A.C electrical conductivity spectra of the samples obey the universal power law and the charge transport mechanism is based on electron hopping via sudden translational motion between the ferric and ferrous ions.     

Discovery of the Griffiths phase in the quaternary nitrides Ge1−xSnxNFe3

We report the Griffiths phase (GP) and transport behavior in the quaternary antiperovskite nitrides Ge_1−xSn_xNFe₃ by a series of systematical magnetic susceptibility and thermoelectric behavior measurements. All the corresponding fitting exponent parameters λ_GP = 0.852 and 0.854 completely satisfy 0 ≤ λ ≤ 1 in GP regions for Ge_0.7Sn_0.3NFe₃ and Ge_0.8Sn_0.2NFe₃, respectively, indicating the different ferromagnetic concentrations in the system. An observed structural transition from distorted tetragonal structure (I4/mcm) to cubic antiperovskite (Pm3m) with increasing dopants should be responsible for the GP in Ge_1−xSn_xNFe₃, which results in a magnetic phase transition from ferromagnetism (FM) to antiferromagnetism (AFM). Furthermore, the studies of electrical transport properties indicate that the Ge_1−xSn_xNFe₃ series of compounds perform a Fermi liquid behavior at low temperature while the stronger electron-phonon scatterings are found in the high-temperature region. In addition, the intensive electron–electron correlation is also determined since much higher value of lattice thermal conductivity κ_l than the one of electronic thermal conductivity κ_e.     

High resolution neutron powder diffraction study of the microstrain contribution in Pb(ZrxTi1−x)O3 ceramics

The high-resolution neutron powder diffraction data collected from Pb(Zr_xTi_1-x)O₃ (x=0.20, 0.52, 0.53 and 0.54) samples between 4 and 900 K were analysed using Rietveld refinement. The high-resolution powder diffractometer (HRPD) at Rutherford Appleton Laboratory (ISIS facility) was used. Particular attention was paid to two phase coexistence in the vicinity of the morphotropic phase boundary and to the microstrain contribution. Strongly reflection indices (h,k,l) dependent line broadening was related to a spatial variation of x which probes the sensitivity of different crystal lattice spacings against x.     

A thioacetamide interlayer anchoring TiO2 and (FAPbI3)1−x(MAPbBr3)x for high-performance perovskite solar cells

In the perovskite solar cells (PSCs), traps of the perovskite film or interface are the research focus, which can severely hinder charge transfer and benefit charge recombination, thus weakening the photoelectric performance of the devices. Herein, a Thioacetamide (TAA) interfacial layer is used to passivate the traps of PSCs. Comparing to the control device (17.65%), the TAA-based solar cells can achieve an enhanced efficiency of 19.14%. It is found that the passivation caused by TAA occurs through the interactions of sulfur in TAA with undersaturated Pb in perovskite and Ti⁴⁺ in TiO₂, resulting in a faster and more efficient charge transfer and a greatly reduced trap density from 3.36 × 10¹⁶ cm⁻³ to 1.93 × 10¹⁶ cm⁻³. It is shown that the modification method using TAA may be helpful for passivating traps and obtaining excellent photoelectric properties of PSCs.     

Doping and luminescence mechanisms of broadband NIR-II emitting Zn2(1−x)Ni2xGa3Ge0.75O8 nanoparticles

In this study, Zn_2(1−x)Ni_2xGa₃Ge_0.75O₈ (x = 0.0002, 0.001, 0.002, 0.010, 0.020, and 0.030) nanoparticles with broadband NIR-II emissions were synthesized by a hydrothermal synthesis combined with a vacuum annealing. For the Ni²⁺-doped ZGGO samples (x = 0–0.03), with increasing concentration, the particle shape gradually becomes spherical and the average particle size decreases from 124.4 to 74.2 nm. Meanwhile, for the ZGGO:Ni²⁺_0.01 nanoparticles, the asymmetrically broad emission peak around 1290 nm, which is the superposition of the two peaks locating at 1280 and 1450 nm, can be observed and the afterglow time exceeds 30 min. Based on the spectral data, luminescence decay curves, first-principles calculations, and Tanabe–Sugano theory, it is found that Ni²⁺ ions can occupy not only tetrahedral but also octahedral Zn²⁺ sites (locating in anti-site defects pair) in the spinel ZGGO host, and they have the contributions to the 1450 and 1280 nm emission peaks, respectively. Furthermore, the surface-modified ZGGO:Ni²⁺ nanoparticles exhibited good stability in the H₂O and HSA (5% human serum albumin, pH = 7.4) solutions and the occurred agglomeration sinking in the SLS (simulate lysosomal solution, pH = 4.7) solution. Compared to the narrow-band NIR-II emitting persistent luminescence nanoparticles (ZGGO:Cr³⁺,Er³⁺ and ZGGO:Cr³⁺,Nd³⁺), broadband NIR-II emitting persistent luminescence nanoparticles (ZGGO:Ni²⁺ NIR-II) possess stronger persistent luminescence intensity and can effectively avoid the water absorption of biological tissues. Our results suggest that ZGGO:Ni²⁺ persistent luminescence nanoparticles have a potential to become optical probes for deep-tissue autofluorescence-free bioimaging in the biomedical field.     

Magnetic properties of ferrites-cobaltites Bi1 − x La x Fe1 − x Co x O3 (1.0 ≥ x ≥ 0.7) with a perovskite structure

The molar magnetic susceptibility (χ_mol) of Bi_{1 ? x} La _x Fe_{1 ? x} Co _x O₃ solid solutions (x = 1.0, 0.9, 0.8, or 0.7) with a crystal structure of rhombohedrally distorted perovskite (R $\bar 3$ c) has been investigated in the temperature range of 5–300 K in a 0.86 T magnetic field. In the temperature range where χ_mol depends on temperature T according to the Curie-Weiss law, the resulting effective magnetic moments of Fe³⁺ and Co³⁺ ions ( $\mu _{eff,Fe^{3 + } ,Co^{3 + } ,} \mu _{eff,Fe^{3 + } } $ and $\mu _{eff,Co^{3 + } } $ ) have been determined for the solid solutions under study. Fe³⁺ ions in the solid solutions have been found to be in the mixed intermediate spin (IS) and high spin (HS) states ( $\mu _{eff,Fe^{3 + } } $ is 4.26μ_B and 4.68μ_B for the temperature range of 5–100 and 150–300 K, respectively). It is shown that 8% Co³⁺ ions in LaCoO₃ at 5–19 K are in the paramagnetic IS state and they determine to a great extent the magnetic susceptibility. It is established that only 9% and 18% Co³⁺ ions in Bi_{1 ? x} La _x Fe_{1 ? x} Co _x O₃ solid solutions (x = 0.9 or 0.8) are in the paramagnetic IS state in the temperature ranges of 5–30 and 5–110 K, respectively, while the other ions are diamagnetic.     

Electrical,structural and thermal properties of nanoceramic (Bi2O3)1−x−y(Ho2O3)x(Tm2O3)y ternary system

Ho₂O₃ and Tm₂O₃ doped Bi₂O₃ composite electrolyte type materials for solid oxide fuel cells (SOFCs) operating at intermediate-temperature were investigated. The bismuth-based ceramic powders were produced by using conventional solid-state synthesis techniques. The products were characterized by means of scanning electron microscopy (SEM), X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), and the four-point probe technique (4PPT). XRD and DTA/TG measurements indicate that all of the samples have the stable fluorite type face centered cubic (fcc) δ-phase. 4PPT measurements were performed in the temperature range 150–1000 °C in air and these measurements showed that the electrical conductivity of the samples decrease with increasing amount of Tm₂O₃. This increase in the electrical conductivity of the samples could be attributed to the increase in the numbers of highly polarizable cations and oxide ion vacancies. The highest conductivity value was found as 5.31×10^?1 Ω cm^?1 for the (Bi₂O₃)_1?x?y(Ho₂O₃)_x(Tm₂O₃)_y ternary system (for x=20 and y=5 mol%) at 1000 °C. The activation energies of the samples were calculated from log σ graphics versus 1000/T. These calculated results showed that the translation motion of the charge carriers, oxygen vacancies, and space charge polarizations are responsible for the change in activation energy as a function of temperature.     

Synthesis and lithium ionic conductivity of Li3−2x(In1−xZrx)2(PO4)3 (0≦x≦0·20)

Lithium ion conductors, Li_3−2x(In_1−xZr_x)₂(PO₄)₃ (0≦x≦0·20), were synthesized by a solid state reaction. A superionic conductive phase of Li₃In₂(PO₄)₃ was stabilized down to room temperature, assisted by the substitution of Zr⁴⁺ for In³⁺ sites of Li₃In₂(PO₄)₃. TG-DTA analysis indicated no phase transition in the samples with x superior to 0·05. The substituted samples showed much higher ionic conductivity by a couple of magnitude than that of Li₃In₂(PO₄)₃. In particular, the highest conductivity at room temperature was 1·42×10⁻⁵ Scm⁻¹ for Li_2·8(In_0·9Zr_0·1)₂(PO₄)₃. Thin films with the composition of Li_2·8(In_0·9Zr_0·1)₂(PO₄)₃ was prepared by a sol–gel method. A coating solution was made from lithium isopropoxide, indium isopropoxide, zirconium isopropoxide and diphosphorus pentaoxide. Well crystallized films were obtained on silicon dioxide and quartz glass substrates by dropping the coating solution, followed by firing over 873 K. In the temperatures above 473 K the lithium ionic conductivity of the film was slightly higher than that of sintered samples prepared by the solid state reaction at 1373 K.     

Structural and ion transport properties of [(AgI)x(AgBr)0.4−x](LiPO3)0.6 and (AgBr)x(LiPO3)(1−x) solid electrolytes

The (AgBr)_x(LiPO₃)_(1−x) (x=0.4 and 0.5) and [(AgI)_x(AgBr)_0.4−x](LiPO₃)_0.6 (x=0.1, 0.2, and 0.3) superionic electrolytes have been prepared by conventional melt quenching using a twin roller. These electrolytes are characterized by X-ray diffraction, SEM, and energy dispersive X-ray analysis (EDAX) for structural investigation. Electrical characterizations have been carried out by the AC impedance analysis. The conductivity of LiPO₃ glassy system at room temperature is improved by doping with the silver bromide (AgBr)_x(LiPO₃)_(1−x) and the mixture of silver iodide, silver bromide (AgI-AgBr-LiPO₃ system) up to 10⁻⁵ and 10⁻³ Ω⁻¹ cm⁻¹, respectively (improvements by four or five orders of magnitude). The frequency response of ionic conductivity has been analyzed by universal dynamic response model (Jonscher's law) and AC conductivity data are fitted using the Jonscher's power law. The conductivity values obtained by the power law and impedance plots are comparable. The frequency exponent (n) has a value between 0 and 1. The AgI-AgBr-LiPO₃ system shows the mixed alkali effect. Summerfield scaling master curve is temperature dependent, which may be due to the contribution of the both lithium and silver ions to ionic conduction.