Synthesis,phase confirmation and electrical properties of (1 − x)KNNS−xBNZSH lead-free ceramics

Journal of Materials Science: Materials in Electronics - In the present work, lead-free piezoelectric ceramics (Rx)(K0.5Na0.5)(Nb0.96Sb0.04O3)?x(Bi0.5Na0.5)(Zr0.8Sn0.1Hf0.1)O3 [abb. as...     

Tl1−xIn1−xSnxSe2 (x = 0, 0.1, 0.2, 0.25) single-crystalline alloys as promising non-linear optical materials

Novel materials for the infrared two-photon absorption—Tl_1?xIn_1?xSn_xSe₂ single crystals (x = 0, 0.1, 0.2, 0.25) were grown. Their optoelectronic properties including two-photon absorption at wavelength equal to 9.4 μm at different temperatures were studied. From the spectral data it was established that band gap energy increases with increasing SnSe₂ content in the solid solutions reaching its maximum for the largest content (x = 0.25). The infrared two photon absorption has achieved its maximal value at x = 0.1. The temperature dependence of the optical band gap at various compositions in the range of 77–300 К is practically linear. The band gap value decreases with the increase of T causing the spectral shift of the absorption edge to the low-energy region. Additionally X-ray photoelectron core-level spectra for pristine and Ar⁺-ion irradiated surfaces of Tl_1?xIn_1?xSn_xSe₂ single crystals have been measured.     

New Pb-Based 1222 Cuprates, (Pb0.5B0.5)Sr2(RE2−x−y Ce x Sr y )Cu2O z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y)

New Pb-based layered cuprates with the 1222 structure have been synthesized in the (Pb_0.5B_0.5)Sr₂ (RE_2−x−y Ce _x Sr _y )Cu₂O _z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single-phase samples in the systems can be obtained for a nominal composition of x=0.7 and y=0.1. The crystal structure of the samples has a tetragonal symmetry, the lattice parameters of a and c are increasing with increasing the ionic radius of RE element. Despite treatment under high O₂ pressure of 100 atm, the samples are semiconductors with the transport process characteristic of three-dimensional variable range hopping conduction.     

Rietveld analysis, magnetic, vibrational and impedance properties of (Bi1−xPrx)(Fe1−xZrx)O3 ceramics

(Bi_1?xPr_x)(Fe_1?xZr_x)O₃ ceramics with x = 0.03, 0.06 and 0.10 were prepared via solid state reaction route. X-ray diffraction and Raman spectra of the ceramics were recorded for calculating its lattice parameters and structural analysis. Magnetic studies indicated a significant enhancement in magnetization of (Bi_1?xPr_x)(Fe_1?xZr_x)O₃ ceramics with maximum remnant magnetization of 0.12 emu g^?1 for x = 0.06 sample. Fourier transform infrared spectra and Rietveld analysis confirmed the change in bond length arising due to Pr and Zr codoping. Dielectric measurements showed dielectric anomaly around Neel temperature, indicating magnetoelectric coupling in the samples as well as the dielectric relaxation for higher doping. The effect of Pr and Zr codoping on the impedance and modulus behavior of BiFeO₃ lattice is discussed. The frequency dependence of electric modulus and impedance of the material show the presence of non-Debye relaxation in the samples. All samples showed energy band gap in the range 2.16–2.0 eV, indicating possibility of optical activity in visible range and making it suitable for photocatalytic applications.     

Synthesis,microstructure and properties of (Ti1−x,Mox)2AlC phases

The reaction path of the (Ti_0.9, Mo_0.1)₂AlC phase from Ti, Al, TiC and Mo powder mixtures was investigated in detail ranging from 500 to 1450°C, and the results show that the reaction between Ti and Al produced Ti–Al intermetallics, and the reaction between Al and Mo formed Mo–Al intermetallics. And then the (Ti_0.9, Mo_0.1)₂AlC phase was formed by the reaction of Ti–Al, Mo–Al intermetallics, and TiC. At 1350°C for 2?h, a dense (Ti_0.9, Mo_0.1)₂AlC phase with purity was successfully fabricated. The Vickers hardness, flexural strength and fracture toughness were 5.48?GPa, 363.60?MPa and 5.78?MPa m^1/2, which were improved by 44, 34 and 136% for (Ti_0.80, Mo_0.20)₂AlC, respectively, compared with the single-phase Ti₂AlC.     

Electrochemical performance of (La,Sr)(Co,Fe)O3−δ–(Ce,Sm)O2−θ–CuO composite cathodes for intermediate temperature solid oxide fuel cells

La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ–CuO composite cathodes were studied for the potential application in intermediate temperature solid oxide fuel cells. Ce_0.8Sm_0.2O_2?θ electrolyte with porous Ce_0.8Sm_0.2O_2?θ interlayer was successfully prepared by one-step sintering process. The effect of interlayer between cathode and electrolyte and CuO on the electrochemical performance of the composite cathodes was investigated by AC impedance spectroscopy. The application of interlayer decreased the area specific resistance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode. The addition of CuO to La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ reduced the phase formation temperature of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ by 150 °C and the addition of CuO to La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode reduced the optimal calcination temperature of the cathode to 800 °C. The composite cathode with 2 mol% CuO calcined at 800 °C exhibited the lowest area specific resistance of 0.05 Ω cm² at 700 °C in air, which was reduced by 67% compared with that of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode. The studies of the corresponding single cell performance, thermal expansion and thermal cycling behaviors further indicated that the composite cathode with 2 mol% CuO could be a promising cathode material.     

N2O decomposition over (Mg6−xAx) MnO8 (A = Li, Al)

Two different murdochite-type mixed oxides, (Mg_6–x Li _x )MnO₈ (x = 0, 0.1, 0.2 and 0.3) and (Mg_6–x Al _x )MnO₈ (x = 0, 0.2, 0.4, 0.6) were examined for the catalytic decomposition of N₂O in order to make clear the effects of mixed valencies of pairing manganese ions and oxygen vacancies. The valence of manganese ions and the amount of surface oxygen vacancies have been examined with X-ray photoelectron spectroscopy (XPS). (Mg_6–x Li _x )MnO₈ had mixed valence manganese ions and oxygen vacancies on the surface after the substitution. The substituted (Mg_6–x Al _x )MnO₈ had a mixed valence state but oxygen vacancies decresed with x and excess oxygen over stoichiometry was observed at x = 0.4 and 0.6. The reaction rate of N₂O decomposition increased after substitution with lithium but hardly increased after the substitution with aluminum in (Mg_6–x A _x )MnO₈. We assumed that the presence of oxygen vacancies on the surface along with pairing altervalent manganese ions affected strongly to enhance the reactivity of N₂O decomposition.     

Grain growth in (Ca1−x,Mg x )Zr4(PO4)6 ceramics

Grain growth in (Ca_1–x ,Mg _x )Zr₄(PO₄)₆ (CMZP) ceramics in the final stage of sintering has been investigated. The grain growth in CMZP ceramics obeys the isothermal grain-growth kinetics with time exponent,n, lying between 1.8 and 2.4 which depends on magnesium content, indicative of a change in grain-growth rate. The time exponent for the grain growth of CMZP can be taken as 2.0 which implies that a normal grain growth develops in the CMZP ceramics. The apparent activation energy for grain growth demonstrates a maximum atx = 0.0 and a minimum atx = 0.1, with 103.2 and 39.4 kcal mol^–1, respectively, indicating that a small amount of magnesium promotes grain-boundary migration. The critical grain size for initiating microcracks in the CMZP increases with increasing magnesium and reaches 9–12 m whenx = 0.4.     

Static bismuth disorder in Bi2−x(CrTa)O7−y

The crystal structure of the pyrochlore Bi_2−x(CrTa)O_7−y has been refined by the Rietveld method from powder neutron and synchrotron X-ray diffraction data. Using the ideal pyrochlore structural model, anomalously high atomic displacement parameters (APD), which could not be satisfactorily explained with anisotropic ADP, of both Bi and O′ sites were observed. The structure was successfully refined with a model that incorporated static displacive disorder of both the Bi and O′ atoms. Using this model physically reasonable ADP parameters for both the Bi and O′ atoms, and improvement in the various measure of fit were obtained. The underbonding of the Bi atoms, observed in ideal pyrochlore model, but removed in the disordered structure, is believed to be the main driving force for this disorder.     

Superstructures exhibited by oxides of the aurivillius family, (Bi2O2)2+ (An−1BnO3n+1)2−

Bi₅Ti₃FeO₁₅ and Bi₇Ti₃Fe₃O₂₁ which are n=4 and n=6 members of the family of oxides of the general formula (Bi₂O₂)²⁺(A_n−1B_nO_3n+1)²⁻ show unusual superstructures, possibly due to cation ordering.     

Role of Gd content in Cu(1) and Cu(2) sites on electrical, microstructural, physical, mechanical and superconducting properties of YBa2Cu3−xGdxO7−δ ceramics

This study deals with the effects of partial Gd³⁺ substitution for the Cu sites on the electrical, microstructural, physical, mechanical and superconducting properties of YBa₂Cu_3?xGd_xO_7?δ ceramic superconductors with x = 0, 0.025, 0.050, 0.100 and 0.150 with the aid of dc resistivity, transport critical current density (J _c ), X-Ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-Ray (EDX), Vickers microhardness (H _v ) and density measurements. The samples studied in this work are prepared by the standard solid-state reaction method. The resistivity (at room temperature), critical (onset and offset) temperature, variation of transition temperature, critical current density, hole-carrier concentration, grain size, phase purity, lattice parameter, texturing, surface morphology, element distribution, density, porosity, crystallinity, Vickers microhardness and elastic modulus (E) values of the samples are obtained and compared with each other. The obtained results show that the room temperature resistivity systematically increases with the increment of the Gd content as a result of the hole filling when the onset (T _c ^onset ) and offset (T _c ^offset ) critical temperatures determined from the resistivity curves are found to decrease from 95.2 to 93.6 K and 92.0 to 83.3 K, respectively, showing the presence of impurities and weak links between the superconducting grains. As for the critical current density measurements, the J _c values decrease from 132 to 34 A/cm² as the Gd doping increases. The XRD results give that although the Gd³⁺ ions substituted tend to occupy both the Cu(1) and Cu(2) sites, the ions are more favorable for the Cu(2) site as a consequence no change of the crystal structure. Besides, the peak intensities belonging to major phase (Y123) decrease monotonously with the increment of the Gd content in the system; however, new peaks belonging to the minor phases start to appear after the doping level of x = 0.0250 beyond which these peaks enhance monotonously, resulting in the decrement of the grain size. Further, the Lotgering indices calculated from the XRD patterns indicate that the texturing of the Y123 grains reduces systematically with the Gd content. According to the SEM investigations, the microstructures of the samples prepared degrade slightly with the content up to the doping level of x = 0.025 after which the morphology suddenly deteriorates due to the appearance of the different phases in the system. EDX measurements show that not only do the elements used for the preparation of the Y123 superconductors with and without Gd content distribute homogeneously but also the level of Cu element rapidly decreases with the increment of the Gd content compared to the other elements, illustrating that the Cu²⁺ ions may partly be substituted by Gd³⁺ ions. Moreover, the porosity analyses for the samples depict that the porosity increases with the Gd content, leading to the degradation of the grain connectivity. We also discuss on the mechanical properties of the samples to examine both the elastic modulus and the strength of connection between superconducting grains.     

Fabrication of n-Zn1−xGaxO/p-(ZnO)1−x(GaP)x thin films and homojunction

Ga doped ZnO (GZO) and GaP codoped ZnO (GPZO) thin films of different concentrations (1–4 mol%) have been grown on sapphire substrates by RF sputtering for the fabrication of ZnO homojunction. The grown films have been characterized by X-ray diffraction (XRD), photoluminescence (PL), Hall measurement, energy dispersive spectroscopy (EDS), time-of-flight secondary ion mass spectrometer (ToF-SIMS), UV–Vis–NIR spectroscopy and atomic force microscopy (AFM). Unlike in conventional codoping, here we directly doped (codoped) GaP into ZnO to realize p-ZnO. The Hall measurements indicate that 2 and 4% GPZO films exhibit p-conductivity due to the sufficient amount of phosphorous incorporation while all the monodoped GZO films showed n-conductivity as expected. Among the p-ZnO films, 2% GPZO film shows low resistivity (2.17 Ωcm) and high hole concentration (1.8 × 10¹⁸ cm^?3) by optimum incorporation of phosphorous due to best codoping. Similarly, among the n-type films, 2% GZO shows low resistivity (1.32 Ωcm) and high electron concentration (2.02 × 10¹⁹ cm^?3) by optimum amount of Ga incorporation. The blue shift and red shift in NBE emission observed from PL acknowledged the formation of n- and p-conduction in monodoped and codoped films, respectively. The neutral acceptor bound exciton recombination (A⁰X) observed by low temperature PL for 2% GPZO confirms the p-conductivity. Further, the high concentration of P atoms than Ga observed from ToF-SIMS (2% GPZO) also supports the p-conductivity of the films. The fabricated p–n junction with best codoped p-(ZnO)_0.98(GaP)_0.02 and best monodoped n-Zn_0.98Ga_0.02O films showed typical rectification behavior of a diode. The diode parameters have also been estimated for the fabricated homojunction.     

Diamagnetic and Electrical Properties of Si x Mo2S3−x (x=0.1, 0.2, 0.33, 0.5) and A0.1Mo2S3−x (A=C, B, and Ru)

Mo₂S₃ doped with Si, C, B, and Ru, is identified to bear the same crystalline structure P2₁/m as that of Mo₂S₃ through XRD analysis. Diamagnetic transitions with χ _m ～10^?4 emu/g?Oe at temperature ranging from 2 K to 6 K were observed in the doped samples of Si _x Mo₂S_3?x (x=0.1, 0.2, 0.33, 0.5). And both of the x=0.2 and 0.5 samples were found to have double diamagnetic transitions with higher T _c at the same temperature of 6.01 K, while Si _x Mo₂S_3?x of x=0.33 displayed an extra ferromagnetic-like response at 63 K. The corresponding transition in resistivity of Si _x Mo₂S_3?x with x=0.1 was noticed to show a mild drop with less than 10 % of its original transition values as measured down to 2 K. But a superconducting-like magnetic field dependence on the phase transition of resistivity was also noted. Its diamagnetic signals were greatly reduced when the applied magnetic fields were raised to 10³ Oes. In the doped samples of A_0.1Mo₂S_2.9 (A=C, B, and Ru), the phase transition in resistivity at 4.08 K, 4.62 K, and 4.35 K, respectively, exhibited similar fashion as that in the case of Si_0.1Mo₂S_2.9.     

Self-driven solar-blind ultraviolet photodetectors based on p-Zn1−xSbxO/n-Si− (x = 0.03, 0.05) heterojunction diodes

Journal of Materials Science: Materials in Electronics - Ultra-violet photodetectors based on p-ZnO/n-Si? heterojunctions have been fabricated by radio-frequency magnetron sputtering...     

High-pressure synthesis of a new homologous series of superconductors, (Hg1−xTIx)2Ba2Can−1CunOy (0.3 ≤ x ≤ 0.6,n=3,4)

We have recently synthesized new superconducting cuprates containing a mercury-based bilayer, i.e. (Hg,Tl)₂Ba₂(Ca,Y)Cu₂O_y and (Hg_1–x Tl_x)₂Ba₂ Ca_n–1 Cu_nO_y (x 0.4, n = 3,4) by a high-pressure technique. These compounds are the n=2, 3 and 4 members of a new homologous series, (Hg, Tl)-22(n–1)n. The effects of Tl substitution for Hg on the formation and superconductivity of the (Hg, Tl)-2223 and -2234 phases are investigated. Both the phases are stabilized for the Tl content x of 0.3–0.6. T_c of the as-synthesized (Hg,Tl)-2223 compound increases from 45 K to 81 K with an increase in x. In contrast, T_c of the (Hg,Tl)-2234 compound is almost independent of x (114 K).     

Critical thermistors based on VnO2n−1 (n=3−6)

New types of critical thermistors are proposed, based on V₃O₅, V₄O₇, V₅O₉, and V₆O₁₁. It is shown that they can be prepared from Magnelli-phase single crystals, which do not decompose during the phase change. Volt-ampere characteristics and switching voltage-temperature curves were obtained.     

Growth and characterization of Ba(Mn,Ti)xFe12−xO19 crystals

Crystals of BaMn_xTi_yFe_12−(x+y)O₁₉ were grown by spontaneous nucleation in slowly cooled high temperature solutions (HTS method). Bi₂O₃, BaB₂O₄, Na₂O and NaFeO₂ were tested as fluxing salts and the crystallization conditions and the growth results are reported, as a function of different fluxes. Distribution coefficients of elements were deduced from the crystal stoichiometry measured by atomic absorption and microprobe analysis. Crystal structure, lattice parameters, and Curie temperature of crystals were also determined. They were found to be similar to those of polycrystals having the same chemical composition.     

Photoconductivity in single crystals of (TlGaSe2)1−x(TlInS2)x alloys (0−0.45 ≤ x ≤0.55-1)

The spectral distribution of the photoconductivity in (TlGaSe₂)_1−x(TlInS₂)_x single crystals has been studied at 77 K and 300 K. At O ≤ x ≤ 4, Eg is observed to vary linearly with x. Eg(x) deviates from linearity at x = 0.6. This deviation is attributed to the effect of disorder in the composition. Over the range 0.6 to 2.2 eV pronounced impurity photoconductivity is detected at 77 K and 300 K. Deep impurity levels and their neighbourhood in this alloy are established to preserve their positions with the variation in the composition. The analysis of the obtained results indicates that the impurity centres are mainly connected with the cation neighbourhood.     

Two-photon absorption of Tl1−xIn1−xSnxSe2 (x = 0, 0.1, 0.2, 0.25) single crystalline alloys and their nanocrystallites

Two-photon absorption (TPA) of Tl_1−xIn_1−xSn_xSe₂ (x = 0, 0.1, 0.2, 0.25) was studied at CO₂ laser wavelength 9.4 μm with pulse duration 1 μs. The studies were performed at different temperatures and for the nanocrystallite sizes varying within the 7–200 nm. The nanocrystals were fabricated by mechanical milling with simultaneous acoustical field treatment and porous filter size separation. The studies have shown that the TPA may be enhanced during the decrease of the nanocrystallite sizes below 50–60 nm. There exists also some critical x value at which the TPA value begin substantially to increase. The comparison with other chalcogenide crystals is performed. The studied nanocrystallites are relatively stable to the infrared laser treatment and are not hygroscopic which allow to use them in different IR optoelectronic devices.     

Growth of perfect-crystal Si-Si1−x Gex-(Ge2)1−x (InP)x structures from the liquid phase

Structures comprising Si-Si_1−x Ge_x-(Ge₂)_1−x (InP)_x with an intermediate Si_1−x Ge_x buffer layer were grown on silicon substrates. Morphological examinations, scanning patterns and diffraction spectra, and also the electrophysical and luminescence properties of the heterostructures were used to show that the crystal perfection of these structures depends on the choice of liquid-phase epitaxy conditions. Pis’ma Zh. Tekh. Fiz. 25, 37–40 (December 26, 1999)