Fabrication of <Emphasis Type="Italic">p-n</Emphasis> junctions in ZnO by arsenic ion implantation followed by annealing in atomic oxygen

We report the properties of p-n junctions produced in ZnO films by As⁺ ion implantation followed by annealing in atomic oxygen. The starting films, n-ZnO〈Ga〉, were grown by magnetron sputtering on amorphous SiO₂ substrates. As shown by x-ray diffraction, the c axis of ZnO is perpendicular to the film surface. The resistivity of the p-ZnO〈As〉 layer is 30–35 Ω cm, carrier mobility 1–2.5 cm²/(V s), and hole concentration 3 × 10¹⁸ cm^?3. The arsenic and gallium concentrations are 2.5 × 10¹⁹ and 1 × 10¹⁸ cm^?3, respectively. The arsenic profile is Gaussian in shape, as shown by secondary ion mass spectrometry. Current-voltage data attest to the presence of an i-layer and to recombination in the space charge region. The barrier height evaluated from current-voltage and capacitance-voltage data is about 3.4 eV, which is comparable to the band gap of ZnO. The electro-and photoluminescence spectra of the junctions show bands at 440 and 510 nm. The 510-nm emission is typical of as-grown n-ZnO〈Ga〉 films. The 440-nm band is attributable to donor-acceptor recombination.     

4<Emphasis Type="Italic">H</Emphasis>-SiC Based Subnanosecond (150 ps) High-Voltage (1600 V) Current Breakers

High-voltage (1600 V) diodes based on epitaxial 4H-SiC p⁺⁺–p⁺–n₀–n⁺ structures are tested as fast current breakers included in a special pulsed circuit. The measured current-breakdown time is about 150 ps. This is a record short time for high-voltage (above 1000 V) silicon-carbide diode breakers. The saturated hole-drift velocity in 4H-SiC of p type is experimentally estimated for the first time: v _sp = 3 × 10⁶ cm/s.     

High-temperature crystal chemistry of Na<Subscript>6</Subscript>(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>

Thermal deformations of Na₆(UO₂)₂O(MoO₄)₄ were studied by high-temperature powder X-ray diffraction. The compound crystallizes in the triclinic system, space group Р\(\bar 1\), a = 7.636(7), b = 8.163(6), c = 8.746(4) Å, α = 72.32(9)°, β = 79.36(4)°, γ = 65.79(5)°, V = 472.74(4) ų. It is stable in the temperature interval 20–700°С. The thermal expansion coefficients (TECs) are α₁₁ = 25.5 × 10^–6, α₂₂ = 7.8 × 10^–6, and α₃₃ = 1.1 × 10^–6 (°C)^–1. The orientation of the TEC pattern relative to the crystallographic axes is a₃₃^Z = 45°, a₃₃^X = 122°, a₂₂^Z = 59°, and a₂₂^X = 66°. The anisotropy of the thermal expansion is due to specific features of the crystal structure of the compound.     

Electrical conductivity of Cs<Subscript>3</Subscript>PO<Subscript>4</Subscript> doped with trivalent cations

Cs_{3 ? 3x} M _x PO₄ (M = Sc, Y, La, Sm, Nd) solid electrolytes have been synthesized, their phase composition has been determined, and their electrical conductivity has been measured as a function of temperature. In all of the systems, we have identified cesium orthophosphate based solid solutions. Above ～550°C, the solid solutions are isostructural with the high-temperature, cubic phase of Cs₃PO₄. They offer high cesium ion conductivity owing to the formation of cesium vacancies via 3Cs⁺ → M³⁺ substitutions and the decrease in phase transition temperature. The conductivity of the synthesized solid solutions, (4.8?5.6) × 10^?3 S/cm at 300°C and (1.6?1.9) × 10^?1 S/cm at 800°C, is at the level of earlier studied Cs_{3 ? 2x} M _x ^II PO₄ solid electrolytes.     

Very high thermal stability with excellent dielectric,and non-ohmics properties of Mg-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4.2</Subscript>O<Subscript>12</Subscript> ceramics

In this work, the nominal CaCu_3?xMg_xTi_4.2O₁₂ (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ)?<?0.009–0.014 and giant dielectric constant (ε′) ～?1.1?×?10⁴–1.8?×?10⁴ with excellent temperature coefficient (Δε′) less than ±?15% in a temperature range of ??60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg²⁺ dopants due to the increase of grain boundary resistance (R_gb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg²⁺ dopants in the structure. In addition, CaCu_3?xMg_xTi_4.2O₁₂ ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (E_b) due to Mg²⁺doping. The high values of ε′ (14012), α (13.64) and E_b (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu_2.90Mg_0.10Ti_4.2O₁₂ ceramic sintered at 1100 °C for 8 h.     

Crystal structure,microstructure and microwave dielectric properties of novel MgAl<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript> ceramic

In the present work, a novel MgAl₂Ti₃O₁₀ ceramic was obtained using a traditional solid-state reaction method. X-ray diffraction and energy dispersive spectrometer showed that the main MgAl₂Ti₃O₁₀ phase was formed after sintered at 1300–1450 °C. With rising the sintering temperature from 1300 to 1450 °C, the bulk density (ρ), relative permittivity (ε _r ) and Q?×?f value firstly increased, reached the maximum values (3.61 g/cm³, 14.9, and 26,450 GHz) and then decreased. The temperature coefficient of resonator frequency (τ _f ) showed a slight change at a negative range of ??94.6 to ??83.7 ppm/°C. When the sintering temperature was 1400 °C, MgAl₂Ti₃O₁₀ ceramics exhibited the best microwave dielectric properties with Q?×?f?=?26,450 GHz, ε _r ?=?14.9 and τ _f ?=???83.7 ppm/°C.     

Synthesis and high-temperature electrical conductivity of Ln<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> and LnYTi<Subscript>2</Subscript>O<Subscript>7</Subscript> (Ln = Dy,Ho)

Ho₂Ti₂O₇ and LnYTi₂O₇ (Ln = Dy, Ho) pyrochlores have been synthesized using hydroxide coprecipitation, mechanical activation, and firing at 1600°C. The bulk and grain-boundary components of their conductivity have been determined for the first time by impedance spectroscopy. The 740°C bulk conductivity of Ho₂Ti₂O₇ is 4 × 10^?4 S/cm, and that of HoYTi₂O₇ is 1 × 10^?3 S/cm, with activation energies E _a = 1.01 and 1.17 eV, respectively, suggesting that these materials are new oxygen-ion conductors. The bulk conductivity of DyYTi₂O₇ (3 × 10^?4 S/cm at 740°C, E _a = 1.09 eV) is almost one order of magnitude lower than that of HoYTi₂O₇ (1 × 10^?3 S/cm at 740°C, E _a = 1.17 eV).     

Effect of sintering temperature on microstructures and microwave dielectric properties of Ba<Subscript>2</Subscript>MgWO<Subscript>6</Subscript> ceramics

The microwave dielectric properties of Ba₂MgWO₆ ceramics were investigated with a view to the use of such ceramics in mobile communication. Ba₂MgWO₆ ceramics were prepared using the conventional solid-state method with various sintering temperatures. Dielectric constants (? _r ) of 16.8–18.2 and unloaded quality factor (Q _u  × f) of 7000–118,200 GHz were obtained at sintering temperatures in the range 1450–1650 °C for 2 h. A maximum apparent density of 6.76 g/cm³ was obtained for Ba₂MgWO₆ ceramic, sintered at 1650 °C for 2 h. A dielectric constant (? _r ) of 18.4, an unloaded quality factor (Q _u  × f) of 118,200 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?34 ppm/°C were obtained when Ba₂MgWO₆ ceramics were sintered at 1650 °C for 2 h.     

Anomalous Impact of Hydrostatic Pressure on Superconductivity of Polycrystalline LaO<Subscript>0.5</Subscript>F<Subscript>0.5</Subscript>BiSe<Subscript>2</Subscript>

We report bulk superconductivity at 2.5 K in LaO_0.5F_0.5BiSe₂ compound through the DC magnetic susceptibility and electrical resistivity measurements. The synthesized LaO_0.5F_0.5BiSe₂ compound is crystallized in tetragonal structure with space group P4/nmm and Reitveld refined lattice parameters are a = 4.15(1) Å and c = 14.02(2) Å. The lower critical field of H _c1 = 40 Oe, at temperature 2 K is estimated through the low field magnetization measurements. The LaO_0.5F_0.5BiSe₂ compound showed metallic normal state electrical resistivity with residual resistivity value of 1.35 m Ω cm. The compound is a type-II superconductor, and the estimated H _c2(0) value obtained by WHH formula is above 20 kOe for 90 % ρ _n criteria. The superconducting transition temperature decreases with applied pressure till around 1.68 GPa and with further higher pressures a high- T _c phase emerges with possible onset T _c of above 5 K for 2.5 GPa.     

Structural,Electrical and Dielectric Properties of Hexa-ferrite-Polyaniline Nano-composites

Ferrite-polyaniline (PANI) composites were prepared by in situ polymerization of polyaniline with the general formula (1 ? x) ferrite + (x) PANI where x = 0, 0.25, 0.5, 0.75, 1. The samples were characterized by XRD, SEM, electrical resistivity, and dielectric measurements. X-ray diffraction reveals single phase formation of CaBaCo₂Al_0.5Fe_11.5O₂₂ Y-type ferrite, whereas polyaniline exhibits an amorphous nature. At room temperature, the resistivity of nano-composites increases with the increase of ferrite filler contents from 3.17 × 10⁴ to 3.19 × 10⁷ Ω cm. Real and imaginary parts of the complex permittivity of the PANI-ferrite composites follow the Maxwell-Wagner model. Based on the Jonscher Law, the AC conductivity of PANI-ferrite composites experiences an increase with the increase in frequency. The exponent calculated from AC conductivity reveals that the hopping is the likely conduction mechanism. The activation energy obtained from temperature-dependent measurements is consistent with room temperature resistivity. Due to the light weight, low cost and flexibility of design, the ferrite-polymer composites are considered useful for microwave devices.     

Influence of Nd doping on microwave dielectric properties of SrTiO<Subscript>3</Subscript> ceramics

Sr_1?x Nd _x TiO₃ (x?=?0.08–0.14) ceramics were prepared by conventional solid-state methods. The analysis of crystal structure suggested Sr_1?x Nd _x TiO₃ ceramics appeared to form tetragonal perovskite structure. The relationship between charge compensation mechanism, microstructure feature and microwave dielectric properties were investigated. Trivalent Nd³⁺ substituting Sr²⁺ could effectively decrease oxygen vacancies. This reduction and relative density were critical to improve Q?×?f values of Sr_1?x Nd _x TiO₃ ceramics. For ε _r values, incorporation of Nd could restrain the rattling of Ti⁴⁺ cations and led to the reduction of dielectric constant. The τ _f values were strongly influenced by tilting of oxygen octahedral. The τ _f values decreased from 883 to 650 ppm/°C with x increasing from 0.08 to 0.14. A better microwave dielectric property was achieved for composition Sr_0.92Nd_0.08TiO₃ at 1460 °C: ε _r ?=?160, Q?×?f?=?6602 GHz, τ _f ?=?883 ppm/°C.     

Understanding of post deposition annealing and substrate temperature effects on structural and electrical properties of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> MOS capacitor

The purpose of this study is to understand the effects of substrate temperature (ST) and post deposition annealing (PDA) on the structural-electrical properties of Gd₂O₃ film and to evaluate the electrical performances of the MOS based devices formed with this dielectric. The Gd₂O₃/Si structures were annealed at 500, 600, 700, and 800 °C under N₂ ambient after the films were grown on heated p-Si substrate at various temperatures ranged from 20 to 300 °C by RF magnetron sputtering. For any given ST, the crystallization/grain size increased with increasing PDA temperature. The bump in the accumulation region or continuous decrease in the capacitance values of the inversion region of the C–V curves for 800 °C PDA was not observed. The lowest effective oxide charge density (Q _eff ) value was obtained to be ??1.13?×?10¹¹ cm^?2 from the MOS capacitor with Gd₂O₃, which is grown on heated Si at 300 °C and annealed at 800 °C. The density of the interface states (D _it ) was found to be in the range of 0.84?×?10¹¹ to 1.50?×?10¹¹ eV^?1 cm^?2. The highest dielectric constant (ε) and barrier height \(({\Phi _B})\) values were found to be 14.46 and 3.68, which are obtained for 20 °C ST and 800 °C PDA. The results show that the negative charge trapping in the oxide layer is generally more than that of the positive, but, it is reverse of this situation at the interface. The leakage current density decreased after 20 °C ST, but no significant change was observed for other ST values.     

Effect of Ni<Superscript>2+</Superscript> substitution on crystal structure and microwave dielectric properties for MgZrNb<Subscript>2</Subscript>O<Subscript>8</Subscript> ceramics

Monoclinic structured Mg_1?xNi_xZrNb₂O₈ (0?≤?x?≤?0.12) ceramics were synthesized for the first time through traditional solid-state reaction process and pure phase were obtained in all range. Rietveld refinement was used to analyze the crystal structure. With the increase of Ni²⁺ substitution amount, ε _r decreased, Q?×?f rose first then fell, τ _f shifted for the positive direction. Bond ionicity, lattice energy and bond energy were separately calculated to investigate the correlations with microwave dielectric properties. Typically, ceramics samples with the composition of Mg_0.92Ni_0.08ZrNb₂O₈ sintered at 1280 °C for 4 h exhibited the optimum microwave dielectric properties: ε _r ?=?24.58, Q?×?f?=?74534.1 GHz, τ _f ?=???49.11 ppm/°C, which could be a promising material for application.     

The calorimetry and thermodynamic functions of Nd Mg<Stack><Subscript>3</Subscript><Superscript>I</Superscript></Stack>Mn<Subscript>4</Subscript>O<Subscript>12</Subscript> (Me<Superscript>I</Superscript>-Li,Na, K) manganites in the range from 298.15 to 673 K

The ceramic technology is employed for synthesizing manganites of composition Nd Mg ₃ ^I Mg₃Mn₄O₁₂(Me^I-Li, Na, K). The X-ray technique is used to find that the compounds crystallize in tetragonal syngony. The parameters of their crystal lattices are determined. Their heat capacities are experimentally determined in the range from 298.15 to 673 K, which enables one to reveal second-order phase transitions. In view of these transitions, equations describing the C _p ^° ～ f(T) dependence are derived, and the thermodynamic functions C _p ^° (T), H°(T)-H°(298.15), S°(T), and Φ ^xx (T) are calculated.     

Electric-field and temperature effects on electric currents in polycrystalline ZnGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>

The current (electrical transport) through In/ZnGa₂Se₄/In structures has been measured as a function of temperature and applied electric field at temperatures from 77 to 400 K in fields from 10 to 3 × 10⁴ V/cm. The results are analyzed in terms of the Poole-Frenkel effect and space-charge-limited currents. The activation energy of traps and trap concentration in ZnGa₂Se₄ and its refractive index are determined to be E _t= 0.8 eV, N _t = 4 × 10¹³ cm^?3, and n = 2.4, respectively.     

Low temperature sintering and microwave dielectric properties of Zn<Subscript>3</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramic

Crystal structure and dielectric properties of Zn₃Mo₂O₉ ceramics prepared through a conventional solid-state reaction method were characterized. XRD and Raman analysis revealed that the Zn₃Mo₂O₉ crystallized in a monoclinic crystal structure and reminded stable up to1020 °C. Dense ceramics with high relative density (~ 92.3%) were obtained when sintered at 1000 °C and possessed good microwave dielectric properties with a relative permittivity (ε _r ) of 8.7, a quality factor (Q?×?f) of 23,400 GHz, and a negative temperature coefficient of resonance frequency (τ _f ) of around ??79 ppm/°C. With 5 wt% B₂O₃ addition, the sintering temperature of Zn₃Mo₂O₉ ceramic was successfully lowered to 900 °C and microwave dielectric properties with ε _r ?=?11.8, Q?×?f?=?20,000 GHz, and τ _f = ??79.5 ppm/°C were achieved.     

Sorption of Molybdenum onto Titanium Hydroxide

Three types of ionic groups with different pK_i values were revealed for T-5 sorbent by potentiometric titration: for acid groups, pK₁ = 7.5 ± 0.5, pK₂ = 10.2 ± 0.5, and pK₃ = 11.0 ± 0.2; for base groups, pK₄ = 6.5 ± 0.2, pK₅ = 4.5 ± 0.2, and pK₆ = 2.7 ± 0.2. Thus, titanium hydroxide is an amphoteric ion exchanger. Each exchange group of T-5 sorbent, characterized by its definite pK_i value, was assigned to a definite hydroxy group. T-5 and T-52 sorbents exhibit high specificity to Mo in acid and neutral solutions. All the isotherms logC_S–logC_L are described by the Langmuir equation for the polyfunctional sorbent for at least two exchange sites in both nitric and sulfuric acid solutions, irrespective of the Mo speciation. Two groups of values were obtained and confirmed for T-5 and T-52 sorbents depending on the Mo concentration: k_d ≈ 10⁴ mL g^–1 at concentrations lower than 10^–5 M and k_d = 1000–2000 mL g^–1 at a concentration of 10^–5 M. The exchangeable hydroxy groups in T-5 sorbent exhibit high heat resistance, and even the sorbent calcined at 900°C preserves certain reliably measurable capacity for Mo. For T-5, the capacity for Mo only slightly depends on the solution acidity and composition and is about ~1 mmol g^–1.     

High-temperature heat capacity and vibrational spectra of Eu<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript>

The Eu₂Sn₂O₇ compound has been prepared by solid-state reaction (by sequentially firing a stoichiometric mixture of Eu₂O₃ and SnO₂ in air at 1273 and 1473 K) and its heat capacity has been determined by differential scanning calorimetry in the temperature range 370–1000 K. The heat capacity data have been used to evaluate the thermodynamic properties of europium stannate: enthalpy increment H°(T)–H°(370 K), entropy change S°(T)–S°(370 K), and reduced Gibbs energy Ф°(T). Raman spectra of Eu₂Sn₂O₇ polycrystals with the pyrochlore structure have been measured in the range 200–1200 cm^–1.     

Surface morphology and thermal figure of merit of a new compound thin film

The third nonlinear optical properties of a new compound 4,4′-bis(3-methoxy benzylidene amino) biphenyl doped poly-methyl methacrylate (PMMA) have been studied using Z-scan technique. Experiments are performed using a continuous waveguide (cw) diode laser at 532 nm wavelength and 0.68 kW/cm² laser intensity. The optical power limiting behavior of sample doped PMMA was also investigated. It also shows a very good optical limiting behavior with a limiting threshold of 4.7 mW. We attribute the nonlinear absorption and optical limiting property of the sample film to two photon absorption effect at 532 nm. The experimental evidences of observing diffraction pattern in compound 4,4′-bis(3-methoxybenzylideneamino) biphenyl doped PMMA has been present. The refractive index change, Δn, and nonlinear refractive index, n ₂ determined from the number of observed ring. We obtained good values of Δn = 105.154 × 10^?4and n ₂ = 154.154 × 10^?7 cm²/W. Variation of refractive index with temperature, dn/dT, and figure of merit, H, are found to be 8.858 × 10^?6 1/°C and 5.316 × 10^?6, respectively. This large nonlinearity is attributed to a thermal effect resulting from linear absorption. Theoretical diffraction pattern that agree well with experimental one are generated using a wave theory.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on the microstructure and electrical properties of LaMnO<Subscript>3</Subscript>-based NTC thermistors

A study to develop a new system of negative temperature coefficient thermistors for wide temperature range, A series of Mn-based perovskite-structured ceramics of composition (LaMn_1?x Al _x O₃)_0.9(Al₂O₃)_0.1 has been synthesized by conventional solid state reaction at 1350?°C. The X-ray diffraction patterns showed that for all the samples, the substitution of manganese by aluminum up to x?=?0.1 preserved the rhombohedral perovskite LaMnO₃-like phase. For x?=?0.2, apart from the LaMnO₃-like structure, a second perovskite phase based on the cubic LaAlO₃ structure was formed. For x?=?0.3 and 0.4, the phase present was LaAlO₃ -type structure. The grain sizes of the sintered body detected by scanning electron microscope were decreased with increasing Al₂O₃ content. The resistivity increases with increasing the Al content. The obtained values of ρ _25?°C and B _25/50 and E _a are in the range of 10–13103 Ω cm, 1813–2794 K, 0.156–0.241 eV, respectively. The resistance variation (ΔR/R) was <0.241% and the minimum value (0.0483%) was obtained for aging at 125?°C at 500 h. The aim of this work was explored new composite ceramics materials, which could be used as potential candidates for wide temperature range from ?100 to 500?°C thermistors applications.