Solid-state reactions in the system Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

The formation mechanisms of Li _x Na_{1 ?x} Ta _y Nb_{1 ? y} O₃ perovskite solid solutions in the Li₂CO₃-Na₂CO₃-Nb₂O₅-Ta₂O₅ system have been studied by x-ray diffraction, differential thermal analysis, thermogravimetry, IR spectroscopy, and mass spectrometry at temperatures from 300 to 1100°C. The results indicate that the synthesis of Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions involves a complex sequence of consecutive and parallel solid-state reactions. An optimized synthesis procedure for Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions is proposed.     

Structural and dielectric properties of PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript> solid solutions synthesized at high pressures and temperatures

(1 ? x)PbMg_1/3Nb_2/3O₃ · xPbZrO₃ (1 ? x)PMN · xPZ) solid solutions have been synthesized at a pressure of 5 GPa and temperatures from 1300 to 1700 K, and their structural and dielectric properties have been studied. The composition dependences of the average unit-cell parameter and dielectric permittivity for the solid solutions indicate that the PMN-PZ system has a morphotropic phase boundary near x = 0.65. The solid solutions have a cubic structure for x < 0.65, a rhombohedral structure in the range 0.65 < x < 0.9, and an orthorhombic structure (similar to that of PbZrO₃) for x > 0.9. The temperature and frequency dependences of dielectric permittivity suggest that the (1 ? x)PMN · xPZ samples with x < 0.65 consist of two ferroelectric phases: a relaxor with antipolar dipole order and a normal ferroelectric with a diffuse phase transition. The effect of annealing temperature on the ferroelectric state of the samples with x < 0.65 is examined. In the composition range 0.65 < x < 0.9, the samples have normal ferroelectric properties, independent of annealing temperature.     

Effects of Ge<Superscript>4+</Superscript> acceptor dopant on sintering and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

Lead-free (K_0.5Na_0.5)(Nb_1-xGe _x )O₃ (KNN-xGe, where x = 0-0.01) piezoelectric ceramics were prepared by conventional ceramic processing. The effects of Ge⁴⁺ cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge⁴⁺ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge⁴⁺ cations substituted Nb⁵⁺ ions as acceptors, and the Curie temperature (T_C) shows an almost linear decrease with increasing the Ge⁴⁺ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020°C. Ge⁴⁺ doping less than 0.4 mol.%can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties: piezoelectric constant d₃₃ = 120 pC/N, planar electromechanical coupling coefficient k_p = 34.7%, mechanical quality factor Q_m = 130, and tanδ = 3.6%.     

Preparation and electrical properties of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> solid solutions

Ceramic samples of lead magnesium niobate (PMN) and (1 ? x)Pb(Mg_1/3Nb_2/3)O₃?xPbTiO₃ (PMN-PT) solid solutions with x = 0, 0.05, 0.10, and 0.30 have been prepared by solid-state reactions, and their structural, electrical, and piezoelectric properties have been studied using x-ray diffraction, Rietveld profile analysis, impedance spectroscopy, and the resonance/antiresonance method. The results indicate that the use of nonstoichiometric columbite niobates enables the synthesis of phase-pure PMN and PMN-PT.     

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.     

Effect of Ni Doping at Pd Site in Nb<Subscript>2</Subscript>PdS<Subscript>5</Subscript> Superconductor

The superconducting properties of Nb₂PdS₅ superconductor have been investigated with Ni doping at Pd site All the bulk polycrystalline Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.10) samples are crystallized in singlephase monoclinic structure. The electrical resistivity and magnetic measurements of Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.15) were carried out to study the variation of superconducting critical parameters with Ni doping. Superconductivity in Nb₂PdS₅ sample completely disappears for x ≥ 0.15. We observed that the ratio of upper critical field to transition temperature decreases with increasing Ni concentration. Also, the magnetization study of Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.15) samples shows similar superconducting behaviour. In summary, the superconductivity in Nb₂PdS₅ sample is slightly varying with partial doping of Ni at Pd site in Nb₂PdS₅ superconductor.     

Diffusion phase transition and impedance spectroscopy of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/CuO co-doped BCZT lead-free ceramics

Perovskite type (Ba_0.85Ca_0.15?2x Bi_2x )(Zr_0.1Ti_0.9?x Cu _x )O₃ lead-free ceramics were prepared via a conventional solid-state reaction method. The phase structure, dielectric, ferroelectric properties and complex impedance were investigated in detail. XRD and dielectric measurements determined that single orthorhombic phase displayed in (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ at room temperature. With the introduction of Bi₂O₃/CuO, the phase structure exhibited the mixture of orthorhombic and tetragonal phases, and then turned to single tetragonal phase. In contrast to the sharp dielectric transition of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics, a broad dielectric peak coupled with a slight decrease in Curie temperature was observed in (Ba_0.85Ca_0.15?2x Bi_2x )(Zr_0.1Ti_0.9?x Cu _x )O₃ ceramics with increasing x. The observed diffuse phase transition behavior was further confirmed by a couple of measurements with polarization loops and polarization current density curves. The structural and the composition fluctuations induced by ions doping should be responsible for the diffuse phase transition behavior. Furthermore, physical mechanisms of the conduction and relaxation processes were revealed by using impedance spectroscopy analyses. It was concluded that the conduction and relaxation processes were thermally activated, which was closely linked with the singly and doubly ionized oxygen vacancies.     

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.     

Synthesis and microwave dielectric properties of Zn<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>Nb<Subscript>2</Subscript>O<Subscript>6+<Emphasis Type="Italic">x</Emphasis></Subscript>

We have studied the formation of zinc niobate, ZnNb₂O₆, with the columbite structure and the microstructure and microwave dielectric properties of Zn_1+x Nb₂O_6+x ceramics. The results demonstrate that, in the range 0.005 ≤ x ≤ 0.03, the excess zinc reduces the porosity of the material and increases its microwave quality factor Q. For x ≥ 0.03, the Q of the ceramics decreases because of the formation of an additional, zinc-enriched phase. Sintering in an oxygen atmosphere is shown to improve the dielectric properties of stoichiometric ZnNb₂O₆.     

Structure and electrical properties of MnO doped (Ba<Subscript>0.96</Subscript>Ca<Subscript>0.04</Subscript>)(Ti<Subscript>0.92</Subscript>Sn<Subscript>0.08</Subscript>)O<Subscript>3</Subscript> lead free ceramics

In this work, (Ba_0.96Ca_0.04)(Ti_0.92Sn_0.08)O₃–xmol MnO (BCTS–xMn) lead-free piezoelectric ceramics were fabricated by the conventional solid-state technique. The composition dependence (0 ≤ x ≤ 3.0 %) of the microstructure, phase structure, and electrical properties was systematically investigated. An O–T phase structure was obtained in all ceramics, and the sintering behavior of the BCTS ceramics was gradually improved by doping MnO content. In addition, the relationship between poling temperature and piezoelectric activity was discussed. The ceramics with x = 1.5 % sintering at temperature of 1330 °C demonstrated an optimum electrical behavior: d ₃₃ ~ 475 pC/N, k _p ~ 50 %, ε _r ~ 4060, tanδ ~ 0.4 %, P _r ~ 10.3 μC/cm², E _c ~ 1.35 kV/mm, T _C ~ 82 °C, strain ~0.114 % and \(d_{33}^{*}\) ~ 525 pm/V. As a result, we achieved a preferable electric performance in BaTiO₃-based ceramics with lower sintering temperature, suggesting that the BCTS–xMn material system is a promising candidate for lead-free piezoelectric ceramics.     

Phases and morphotropic regions in the PbNb<Subscript>2/3</Subscript> Mg<Subscript>1/3</Subscript>O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> system

Ceramic samples of solid solutions (1 ? x) PbNb_2/3Mg_1/3O₃ · xPbTiO₃ (0 ≤ x ≤ 1.0, Δx = 0.0025–0.05) are prepared by the columbite method. A detailed x?T phase diagram of the system is constructed (isothermal join at 25°C), and dielectric, piezoelectric, and elastic properties are investigated. It is established that the region of the morphotropic phase transition is positioned in the range 0.28 < x ≤ 0.43 and consists of a series of narrower regions. Inside one phase (cubic, rhombohedral, tetragonal), regions are found in which a qualitative and quantitative difference in structural and electrical parameters is observed. An interpretation of the observed effects in the context of the defect structure of the objects is suggested.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.     

Rare-earth-doped PbTiO<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript> solid solutions

(Pb_{1 ? x} Ln _x )(Zr_0.53Ti_0.47)O₃ and (Pb_{1 ? x} Ln _x )(Zr_0.65Ti_0.35)O₃ (x = 0.02, 0.06; Ln = La, Pr, Gd, Yb) solid solutions have been prepared by modified solid-state synthesis using organic-ligand precursors. The solid solutions have been characterized by thermal analysis, IR spectroscopy, x-ray powder diffraction, and atomic force microscopy. All of them have a rhombohedrally distorted perovskite structure (sp. gr. R3c).     

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.     

Crystallization from high-temperature solutions in the K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied general trends of crystallization from high-temperature solutions in the K₂O-P₂O₅-V₂O₅-Bi₂O₃ system at P/V = 0.5?2.0, K/(P + V) = 0.7?1.4, and Bi₂O₃ contents from 25 to 50 wt % and identified the stability regions of BiPO₄, K₃Bi₅(PO₄)₆, K₂Bi₃O(PO₄)₃, and K₃Bi₂(PO₄)_{3 ? x} (VO₄) _x (x = 0?3) solid solutions. The synthesized compounds have been characterized by X-ray powder diffraction and IR spectroscopy, and the structure of two solid solutions has been determined by single-crystal X-ray diffraction (sp. gr. C ₂/c): K₃Bi₂(PO₄)₂(VO₄), a = 13.8857(8), b = 13.5432(5), c = 6.8679(4) Å, β = 114.031(7)°; K₃Bi₂(PO₄)_1.25(VO₄)_1.75, a = 13.907(4), b = 13.615(2), c = 6.956(2) Å, β = 113.52(4)°.     

Solid-state synthesis,characterization, and properties of Ni<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>-based solid solutions

In this paper, we report the solid-state synthesis, characterization, and physicochemical properties of Ni_4–x Zn _x Nb₂O₉ (x = 0, 0.1, 0.3, 0.5, 0.75, 1.0) zinc-containing nickel niobates and Ni₄Nb_2–x Ta _x O₉ (x = 0.1, 0.3, 0.5, 1.0, 2.0) solid solutions. The materials were characterized by X-ray diffraction. We determined the particle size composition of the synthesized powders, assessed their chemical stability in acid media, obtained IR spectra of the solid solutions, and measured their electrical conductivity as a function of temperature. Some of the solid solutions were used to fabricate and characterize nickel-selective electrodes, which were successfully tested in ion-selective measurements.     

New NaSrPO<Subscript>4</Subscript>:Sm<Superscript>3+</Superscript> phosphor as orange-red emitting material

Sm³⁺-activated NaSrPO₄ phosphors could be efficiently excited at 403 nm, and exhibited a bright red emission mainly including four wavelength peaks of 565, 600, 646 and 710 nm. The highest emission intensity was found for NaSr _1?x PO₄: xSm³⁺ with a composition of x = 0.007. Concentration quenching was observed as the composition of x exceeds 0.007. The decay time values of NaSr_1?x PO ₄ : xSm³⁺ phosphors range from around 2.55 to 3.49 ms. NaSr_1?x PO₄: xSm³⁺ phosphor shows a higher thermally stable luminescence and its thermal quenching temperature T ₅₀ was found to be 350°C, which is higher than that of commercial YAG:Ce³⁺ phosphor and ZnS:(Al, Ag) phosphor. Because NaSr_1?x PO₄: xSm³⁺ phosphor features a high colour-rendering index and chemical stability, it is potentially useful as a new scintillation material for white light-emitting diodes.     

Enhanced magnetoelectric coupling in La-modified Bi<Subscript>5</Subscript>Co<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>Ti<Subscript>3</Subscript>O<Subscript>15</Subscript> multiferroic ceramics

Multiferroic properties of La-modified four-layered perovskite Bi_5?x La _x Fe_0.5Co_0.5Ti₃O₁₅ (0 ≤ x ≤ 1) ceramics were investigated, by analyzing the magnetodielectric effect, magneto-polarization response and magnetoelectric conversion. X-ray diffraction indicated the formation of pure Aurivillius ceramics, and Raman spectroscopy revealed the Bi ions displacement and the crystal structure variation. The enhancement of ferromagnetic and ferroelectric properties was observed in Bi_5?x La _x Fe_0.5Co_0.5Ti₃O₁₅ after La modification. The evidence for enhanced ME coupling was determined by magnetic field-induced marked variations in the dielectric constant and polarization. A maximum ME coefficient of 1.15 mV/cm·Oe was achieved in Bi_4.25La_0.75Fe_0.5Co_0.5Ti₃O₁₅ ceramic, which provides the possible promise for novel magnetoelectric device application.     

Electrical Conductivity and Electrochemical Characteristics of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-Based NASICON-Type Materials

NASICON-type materials with the compositions Na₃V_2–xAl_x(PO₄)₃, Na₃V_{2 - x}Fe_x(PO₄)₃, Na_{3 + x}V_2–xNi_x(PO₄)₃, and Na₃V_{2 - x}Cr_x(PO₄)₃ (x = 0, 0.03, 0.05, and 0.1) have been prepared and characterized by X-ray diffraction analysis, electron microscopy, and impedance spectroscopy. The results demonstrate that the highest electrical conductivity among the samples studied is offered by the material doped with 5% Fe: Na₃V_1.9Fe_0.1(PO₄)₃. The activation energy for low-temperature conduction in the doped materials decreases from 84 ± 2 to 54 ± 1 kJ/mol and that for high-temperature conduction is ~33 kJ/mol. The discharge capacity of Na₃V_1.9Fe_0.1(PO₄)₃/C under typical working conditions of cathodes of sodium ion batteries has been shown to exceed that of Na₃V₂(PO₄)₃/C. The capacity of the more porous material prepared by the Pechini process (Na₃V_1.9Fe_0.1(PO₄)₃/C-{II}) approaches the theoretical one at a low charge–discharge rate and retains its high level as the charge rate is raised (its discharge capacity was 117.6, 108.8, and 82.6 mAh/g at a discharge rate of 0.1C, 2C, and 8C, respectively).     

Synthesis and x-ray diffraction study of solid solutions in the Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript>-Zn<Subscript>2</Subscript>TiO<Subscript>4</Subscript>-Zn<Subscript>2</Subscript>ZrO<Subscript>4</Subscript> system

The multicomponent refractory oxide system Zn₂(Ti_aSn_b)_{1 ? x} Zr_xO₄ (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 1: 0, 2: 1, 3: 1, 4: 1; x = 0?1.0; Δx = 0.05) has been studied by x-ray diffraction, using samples prepared by melting appropriate oxide mixtures in a low-temperature hydrogen-oxygen plasma. Two phases, both with wide homogeneity ranges, have been identified: α-phase, with a cubic inverse spinel structure, and β-phase, with a tetragonal spinel structure. The phase boundaries in the system have been determined. Structural data are presented for about 100 solid solutions of different compositions.