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%.     

Strong up-conversion luminescence and electrical properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> multifunctional ceramics by Er<Superscript>3+</Superscript> doping

Novel green-emitting piezoelectric ceramics of SrBi_4?x Er _x Ti₄O₁₅ (SBT-xEr) were prepared. Strong up-conversion with bright green (524 and 548 nm) and a relatively weak red (660 nm) emission bands were obtained under 980 nm excitation at room temperature, which is attributed to the intra 4f–4f electronic transition of (²H_11/2, ⁴S_3/2)–⁴I_15/2 and the transition from ⁴F_9/2 to ⁴I_15/2 of Er³⁺ ions, respectively. Simultaneously, Er³⁺ doping promotes the electrical properties. At 0.8 mol%Er, the optimal electric properties with high Curie temperature of T _c?~527?°C, large remanent polarization of 2P _r?~14.92 μC/cm² and piezoelectric constant of d ₃₃?~17 pC/N was achieved. As a multifunctional material, Er³⁺ doped SBT showed a great potential to be used in 3D-display, bio-imaging, solid state laser and optical temperature sensor.     

Upconversion Luminescence of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocrystals Doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> Ions

The upconversion luminescence (UCL) of nanocrystalline gadolinium oxide (Gd₂O₃) doped with Er³⁺ and Yb³⁺ ions has been studied in the temperature range of 90–400 K. The nanocrystals were synthesized by chemical vapor deposition and possessed a cubic crystalline structure with an average particle size within 48–57 nm. It is established that the USL intensity in the red (⁴F_9/2 → ⁴I_15/2 transition in Er3+ ion) and green (⁴S_3/2 → ⁴I_15/2 transition) spectral regions depends on the sample temperature and concentration of dopant ions, as well as on the additional structural defects (anion vacancies) created in the crystal lattice by the introduction of Zn²⁺ ions or irradiation with high-energy (10 MeV) electrons. The luminescence efficiency and spectrum of the upconversion phosphor are determined by energy transfer processes.     

New,thermally stable Gd<Subscript>11</Subscript>(GeO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>O<Subscript>10</Subscript>-based upconversion phosphors

A series of Gd_11–x–y Yb _x Er _y GeP₃O₂₆ germanate phosphates differing in the ratio of the Yb³⁺ and Er³⁺ active ions have been synthesized, and their luminescence spectra have been measured. According to X-ray diffraction characterization results, all of the synthesized germanate phosphates are single-phase and have a triclinic structure (sp. gr. P1). We have measured upconversion luminescence spectra due to the Er^{3+ 2}H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 radiative transitions in the synthesized gadolinium ytterbium erbium germanate phosphates and determined the luminescence upconversion energy yield (B _en) in Gd_11–x–y Yb _x Er _y GeP₃O₂₆. The effects of the concentrations and ratio of the dopants in the Gd₁₁(GeO₄)(PO₄)₃O₁₀ germanate phosphate host on B _en and the ratio of the luminescence intensities in the red and green spectral regions (R/G) have been assessed.     

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.     

Magnetic properties of LaInO<Subscript>3</Subscript>-based perovskite-structure photoluminescent materials doped with Nd<Superscript>3+</Superscript>, Cr<Superscript>3+</Superscript>, and Mn<Superscript>3+</Superscript> ions

Single-phase ceramic samples of La_1–xNd_xInO₃ (0.007 ≤ x ≤ 0.05), LaIn_0.99M_0.01O₃, and La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺) solid solutions have been prepared by solid-state reactions, and their crystal structure, magnetic field dependences of their specific magnetization at 5 and 300 K, and temperature dependences of their molar magnetic susceptibility have been studied. It has been shown that the 300-K specific magnetization of the La_1–xNd_xInO₃ (x = 0.02, 0.05), La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺), and LaIn_0.99Mn_0.01O₃ solid solutions increases linearly with increasing magnetic field strength up to 14 T and that the magnitude of the 300-K specific magnetization of the La_0.993Nd_0.007InO₃ and LaIn_0.99Cr_0.01O₃ solid solutions increases linearly, but they have diamagnetic magnetization. At a temperature of 5 K, the magnetization of all the indates studied here increases nonlinearly with increasing magnetic field strength, gradually approaching magnetic saturation, without, however, reaching it in a magnetic field of 14 T. In the temperature range where the Curie–Weiss law is obeyed (5–30 K), the effective magnetic moments obtained for the Nd³⁺ ion (\({\mu _{effN{d^{3 + }}}}\)) in the La_1–xNd_xInO₃ solid solutions with x = 0.007, 0.02, and 0.05 are 2.95μ_B, 3.09μ_B, and 2.75μ_B, respectively, which is well below the theoretical value \({\mu _{effN{d^{3 + }}}}\)= 3.62μ_B. The effective magnetic moments of the Cr³⁺ and Mn³⁺ ions in the LaIn_0.99Cr_0.01O₃ and LaIn_0.99Mn_0.01O₃ solid solutions are 3.87μ^B and 5.11μ^B, respectively, and differ only slightly from the theoretical values \({\mu _{effC{r^{3 + }}}}\)= 3.87μ^B and \({\mu _{effM{n^{3 + }}}}\)= 4.9μ^B.     

Influence of isovalent and heterovalent substitution for Bi<Superscript>3+</Superscript> and Fe<Superscript>3+</Superscript> on the properties of Bi<Subscript>2</Subscript>Fe<Subscript>4</Subscript>O<Subscript>9</Subscript>-based solid solutions

Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites have been prepared by solid-state reactions at a temperature of 1073 K. X-ray diffraction data indicate that, in the Bi_2–хLa_хFe₄O₉ system, the limiting degree of La³⁺ substitution for Bi³⁺ ions in Bi₂Fe₄O₉ does not exceed 0.05 and that the limiting degree of substitution in the Bi₂Fe_4–2xTi_xCo_xO₉ system lies in the range 0.05 < x < 0.1. The specific magnetization and specific magnetic susceptibility of the samples have been measured at temperatures from 5 to 300 K in a magnetic field of 0.86 T. The field dependences of magnetization obtained for the Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites at temperatures of 300 and 5 K demonstrate that partial isovalent substitution of La³⁺ for Bi³⁺ ions in Bi₂Fe₄O₉ and heterovalent substitution of Ti⁴⁺ and Co²⁺ ions for two Fe³⁺ ions leads to partial breakdown of the antiferromagnetic state and nucleation of a ferromagnetic state.     

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.     

Properties of fluorine-doped PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> ceramics

We report the first fluorine doping of lead magnesium niobate in the PbMg _{(1 + x)/3}Nb_{(2 ? x)/3}O_{3 ? x} F _x system in a wide composition range, x = 0.025 to 0.625. The fluorine content of the samples is shown to be substantially lower than the intended one because of the fluorine volatilization in the form of HF during synthesis and sintering in air. The ceramics consist of magnesium and lead oxides undetectable by x-ray diffraction, and a perovskite phase whose composition can be represented by the formula PbMg_{(1 + m)/3}Nb_{(2 ? m)/3}O_{3 ? m} F _m , where the fluorine content after sintering is m ≤ 0.12. The PbO and MgO contents of the ceramics depend on the starting mixture composition (x) and heat-treatment conditions (hydrogen fluoride and lead oxide volatilization). As a result of the low fluorine content, the diffraction patterns of the samples show no superlattice reflections, and their lattice parameter varies insignificantly with x. Data are presented on the temperaturedependent dielectric permittivity of ceramic samples sintered and annealed under different conditions.     

NaF induced enhancement of luminous efficiency in narrow-band red-emitting K<Subscript>2</Subscript>TiF<Subscript>6</Subscript>:Mn<Superscript>4+</Superscript>@NaF phosphors

A series of K₂TiF₆:xMn⁴⁺ @NaF samples were prepared by the cation exchange method in HF solution. Coating effects of NaF on the fluorescent properties of the samples were discussed. It is interesting that NaF has induced enhancement of luminous efficiency for the samples. Mechanism of NaF induced enhanced luminescence effect was suggested. That is that the enhancement effect of NaF coating is mainly attributed to a suitable local distortion of the crystal field surrounding the Mn⁴⁺ activator through doping with NaF. The results indicate that the optimal conditions are x?=?0.07 and w_NaNO3?=?2.5 g. Decay lifetime and the photoluminescence quantum yield of the optimal sample are 5.25 ms and 99.19?±?0.03%, respectively. The chromaticity coordinates of the optimal sample are x?=?0.6926, y?=?0.3073. So, the phosphor emits deep red light, which can be applied for blue light-based white LED.     

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.     

Effect of Ho-doping on structural,electrical and magnetic properties of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> ceramics prepared by Plasma-Activated Sintering

Different components of La_0.7?x Ho _x Sr_0.3MnO₃ (LHSMO, x = 0, 0.1, 0.2, 0.3) ceramics were fabricated by Plasma-Activated Sintering (PAS), so as to study the correlation between the contents of Ho³⁺ and the structural, electrical, magnetic properties. XRD and SEM confirmed that LHSMO ceramics prepared by PAS exhibited high-purity phase and dense microstructure. The measurement of electrical resistivity showed that the resistivity of LHSMO ceramics increased, and the metal–insulator transition temperature decreased with the increasing Ho-doping content. The resistivity data were then fitted using various empirical equations, and the conduction mechanism of LHSMO ceramics was found to be in accord with the electron–magnon scattering process in the low-temperature region and the small polaron hopping model in the high-temperature region. Lastly, we calculated the values of magnetoresistance of the LHSMO ceramics, which increased with increasing Ho-doping content, from 3.5% for x = 0 to 14.6% for x = 0.3. Therefore, the doping of Ho³⁺ into La_0.7Sr_0.3MnO₃ can effectively enhance the low-field magnetoresistance effect.     

Sr<Subscript>3</Subscript>GdLi(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F: Sm<Superscript>3+</Superscript> phosphor: preparation and luminescence properties evaluation

A series of Sr₃Gd_1?xLi(PO₄)₃F: xSm³⁺ (x?=?0.02, 0.04, 0.06, 0.08) phosphors were synthesized by a high-temperature solid state method. The Sm³⁺ activated Sr₃GdLi(PO₄)₃F phosphors can be efficiently excited by the wavelengths in the range from 350 to 450 nm, which matches perfectly with that of the commercial near-UV LED chips. The optimal doping concentration of Sr₃Gd_1?xLi(PO₄)₃F: xSm³⁺ phosphors was determined to be x?=?0.04, corresponding to the quantum efficiency of 2.23%, and the CIE chromaticity coordinates (x?=?0.5172, y?=?0.4641). The concentration quenching mechanism of Sm³⁺ in Sr₃GdLi(PO₄)₃F host is mainly attributed to the dipole–dipole interaction, which was confirmed by the fluorescent lifetimes. The effect of temperature on the photoluminescence property of Sr₃GdLi(PO₄)₃F: Sm³⁺ was investigated. 90% of the intensity is preserved at 150 °C. In addition, a white light emitting diode (WLED) lamp was fabricated by a 405 nm n-UV LED chip coated with Sr₃Gd_0.96Li(PO₄)₃F:0.04Sm³⁺ phosphor and commercial yellow phosphor (YAG: Ce³⁺) of a certain mass ratio. The present work indicates that the Sr₃GdLi(PO₄)₃F: Sm³⁺ orange–red-emitting phosphors tend to be potential application in n-UV WLED.     

Structure,dielectric and ferroelectric properties of lead free (K,Na)(Nb)O<Subscript>3</Subscript>-xBiErO<Subscript>3</Subscript> piezoelectric ceramics

The effect of BiErO₃ (BE) as a doping material on the structural, dielectric and ferroelectric properties of (KNa)NbO₃ ceramics was explored in this research. Co-existence of two phase regions was confirmed in the composition range at x?=?0.5% and x?=?1.0%. The addition of BE content led to a decrease of the grain size and the ceramics became denser. Bulk P–E hysteresis loops were obtained with a maximum polarization of P _max = 30.56 µC/cm² and a remnant polarization of P _r = 25.10 µC/cm², along with a coercive field of E _c  ~ 11.26 kV/cm. The results revealed that a field strain value of ~?0.26 for x?=?0.5% of BE substitution was attained. This presents outstanding piezoelectric and dielectric properties.     

Temperature effect on the photoluminescence intensity and Eu<Superscript>2+</Superscript> excited state lifetime in EuGa<Subscript>2</Subscript>S<Subscript>4</Subscript> and EuGa<Subscript>2</Subscript>S<Subscript>4</Subscript>:Er<Superscript>3+</Superscript>

The photoluminescence (PL) spectra and Eu²⁺ excited state lifetime of EuGa₂S₄ and EuGa₂S₄:Er³⁺ have been studied in the range 78–500 K. The spectra show a band at 545 nm, due to the 4f ⁶5d → 4f ⁷(⁸ S _7/2) transition. With increasing temperature, the full width at half maximum Γ(T) of the PL band of EuGa₂S₄ and EuGa₂S₄:Er³⁺ crystals increases from 0.15 to 0.22 and from 0.13 to 0.19 eV, respectively. Over the entire temperature range studied, Γ(T) is a linear function of T ^1/2. The 545-nm emission intensity and Eu²⁺ excited state lifetime in EuGa₂S₄ and EuGa₂S₄:Er³⁺ vary exponentially with temperature. The luminescence quenching energies evaluated from the Arrhenius plots of I(10³/T) and τ(10³/T) coincide (0.10 eV) within the error of determination.     

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 Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the microstructure and electrical properties of (Ba,Ca)(Zr,Ti)O<Subscript>3</Subscript> lead-free ceramics

Lead-free ceramics (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃?x wt.%Cr₂O₃ (BCZT-xCr) were prepared via the conventional solid-state reaction method. The microstructure and electrical properties of BCZT-xCr samples were systematically studied. XRD and Raman results showed that all samples possessed a single phased perovskite structure and were close to the morphotropic phase boundary (MPB). With the increase of the Cr content, the rhombohedral-tetragonal phase transition temperature (T _R-T) increases slightly, and the Curie temperature (T _C) shifts towards the low temperature side. XPS analysis reveals that Cr³⁺ and Cr^{5 +} ions co-existed in Cr-doped BCZT ceramics, indicating the different impact on the electrical properties from Cr ions as “acceptor” or “donor”. For the x = 0.1 sample, relative high piezoelectric constants d ₃₃ (～316 pC/N) as well as high Q _m (～554) and low tanδ (～0.8%) were obtained. In addition, the AC conductivity was also investigated. Hopping charge was considered as the main conduction mechanism at low temperature. As the temperature increases, small polarons and oxygen vacancies conduction played important roles.     

Ionic conductivity of BaF<Subscript>2</Subscript> + ZnF<Subscript>2</Subscript> + CdF<Subscript>2</Subscript> + YbF<Subscript>3</Subscript> optical fluoride ceramic

The electrical conductivity of an optical fluoride ceramic in the quaternary system BaF₂ + ZnF₂ + CdF₂ + YbF₃ has been determined in the temperature range 338–722 K using impedance spectroscopy (5 to 5 × 10⁵ Hz). The 500-K ionic conductivity of the ceramic is σ = 3.3 × 10^–4 S/cm, which corresponds to the electrical characteristics of single crystals of the best conducting nonstoichiometric M_1–x R _x F_{2 + x} (M = Sr, Ba; R = La–Nd; x = 0.3–0.5) fluorite phases. We have observed nonmonotonic variation (breaks) in temperature-dependent σ, which is due to competing fluoride ion transport processes in different parts of the ceramic sample. The highly conductive state of the BaF₂ + ZnF₂ + CdF₂ + YbF₃ fluoride ceramic seems to be due to the formation of structural regions corresponding to a Ba_1–x Yb _x F_{2 + x} solid solution.     

Improvement of the Magnetization of Barium Hexaferrites Induced by Substitution of Nd<Superscript>3+</Superscript> Ions for Fe<Superscript>3+</Superscript> Ions

Barium hexagonal ferrites (BaNd _x Fe_12?x O ₁₉) have been synthesized by initial high-energy milling of the precursors and calcining subsequently. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). XRD and SEM examinations reveal that a high-crystallized hexagonal BaNd _x Fe_12?x O ₁₉ with lamellar morphology is obtained when the precursor is calcined at 1200^°C in air for 3 h. The hexagonal crystalline structure of BaFe₁₂ O ₁₉ is not changed after doping Nd³⁺ ions in BaFe₁₂ O ₁₉. However, lattice parameters a and b values increase with an increase in Nd content at first, then decrease. Nd substitution may improve the magnetic properties of BaNd _x Fe_12?x O ₁₉. BaNd_0.1Fe_11.9 O ₁₉, obtained at 1050^°C, has the highest specific saturation magnetization value (80.81 emu/g) and magnetic moment (16.21 μ _B); BaNd_0.2Fe_11.8 O ₁₉, obtained at 950^°C, has the highest coercivity value, 4075.19 Oe.     

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.