Dielectric properties of Bi4(GeO4)3 and Bi4(SiO4)3

Dielectric constant, dielectric loss and conductivity of Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ single crystals have been measured as a function of frequency and in the temperature range from liquid nitrogen temperature to 400° C. The values of the static dielectric constant at room temperature are 16·4 and 13·7 for Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ respectively. The plots of log (σ) against reciprocal temperature at different frequencies of these crystals merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0·95 eV and 1·2 eV for Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ respectively.     

Structural and dielectric properties of Pb(Li1/4Sm1/4Mo1/2)O3 ceramics

The ceramic samples of lithium-samarium modified lead molybdate, Pb(Li_1/4 Sm_1/4 Mo_1/2)O₃ (PLSM)—a member of ABO₃ family were prepared by solid state reaction technique at ≈ 600–700°C. Preliminary X-ray analysis suggests the formation of single phase orthorhombic compound of PLSM. Studies of surface morphology, uniform particle/grain distribution, and presence of elements in the compound were completed using scanning electron microscope (SEM). Measurements of dielectric constant (ɛ), loss (tanδ) and conductivity (σ) at different frequencies and temperatures provided that the compound has a strong dielectric anomaly at 107°C.     

Phase structure and dielectric property of the ZnNb2O6–(Mg0.3Zn0.7)TiO3 multiphase ceramics

ZnNb₂O₆ and (Zn_0.7Mg_0.3)TiO₃ multiphase ceramics were prepared by conventional mixed-oxide method combined. The phase structure, structure morphology and dielectric properties of multiphase ceramics were investigated. The results show that ZnNb₂O₆ accelerates the decomposition of the hexagonal phase (Zn_0.7Mg_0.3)TiO₃ and a structural transition of columbite ZnNb₂O₆ and rutile to ixiolite ZnTiNb₂O₈ occurs. ZnNb₂O₆–(Zn_0.7Mg_0.3)TiO₃ ceramics have uniform morphology, the grain size becomes smaller with the ZnNb₂O₆ content increasing. ZnTiNb₂O₈ phase and the uniform morphology improve the properties of ceramics, 0.6ZnNb₂O₆–0.4(Mg_0.3Zn_0.7)TiO₃ and 0.8ZnNb₂O₆–0.2(Mg_0.3Zn_0.7)TiO₃ ceramics sintered at 1,000 °C have the best dielectric properties: ε _r  = 25.6–26.5, tanδ = 2.9–5.7 × 10⁻⁴. Due to their good dielectric properties, ZNMT3 and ZNMT4 ceramics can serve as the promising microwave dielectric capacitor.     

A new microwave dielectric ceramics for LTCC applications: Li2Mg2(WO4)3 ceramics

A novel microwave dielectric ceramics Li₂Mg₂(WO₄)₃ (LMW) for low-temperature co-fired ceramics (LTCC) application were prepared by the conventional solid-state sintering method. Densification, phases, microstructure and microwave dielectric properties of the Li₂Mg₂(WO₄)₃ ceramics were investigated. The optimal sintering temperature of dense Li₂Mg₂(WO₄)₃ ceramic approximately ranges from 825 to 875 °C for 3 h. The ceramic specimens fired at 875 °C for 3 h exhibits excellent microwave dielectric properties: ε _r  = 7.72, Q × f = 29,600 GHz (f = 6.0 GHz), and τ _f  = ?15.5 ppm/°C. Moreover, the Li₂Mg₂(WO₄)₃ ceramics has a chemical compatibility with Ag during cofiring, which makes it a promising ceramic for LTCC technology application.     

DC electrical conductivity of CoSiF6·6H2O and (NH4)2SO4

D.C. electrical conductivity of single crystals of (NH₄)₂SO₄ and CoSiF₆·6H₂O have shown conductivity jump near their respective structural transition temperature. Activation energy of (NH₄)₂SO₄ has been found to be consistent with the earlier data. However, CoSiF₆·6H₂O has given prolonged aging effect due to dipolar relaxation and formation of space charge polarisation.σ _true andP _max have been measured.P _max has shown a negative maximum at the transition point. Activation energy of ZnSiF₆·6H₂O has been found to be comparable with CoSiF₆·6H₂O.     

Growth and spectroscopic characteristics of Li2Mg2(MoO4)3 and Li2Mg2(MoO4)3:Co2+ crystals

We have determined the starting mixture composition and process parameters for the growth of bulk, uniform Li₂Mg₂(MoO₄)₃ and Li₂Mg₂(MoO₄)₃:Co²⁺ (1 at %) crystals by a modified Czochralski technique at low temperature gradients (<1°C/cm). The 1500-, 750-, and 600-nm bands observed in the optical absorption spectra of the Li₂Mg₂(MoO₄)₃:Co²⁺ crystals are due to the Co²⁺ ions, which have a 3d ₇ electron configuration and substitute for Mg²⁺.     

Microstructure,dielectric, and energy storage performance of (Zn1/3Nb2/3)4+ complex-ion modified (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics

In this study, (Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)_1-x(Zn_1/3Nb_2/3)_xO₃ ceramics were synthesized by conventional solid-phase methods, referred to as BCZT-xZN (x?=?0.0, 0.1, 0.2, 0.3, 0.4). The effects of adding different contents of (Zn_1/3Nb_2/3)⁴⁺ ion on the microstructure, dielectric and ferroelectric properties of BCZT ceramics were studied. Scanning electron microscopy (SEM) results showed that the average particle size of the samples was significantly reduced after the addition of (Zn_1/3Nb_2/3)⁴⁺ ion, and a second phase appeared when the addition amount was?≥?0.3. The dielectric properties show that with (Zn_1/3Nb_2/3)⁴⁺ ion replacing the B-site of BCZT ceramics, the dielectric constant decreases significantly and the Curie temperature decreases below room temperature. At the same time, we observed that the ceramic has good stability to temperature (-150 °C–200 °C) and frequency (10²–10⁶ Hz) changes. The addition of (Zn_1/3Nb_2/3)⁴⁺ ion can significantly reduce the residual polarization and improve the breakdown strength of ceramics. When x?=?0.3, The maximum energy storage density of ceramics is 0.994 J/cm³, which is about four times higher than that of pure BCZT ceramic (0.25 J/cm³). These findings fully demonstrate the great potential of BCZT ceramics in energy storage.

     

Thermal history induced variable relaxor behavior in the high TC ternary ferroelectric 0.6Bi(Mg1/2Ti1/2)O3–0.05Bi(Zn1/2Ti1/2)O3–0.35PbTiO3

Studies carried out on a perovskite-structured rhombohedral 0.6Bi(Mg_1/2Ti_1/2)O₃–0.05Bi(Zn_1/2Ti_1/2)O₃–0.35PbTiO₃ (xBZT–yBMT–zPT) ceramic quenched from temperatures below 1000 °C show that the dielectric properties are dramatically altered by the thermal history. Samples quenched from temperatures 650 °C–900 °C show classical ferroelectric switching behavior that is not observed on either side of this temperature range. The quenched states lose their switchable ferroelectric properties when heated to temperatures as low as 400 °C. The results demonstrate for the first time that the dielectric and electromechanical response, as observed at room temperature, can be varied between normal to relaxor behavior by changing thermal quenching conditions.     

Enhancing the microwave dielectric properties of Nd (Mg0.5Sn0.5)O3 ceramics by substituting Nd3+ with Ca2+

The microwave dielectric properties of Nd_(1?2x/3)Ca_x(Mg_0.5Sn_0.5)O₃ ceramics were examined to evaluate their exploitation for mobile communication. Nd_(1?2x/3)Ca_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd_2.9/3Ca_0.05(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with the sintering temperature. Nd_2.9/3Ca_0.05(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h had the following properties: a density of 6.86 g/cm³, a dielectric constant (ε_r) of 19.3, a quality factor (Q × f) of 99,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?65 ppm/°C.     

Dielectric, ferroelectric and piezoelectric properties of (1 − x)[Pb0.91La0.09(Zr0.60Ti0.40)O3]–x[Pb(Mg1/3Nb2/3)O3], 0 ≤ x ≤ 1

The dielectric, ferroelectric, and piezoelectric properties of ceramic materials of compositions (1 − x)[Pb_0.91La_0.09(Zr_0.60Ti_0.40)O₃]–x[Pb(Mg_1/3Nb_2/3)O₃], x = (0, 0.2, 0.4, 0.6, 0.8, and 1.0) were studied. The above compositions were prepared by mixing the individual Pb_0.91La_0.09(Zr_0.60Ti_0.40)O₃ (PLZT) and Pb(Mg_1/3Nb_2/3)O₃ (PMN) powders in order to design materials with different combination of piezo and dielectric properties. The powders were calcined at 850 °C for 4 h. The presence of various phases in the calcined powders was characterized by X-ray diffraction (XRD) technique. The compacts were prepared by uniaxial pressing and were sintered at 1250 °C for 2 h. The sintered compacts were electroded, poled at 2 kV/mm dc voltage and their dielectric, ferroelectric, and piezoelectric properties were measured. In general, it was observed that the dielectric constant, loss factor and the slimness of the ferroelectric curves increase with the PMN content while the remnant polarization, saturation polarization, and the coercive fields were decreased. It is now possible to design materials with a wide combination of d ₃₃, K, and loss factor by varying PLZT and PMN ratio.     

Influence of BaZrO3, MnCO3 additives on dielectric properties and microstructure of Ba(Zn1/3Nb2/3)O3 ceramics and Ba(Zn1/3Nb2/3)O3-Sr(Zn1/3Nb2/3)O3 solid solutions

The effect of BaZrO₃, MnCO₃ additives on the dielectric properties, sintering temperature and microstructure of Ba(Zn_1/3Nb_2/3)O₃ (BZN) and Ba(Zn_1/3Nb_2/3)O₃-Sr(Zn_1/3Nb_2/3)O₃ (BSZN) ceramics was studied in this paper. It indicates that both BaZrO₃ and MnCO₃ can lower the sintering temperature of the ceramics and accelerate the crystallization of BZN and BSZN. The dielectric constant ɛ _r increases after MnCO₃ added, but decreases when BaZrO₃ added alone. The existence of MnCO₃ can modulate the temperature coefficient of capacitance τ _c toward positive, while BaZrO₃, can make c more negative. MnCO₃ and BaZrO₃ can restrain the appearance of the second phase; while BaZrO₃, can prevent the appearance of the superstructure. In the BSZN system, when 1 mass % MnCO₃ added, sintering temperature(t _s ) is lowered to 1240°C. In this study, the best sample that has the excellent properties is sample 5 with dielectric properties of ɛ _r = 43.6, τ _c = −8 × 10⁻⁶ °C⁻¹ and tan δ = 0.6 × 10⁻⁴ (1 MHz). The sintering temperature of BZN and BSZN system can be lowered to less than 1300°C.     

Hydrothermal Crystallization in the Systems La2(CO3)3 ? 6H2O-CaCO3(BaCO3)-R-H2O (R = Na2CO3, K2CO3, NaHCO3, KHCO3, NaCl, NH4Cl, CO(NH2)2)

Crystallization in the systems La₂(CO₃)₃ ⋅ 6H₂O-CaCO₃(BaCO₃)-R-H₂O (R = Na₂CO₃, K₂CO₃, NaHCO₃, KHCO₃, NaCl, NH₄Cl, CO(NH₂)₂) was studied under hydrothermal conditions (400–450°C). The solid reaction products were found to contain LaOHCO₃ and NaLa(CO₃)₂. Detailed thermal decomposition schemes were proposed for these phases, and their lattice parameters were refined. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 11, 2005, pp. 1366–1372. Original Russian Text Copyright ? 2005 by Nikol'skaya, Dem'yanets.     

Ultra-high Quality Factor of (Zn2/3Nb1/3)3+ Co-substitution MgAl2O4 Microwave Dielectric Ceramics

Herein, nominal compositions of MgAl_2–x(Zn_2/3Nb_1/3)_xO₄ (x = 0.00, 0.04, 0.08, 0.12, 0.16, 0.20, 0.30, 0.40, and 0.50) ceramics are synthesized using a solid-phase reaction method. The (Mg/Zn)Al₂O₄ solid solution and second-phase Mg₄Nb₂O₉ greatly improve the microwave dielectric properties of the samples. Moreover, the second phase, ionic polarizability, and relative density affect the dielectric constant (ε_r) value. The quality factor (Qf) value is correlated with the packing fraction, achieving a maximum value of ≈563 000 GHz at x = 0.40. The temperature coefficient of the resonant frequency (τ_f) value is negatively correlated with the B-site bond value. When x = 0.40, the nominal composition MgAl_1.6(Zn_2/3Nb_1/3)_0.4O₄ ceramic exhibits good microwave dielectric properties: ε_r = 9.06, ultrahigh Qf = 563 000 GHz, and τ_f = –45 ppm °C⁻¹.     

Influence of Ca0.8Sr0.2TiO3 on the microstructures and microwave dielectric properties of Nd(Mg0.4Zn0.1Sn0.5)O3 ceramics

The influence of Ca_0.8Sr_0.2TiO₃ on the microstructures and microwave dielectric properties of Nd(Mg_0.4Zn_0.1Sn_0.5)O₃ ceramics were investigated by the conventional solid-state method. The X-ray diffraction peaks of (1 − x)Nd(Mg_0.4Zn_0.1Sn_0.5)O₃–xCa_0.8Sr_0.2TiO₃ ceramic system shifted to higher angles as x increased. The dielectric constant increased from 31.8 to 47.7, the quality factor (Q × f) decreased from 54,200 to 42,800 GHz, and the temperature coefficient of resonant frequency (τ _f ) increased from −43 to +41 ppm/°C as x increased from 0.5 to 0.7 when (1 − x)Nd(Mg_0.4Zn_0.1Sn_0.5)O₃–xCa_0.8Sr_0.2TiO₃ ceramic system sintered at 1,600 °C for 4 h.     

Composite dielectrics (1−x)(Mg0.97Zn0.03)2(Ti0.95Sn0.05)O4−xCaTiO3 suitable for microwave applications

(Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄ ceramics by adding CaTiO₃ have been prepared via the solid-state reaction method. The microstructures of samples are systematically studied in order to establish the effects of sintering temperature and additives on microwave dielectric properties of (Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄ ceramics by X-ray diffraction and scanning electron microscopy. A fine combination of microwave dielectric properties (ε_r = 14.57, Q × f = 183,468 GHz, τ_f = ?43.7 ppm/°C) was achieved for (Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄ ceramics sintered at 1,390 °C for 4 h. CaTiO₃, as a τ_f compensator, was added to form a temperature-stable ceramic system. For (1?x) (Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄?xCaTiO₃ system, 0.93(Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄?0.07CaTiO₃ ceramic sintered at 1,390 °C had optimal dielectric properties (ε_r = 18.32, Q × f = 94,715 GHz, τ_f = ?4.1 ppm/°C) which satisfied microwave applications in resonators, filters and antenna substrates.     

Dielectric and piezoelectric properties of Pb(Ni1/3Nb2/3)O3–PbTiO3–PbZrO3 ceramics modified with bismuth and zinc substitutions

The dielectric and piezoelectric properties of the (Pb_0.985Bi_0.01)(Ni_1/4Zn_1/12Nb_2/3)_x- (Zr_σTi_1-σ)_1-xO₃ piezoelectric ceramic system (0.2 ≤ x ≤ 0.7, 0.1 ≤ σ ≤ 0.9) were systematically investigated. The results showed that, after poling, the dielectric constant, ε ₃₃ ^T , increased for the tetragonal compositions but decreased for the rhombohedral compositions. Furthermore, high values of ε ₃₃ ^T and piezoelectric modulus, d ₃₁ were found for the compositions along the extension of the morphotropic phase boundary. The highest values of the planar electromechanical coupling factor, K _p, and the piezoelectric modulus, d ₃₁, were found to be 0.70 and − 274 × 10^-12 C N^-1, respectively. The Curie temperature, remanent polarization, coercive field and the lattice constants of the a and c axes in relation to the Pb(Ni_1/3Nb_2/3)O₃ content and the Zr/Zr + Ti ratio were also determined. This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

A zinc phosphate, [NH3(CH2)3NH3][Zn4(PO4)2(HPO4)2], possessing alternate inorganic and organic layers

A new zinc phosphate of the formula, [NH₃(CH₂)₃NH₃][Zn₄(PO₄)₂(HPO₄)₂], has been synthesized hydrothermally starting from a zinc amine complex. It crystallizes in the monoclinic space group C2/c; a=17.279(1), b=5.193(1), c=20.115(1) Å, β=92.6(1)°; V=1803.1(2) ų; Z=4; D_calc=2.05 g cm⁻³; μ (MoKα)=5.62 mm⁻¹. The final R, and wR₂=0.037, 0.093 obtained for 136 observed data [I>2σ(I)]. The structure consists of macroanionic sheets of interconnected ZnO₄ and PO₄ tetrahedra in the ab plane. The sheets are held together by hydrogen bond interactions with the organic structure-directing amine, forming alternate inorganic–organic layers in this material. Hydrogen bond interactions between the inorganic layers, via the terminal –OH group, leads to the formation of pseudo one-dimensional channels.     

Preparation of Pb(Zr,Ti)O<Subscript>3</Subscript>–Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by dry–dry method

Ternary perovskite ceramics of Pb[(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x]_0.98Nb_0.02O_3.01 (PZTMN, x = −0.075, −0.05, −0.025, 0, 0.025, 0.05, and 0.075 ), are synthesized via dry–dry method. B-site precursors of PZTMN ([(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x ]_0.98Nb_0.02O_2.01, ZTMN) can be synthesized via a two-step solid state reaction method. The first calcination temperature is 1,300 °C, and the second is not higher than 1,360 °C. Incorporation of magnesium and niobium ions promotes the formation of the single phase solid solution with ZrTiO₄ structure. Single phase perovskite PZTMN is formed at 780 °C, much lower than that in conventional process. Dense ceramics can be sintered at about 1,260 °C with dielectric and piezoelectric properties comparable to that of wet–dry method and higher than that of conventional method. It seems that B-site precursor method is cost effective in preparation of ternary piezoelectric ceramics.     

Effect of preparation methods on microstructures and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

Effect of preparation methods on microstructures and microwave dielectric properties of Ba(Mg_1/3Nb_2/3)O₃ ceramics was investigated. Ba(Mg_1/3Nb_2/3)O₃(BMN) ceramics were prepared by the conventional mixed oxides method and the molten salt synthesis method. It was shown that the single-phase of BMN was obtained at 900 °C in the molten salt synthesis method. No single-phase BMN was obtained in the conventional mixed oxides method, although the calcining temperature was increased up to 1400 °C. BMN powders prepared by the molten salt synthesis method had better sinterability than that prepared by the conventional mixed oxides method. Because of the very different nature of the powders, different microstructures were observed. The molten salt synthesis method ceramics have a higher B-site ordering parameter (S) and larger grain size than that of the conventional mixed oxides ceramics at same sintering temperature. The variation of Qf, ε _r and τ _f were also explained based on the difference in microstructures.