Preparation and properties of ceramics based on (Na0.5Bi0.5)1 ? xAxTiO3 (A = Sr, Cd) solid solutions

This paper describes the preparation and properties of (Na_0.5Bi_0.5)_{1 − x} A _x TiO₃ (A = Sr, Cd) lead-free ferroelectric ceramics. The (0.63–0.66)Na_0.5Bi_0.5TiO₃ · (0.37–0.34)Sr_0.7Bi_0.2TiO₃ ceramics are shown to have the best dielectric and piezoelectric properties: tanδ = 0.013–0.009, ɛ_RT = 1200–1500, d ₃₁ = (370–400) × 10⁻¹² C/N, and k _ρ = 0.4–0.58. The cadmium-containing ceramics offer low dielectric losses and high dielectric permittivity at room temperature.     

Structural and dielectric properties of Na1?xBaxNb1?x(Sn0.5Ti0.5)xO3 ceramics

Lead-free (1 − x)NaNbO₃/xBa(Ti_0.5Sn_0.5)O₃ (x = 0.1, 0.125, 0.15, 0.175, 0.2, and 0.3) ceramics were elaborated by the conventional ceramic technique. Sintering has been made at 1523 K for 2 h. The crystal structure was investigated by X-ray diffraction with CuKα radiation at room temperature. As a function of composition, these compounds crystallize with tetragonal or cubic symmetry. Dielectric measurements show that the materials have a classical ferroelectric behavior for compositions in the range 0.10 ≤ x ≤ 0.15 and relaxor one for compositions in the range 0.15 < x ≤ 0.30. Temperatures T _C or T _m decrease as x content increases. The ferroelectric behavior has been confirmed by hysteresis characterization. For x = 0.1, a piezoelectric coefficient d ₃₁ of 42.146 pC N⁻¹ was obtained at room temperature. The evolution of the Raman spectra was studied as a function of temperature for x = 0.1.     

Na0.5Bi0.5TiO3纳米纤维的制备及形成机理研究

以Bi(NO3)3 5H2O、板状钛酸(H1.07Ti1.73O4 nH2O)、NaOH为原料,采用水热法合成了具有钙钛矿结构的Na0.5Bi0.5TiO3纳米纤维.利用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)、透射电镜(TEM)和X射线能谱仪(EDS)对产物进行表征.通过考察在200℃下水热反应不同时间的产物的相结构、微观形貌及化学组成,对Na0.5Bi0.5TiO3纳米纤维的形成机理进行了探讨.结果表明:钛酸H1.07Ti1.73O4 nH2O是一类具有层板结构的化合物,在水热反应过程中,板状钛酸的层间H3O+可与Na+、Bi3+进行离子交换,通过原位生长的方式形成了板状Na0.5Bi0.5TiO3颗粒,随着水热反应的进行,板状Na0.5Bi0.5TiO3颗粒裂解形成纳米纤维.所得的Na0.5Bi0.5TiO3纳米纤维分散性好,具有钙钛矿结构,直径为30~150 nm,长度为几个微米到十几个微米.     

Characterization of ternary (Na0.5K0.5)1?xLixNbO3 lead-free piezoelectric ceramics prepared by molten salt synthesis method

(Na_0.5K_0.5)_1−x Li _x NbO₃ powders and ceramics were prepared by molten salt synthesis method. Pure perovskite-phase powder was obtained at a low temperature of 740 °C with a grain size of below 800 nm. The effects of the LiNbO₃ on phase transition, microstructure, electrical properties, and temperature stability were investigated. A morphotropic phase boundary was identified. The scanning electron microscopy indicated that the (Na_0.5K_0.5)_1−x Li _x NbO₃ powders and ceramics obtained by the molten salt synthesis method have a relatively uniform particle size and microstructure. The results indicate that these materials are promising candidates for lead-free piezoelectric ceramics for practical applications.     

溶胶-凝胶法制备(Na0.85K0.15)0.5Bi0.5TiO3铁电薄膜晶化行为研究

利用溶胶-凝胶法在(111)Pt/Ti/SiO2/Si衬底上成功制备了无铅(Na0.85K0.15)0.5Bi0.5TiO3(NKBT)铁电薄膜。利用XRD和原子力显微镜(AFM)分别对薄膜的晶化行为和表面形貌进行了表征。结果表明,在一定温度范围内,随着热分解温度和退火温度的升高,薄膜的晶化程度变得越来越完全,晶粒变得更加均匀致密。当热分解温度为450℃、退火温度为700℃时,薄膜表现出最优的晶化行为,其铁电性能良好,剩余极化强度(Pr)和矫顽场强(Ec)分别为10.37μC/cm2和78.2kV/cm。     

Structure and electrical properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Bi0.5(Na0.82K0.18)0.5TiO3–BiAlO3 lead free piezoelectric ceramics

0.09(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–(0.01 − x) Bi_0.5(Na_0.82K_0.18)_0.5TiO₃–x BiAlO₃ (BNBKT–xBA) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction processes. Structure, ferroelectric and piezoelectric properties of BNBKT–xBA ceramics were investigated. X-ray diffraction data shows that BNBKT–xBA ceramics form the pure perovskite phases and the ceramics have the morphotropic phase boundary when x ≤ 0.030. At room temperature, the BNBKT–xBA ceramics at x = 0.030 have better electrical properties, the piezoelectric constant d₃₃ and planar coupling factor k_p of BNBKT–xBA ceramics reaches peak values at x = 0.030: d₃₃ = 217 pC N⁻¹, k_p = 0.308. The remnant polarization P_r, mechanical quality factor Q_m and relative dielectric constant ?_r of BNBKT–xBA ceramics at x = 0.030 attains 33.8 μC cm⁻², 133 and 928 (100 KHz), respectively. As BA content increase, the depolarization temperature T_d shift toward lower temperature, and T_d of BNBKT–xBA ceramics with x = 0.030 decreased to 55 °C.     

Electrical properties of (K0.5Na0.5)1? x Ag x NbO3 lead-free piezoelectric ceramics

(K_0.5Na_0.5)_1−x Ag _x NbO₃ lead-free piezoelectric ceramics have been fabricated by an ordinary ceramic technique. The results of XRD reveal that Ag⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a new solid solution with an orthorhombic perovskite structure and the solubility of Ag⁺ into A-sites of K_0.5Na_0.5NbO₃ is about 0.20. The ceramics can be well-sintered at 1,100–1,110 °C. The partial substitution of Ag⁺ for A-site ion (K_0.5Na_0.5)⁺ decreases slightly both paraelectric cubic-ferroelectric tetragonal (T _C) and ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperatures (T _O−T). The ferroelectricity of the ceramics becomes weak at high Ag⁺ concentration. The ceramic with x = 0.10 possesses optimum electrical properties: d ₃₃ = 135 pC/N, k _P = 0.43, k _t = 0.46, ε _r = 470, tanδ = 3.39%, and T _C = 394 °C.     

Correlation between the thermal expansion, isothermal compressibility, and photoconductivity of the (TlGaSe2)1 ? x(TlInS2)x (x = 0.1, 0.2) solid solutions

The thermal expansion coefficient, isothermal compressibility, and photoconductivity of the (TlGaSe₂)_0.9(TlInS₂)_0.1 and (TlGaSe₂)_0.8(TlInS₂)_0.2 solid solutions have been measured as a function of temperature. The measurement results have been used to evaluate the Debye characteristic temperature and band gap temperature coefficient of the solid solutions. It is shown that an increase in their thermal expansion coefficient is accompanied by a decrease in their band gap temperature coefficient.     

Dielectric and impedance spectroscopy of (CoNiO3)0.5–(BaTiO3)0.5 solid solution for device applications

The polycrystalline sample (CoNiO₃)_0.5(BaTiO₃)_0.5 has been successfully synthesized by conventional high-temperature solid state reaction route. The room temperature X-ray Diffraction (XRD) data conforms single phase new compound. The dielectric, impedance and transport behaviour of the sample has been analysed in detail. It is observed in the present study that the material possess high dielectric constant and low loss factor at room temperature may be suitable for microwave applications. The signatures of grain and grain boundary contribution have been noticed from impedance spectroscopy which confirms the presence of different types of charge.

     

Structure of Sr1 ? xPbxFeO3 ? δ (0 < x < 0.5) perovskite-like materials

We have synthesized Sr_{1 − x} Pb _x FeO_{3 − δ} (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5) perovskite-like materials and studied their structure by X-ray diffraction, M?ssbauer spectroscopy, and electron microscopy. According to the X-ray diffraction data, the Pb solubility limit in the perovskite structure is x ≈ 0.15. The materials with x = 0.05 and 0.1 contained Pb_1.33Sr_0.67Fe₂O₅ inclusions 10–30 nm in size. Using chronopotentiometry and temperature-programmed desorption, we have estimated oxygen mobility in the materials with x = 0.05 and 0.1. The results demonstrate that Pb doping increases oxygen mobility in the strontium-ferrite-based materials.     

Frequency effect on the electrical and dielectric properties of (TlGaS2) 1 ? x(TlInSe2)x (x = 0.005, 0.02) single crystals

The electrical properties (loss tangent (tanδ), real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity, and ac conductivity across the layers (σ_ac)) of (TlGaS₂)_{1 − x} (TlInSe₂) _x (x = 0.005, 0.02) layered single crystals have been studied in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. Almost throughout the frequency range studied, their ac conductivity follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level. The Fermi-level density of states (N _F ), the spread of their energies, the mean hop time τ and distance R, and the concentration of deep traps determining the ac conductivity of the crystals (N _t ) have been estimated. With increasing x in (TlGaS₂)_{1 − x} (TlInSe₂) _x , N _F and N _t increase, while τ and R decrease.     

Thermodynamic properties of (TeO2)0.95 ? n ? z(ZnO)z(Na2O)n(Bi2O3)0.05 glasses

The heat capacity (C _p ⁰) of the tellurite glasses

Production and dielectric properties of lead-free ceramics with the formula [(Na0.5K0.5)1 ? xLix](Nb1 ? y ? zTaySbz)O3

The influence of past history on the possibility of obtaining high-density ferroelectric ceramics of solid solutions [(Na_0.5K_0.5)_{1 − x} Li _x ](Nb_{1 − y − z} Ta _y Sb _z )O at x = 0–0.14, y = 0, 0.1, 0.2, and z = 0–0.1 is identified. The dynamics of behavior of materials under a field in the process of polarization is evaluated. The relative dielectric permeability of samples in a wide range of temperatures (20–700°C) and frequencies (25 Hz-1 MHz) of a variable electric field is studied. On the basis of study of dielectric, piezoelectric, and elastic properties of solid solutions, prospective objects for further technological elaboration and modification of chemical composition with the goal of improving the electrophysical parameters are selected. Original Russian Text ? I.A. Verbenko, O.N. Razumovskaya, L.A. Shilkina, L.A. Reznichenko, K.P. Andryushin, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 6, pp. 762–768.     

Nanoclustering in (Nd0.7Sr0.3)1 ? xMn1 + xO3 ± δ solid solutions

The structure of (Nd_0.7Sr_0.3)_{1 − x} Mn_{1 + x} O_{3 ± δ} solid solutions with x = 0–0.2 (Nd: Sr atomic ratio maintained constant at 2.33) annealed at temperatures from 1200 to 1500°C has been studied by X-ray diffraction. The results demonstrate that, as the annealing temperature is raised, the atomic order in the stoichiometric (x = 0) materials is stable to changes in the homogeneity of the solid solution. In the case of the nonstoichiometric manganites with x = 0.15–0.20, an increase in annealing temperature is accompanied by the development of chemical and topological ordering processes in the matrix structure and cluster growth. The cluster size ranges from 100 to 250 ?, and the largest percentage of clusters (3.5–5.5%) consist of the matrix phase. The fraction of clusters of binary composition, such as MnO-MnO₂, is 0.5–2.0%.     

Synthesis and characterization of nano-sized BaxSr1?xSO4 (0 ≤ x ≤ 1) solid solution by a simple surfactant-free aqueous solution route

A facile aqueous solution route has been employed to synthesize Ba _x Sr_1−x SO₄ (0 ≤ x ≤ 1) solid solution nanocrystals at room temperature without using any surfactants or templates. The as-synthesized products were characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), scanning electron microscopy (SEM), and differential scanning calorimetry-thermogravimetry (DSC-TG). The Ba _x Sr_1−x SO₄ solid solution nanocrystals exhibit an orthorhombic structure and an ellipsoidal-shaped morphology with an average size of 80–100 nm. The lattice parameters of Ba _x Sr_1−x SO₄ solid solution crystals increase with increasing x value. However, they are not strictly coincident with the Vegard’s law, which indicates that the as-obtained products are non-ideal solid solutions. The Ba _x Sr_1−x SO₄ solid solution nanocrystals have an excellent thermal stability from ambient temperature to 1300°C with a structural transition from orthorhombic to cubic phase at about 1111°C.     

Temperature dependence of ferroelectric and dielectric properties of textured 0.98(0.94Na0.5Bi0.5TiO3–0.06BaTiO3)–0.02K0.5Na0.5NbO3 thick film

Textured 0.98(0.94Na_0.5Bi_0.5TiO₃–0.06BaTiO₃)–0.02K_0.5Na_0.5NbO₃ thick film was prepared by reactive templated grain growth (RTGG) method. The effect of temperature on ferroelectric and dielectric behaviors of the thick film was investigated. Its dielectric constant as a function of temperature displayed typical relaxation behavior, which was similar to that of NBT-based bulk ceramics. Remnant polarization, saturation polarization, and coercive field of the thick film all decreased with increasing temperature. Dielectric constant and tunability of the film were also dependent on temperature. Electric field dependence of dielectric constant of the thick film suggested a transition from ferroelectric to antiferroelectric phase at around the depolarization temperature. A strong increase in leakage current density with increasing temperature was observed, which could be related to the enhanced activity of conductivity carriers.     

Self-propagating high-temperature synthesis of Y2O3 powders from Y(NO3)3x(CH3COO)3(1 ? x) · nH2O

We have studied the self-propagating high-temperature synthesis (SHS) of yttrium oxide from Y(NO₃)_3x (CH₃COO)_{3(1 − x)} · nH₂O (0.3 ≤ x ≤ 0.7) acetate nitrates, calculated their standard enthalpies of formation using the method of valence states of atoms in a chemical compound, and compared calculated and experimentally determined yttrium oxide SHS temperatures. Using thermogravimetry and differential scanning calorimetry data and thermodynamic analysis, we have determined the optimal range of yttrium acetate nitrate compositions for the SHS of Y₂O₃ powder.     

Ferroelectric and piezoelectric properties of [(Bi0.98La0.02Na1?xLix)0.5]0.94Ba0.06TiO3 lead-free ceramics

Lead-free ceramics [(Bi_0.98La_0.02Na_1−x Li _x )_0.5]_0.94Ba_0.06TiO₃ have been prepared by an ordinary sintering technique and their ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction reveal that Li⁺, Ba²⁺, and La³⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure. The partial substitution of Li⁺ lowers the coercive field E _c and improves the remanent polarization P _r. Because of the larger P _r and lower E _c, the ceramic with x = 0.10 exhibits optimum piezoelectric properties: d ₃₃ = 212 pC/N and k _P = 36.1%. The partial substitution of Li⁺ for Na⁺ shifts the depolarization temperature T _d toward low temperature. The ceramics exhibit relaxor characteristic, which is probably resulted from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics contain both the polar and non-polar regions near/above T _d, which cause the polarization hysteresis loop become deformed and the ceramics become depolarized.     

Cation mobility in Li1 + xTi2 ? xCrx(PO4)3 NASICON-type phosphates

Li_{1 + x} Ti_{2 − x} Cr _x (PO₄)₃ NASICON-type materials have been prepared and characterized by X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. The results demonstrate that Cr³⁺ doping increases the ionic conductivity of LiTi₂(PO₄)₃ within the single-phase region of the doped material, which extends to x = 0.7. From temperature-dependent ionic conductivity data, the activation energy for lithium transport through interstitial sites and the enthalpy of defect formation in LiTi₂(PO₄)₃ are estimated at 30.0 ± 0.5 and 56 ± 1 kJ/mol, respectively.