Dielectric Properties of Bi4−x La x Ti3O12 (0 ≤ x ≤ 2) Ceramics

The dielectric properties of the Bi_4–x La _x Ti₃O₁₂ (0 x 2) ceramics were characterized and discussed together with the P-E relation (polarization vs. electric field). With increasing x, the P-E relation changed from normal ferroelectric hysteresis loops to pure linear relation, which indicated that La³⁺ substitution for Bi³⁺ in Bi₄Ti₃O₁₂ induced a phase transition from ferroelectric to paraelectric state at ambient temperature. Low loss dielectric ceramics with temperature stable dielectric constant were obtained for x > 1.2 in Bi_4–x La _x Ti₃O₁₂ at 1 MHz. And the loss increased in all the compositions when the ceramics were measured at microwave frequencies.     

Preparation and Properties of Bi4 − x Nd x Ti3O12 Thin Films by Chemical Solution Deposition

Neodymium-modified Bi₄Ti₃O₁₂, (Bi, Nd)₄Ti₃O₁₂ (BNT) ferroelectric thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates using metal-organic precursor solutions by the chemical solution deposition method. The BNT precursor films crystallized into the Bi layered perovskite Bi₄Ti₃O₁₂ (BIT) as a single-phase above 600C. The synthesized BNT films revealed a random orientation having a strong 117 reflection, whereas non-substituted BIT thin films exhibited a random orientation with strong 00l diffractions. Among Bi_{4 – x}Nd_xTi₃O₁₂ [x = 0.0, 0.5, 0.75, 1.0] thin films, Bi_3.25Nd_0.75Ti₃O₁₂ thin films showed a well-saturated P-E hysteresis loop with the highest P_r (22 C/cm²) and a low E_c (69 kV/cm) at an applied voltage of 5 V. The Nd-substitution with the optimum amount for the Bi site in the BIT structure was effective not only for promoting the 117 preferred orientation but also for improving the microstructure and ferroelectric properties of the resultant films.     

Scaling Effect on the Dielectric Constant in Ba(Ti x Zr1−x )O3 Thin Films

Recent work on PZT and BST thin films reveal a thickness dependence of the dielectric constant for a film thickness below 100 nm. This effect is commonly attributed to an interfacial layer between the electrode and the dielectric film (dead layer). In this contribution we report on the influence of the film thickness on the dielectric constant of Ba(Ti_xZr_{1 – x})O₃ thin films with different Zr-contents (x = 0–30 at.%). The films were prepared by chemical solution deposition (CSD) with thickness between 30 and 350 nm.The electrical characterization was performed in a temperature range between 25 and 200C. Results were interpreted with respect to the formation of a serial dead layer capacitance.     

Temperature-Stable High-ε Dielectrics Ceramics Based on (1 − x) Ba5NdTi3Ta7O30/xBi4Ti3O12

Modification of Ba₅NdTi₃Ta₇O₃₀ dielectric ceramics was investigated through introducing Bi₄Ti₃O₁₂. With increasing of Bi₄Ti₃O₁₂ content, the dielectric constant increased, and the temperature coefficient of the dielectric constant changed from negative to positive. The small temperature coefficient ( < 50 ppm/°C) combined with high dielectric constant ( = 178) and low dielectric loss (tan = 0.007 at 1 MHz) was achieved in the composition x = 0.6.     

Raman Scattering Study of the Pb(Hf x Ti1−x )O3 Ceramics

Raman spectroscopy was used to study the long wavelength vibrations of tetragonal perovskite (space group P4mm) Pb(Hf_xTi_1–x)O₃ (PHT) (0.10 x 0.50) samples at room temperature and at 20 K. For x 0.40, Raman spectra collected from the PHT samples were very similar to the previous spectra collected from the PZT samples with the same value of x, except the mode at around 190 cm^–1, whose frequency was decreasing with increasing x in PHT ceramics. Correspondingly, the latter feature was taken as a sign of the mass effect (Hf versus Zr) while the similarity of the remaining parts of the Raman spectra was assumed to be due to the almost identical ionic radii difference between Ti⁴⁺ and Zr⁴⁺ and between Ti⁴⁺ and Hf⁴⁺ ionic radii. The behaviour of the mode at around 280 cm^–1 revealed that a phase transition occurred once x was changing from 0.40 to 0.50.     

Microstructural and Electrical Properties of (Ba x Sr 1 − x )Ti 1 + y O 3 + z Thin Films Prepared by RF Magnetron Sputtering

The electrical and microstructural properties of (Ba x Sr 1 m x )Ti 1+y O 3+z (BST) thin films prepared by RF magnetron sputtering were investigated as a function of deposition temperature over the range of 100 C to 650 C. Films deposited above approximately 350 C on Pt/TiO 2 /SiO 2 /Si substrates were polycrystalline with relative permittivites of 100 nm thick BST thin films varying from 100 at 350 C to 600 at 650 C. For deposition temperatures below approximately 350 C, the electrical properties were strongly influenced by the presence of a less crystalline BST layer. Films deposited at 250 C were comprised of a multilayer polycrystalline/less crystalline BST structure. The less crystalline BST layer strongly affected both measured dielectric permittivity and leakage properties. Leakage characteristics of Pt/BST(250C)/Pt capacitors exhibited a power law dependence on voltage or an exponential dependence on square root of the applied voltage depending on whether the top Pt electrode adjacent ot the polycrystalline BST layer was biased at a high or low electric potential, respectively. Mechanisms for the observed leakage behavior are discussed.     

Synthesis and Dielectric Characterization of Pyrochlore-Free Pb1−x Ba x (Zn1/3Nb2/3)O3 Ceramics

The dielectric properties and synthesis of pyrochlore-free lead zinc niobate ceramics with Ba substituting for Pb were investigated. Ba partial substitution for Pb was effective in stabilizing the perovskite structure in PZN ceramics, where the minimum amount of Ba substitution needed was about 20 mol%. The dielectric loss and the temperature coefficient of dielectric constant of PZN were reduced markedly with Ba substitution, while the dielectric constant was greater than 110. Good dielectric properties were obtained for the composition of Pb_0.3Ba_0.7(Zn_1/3Nb_2/3)O₃: = 133.5, tan = 0.0009, = –811 ppm/°C.     

Investigation of dielectric and relaxor ferroelectric properties in Ba(Zr x Ti1−x )O3 ceramics

Barium zirconate titanate Ba(Zr _x Ti_1?x )O₃ (BZT x?=?0.1, 0.15, 0.2, 0.25) ceramics doped with Nb₂O₅ have been prepared by a traditional solid phase reaction. The temperature dependence of dielectric permittivity has been investigated. The results show that the phase transition temperature T _c is depressed and the diffuse phase transition behavior is enhanced with increasing Zr content. The Cole–Cole plot has been discussed and the cause of the deviation has been analyzed. The temperature dependence of inverse dielectric constants was investigated. A modified Curie–Weiss law can be used to describe the diffuseness of a phase transition, and diffusion factor increases with the Zr content.     

Piezoelectric and Dielectric Properties of Pb(Zr x Ti1 − x )O3-Pb(Ni1/3Sb1/3Nb1/3)O3 Piezoelectric Ceramics

In this paper, piezoelectric and dielectric properties of 0.9PbZr_xTi_1–xO₃-0.1PbNi_1/3Sb_1/3Nb_1/3O₃ were studied as a function of Zr/Ti mole ratio(x) for application to piezoelectric actuator. Also, microstructure and crystalline phase are investigated by using SEM and XRD, respectively. As a results, the substitution of Sb5+ to B-site increases the piezoelectric and dielectric properties, and when Zr/Ti mole ratio is 49/51 and ternary mole ration is 0.1(0.9PbZr_0.49Ti_0.51O₃-0.1PbNi_1/3Sb_1/3Nb_1/3O₃), the corresponding composition were found belonging to the Morphotropic Phase Boundary region with electromechanical coupling coefficient(k_p), mechanical quality factor (Q_m), permittivity(_r) and piezoelectric strain constant(d₃₃) equaled to 63%, 360, 2000 and 470 pC/N, respectively. Sintering temperature was about 1150_C and Curie temperature was determined around 290_C.     

Ferroelectric Bi4Ti3O12 and Bi4−x La x Ti3O12 ceramics prepared by a new sol-gel route

Ceramics of bismuth titanate, Bi₄Ti₃O₁₂ (BIT) and the La-doped series, Bi_4?x La _x Ti₃O₁₂ (xBLT) with x?=?0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.75, have been synthesized by a new sol-gel process based on ethylene glycol. La-doping is found to reduce the temperature of the formation of pure Bi-layer-structured phase from 600 °C in BIT and low La-doped xBLT (x?=?0.1–0.3) to 500 °C in high La-doped xBLT (x?=?0.4–0.75). Increasing the La-content in the xBLT ceramics decreases the contribution of the space charge polarization to the apparent dielectric permittivity. The ceramics of xBLT prepared by this sol-gel route exhibit improved dielectric properties, with a higher room temperature dielectric constant and lower losses up to high temperatures.     

Low Loss Tungsten-Based Electrode Technology for Microwave Frequency BST Varactors

The electrical properties of BaO-Nd₂O₃-Sm₂O₃-TiO₂ ceramics doped with low loss glass or low melting point oxide B₂O₃ are evaluated by impedance spectroscopy. Glass or B₂O₃ is doped as liquid phase sintering aid. Doping of glass/B₂O₃ enhances both the growth in the longitudinal direction of the columnar crystal and the preferred orientation of (002). The grain size increases and grain boundary decreases with the increase of dopant. Both the grain and grain-boundary resistivities decrease with the increase of dopant. The grain boundary activation energy for charge transport is larger than that of the grain activation energy. Possible mechanisms for the electrical behavior of the liquid-phase sintered BaO-Nd₂O₃-Sm₂O₃-TiO₂ ceramics are proposed and discussed.     

Effects of Glass Phase Additions and Stoichiometry on the Ba(Zn<Subscript>1/3</Subscript>X<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> (<Emphasis Type="Italic">X</Emphasis> = Ta or Nb) Sinterability and Dielectric Properties

Ba(Zn_1/3X_2/3)O₃ materials where X = Ta or Nb (respectively named BZT and BZN) exhibit attractive properties suitable for applications in type I Multi Layer Ceramics Capacitors (MLCC). Nevertheless, to produce such components using Base Metal Electrodes such as copper, a significant reduction of their sintering temperature is required. The aim of this work is first to study the effects of glass phases additions and secondly the stoichiometry influence on the sintering temperature of BZT and BZN. It is shown for example, that our materials can be sintered in air at a temperature lowered by 450C when sintering agents (B₂O₃ with LiF) are combined with a slight non-stoichiometry. The sintered samples are characterised in terms of final density, microstructure and phase content and it was underlined that such modifications (additions and stoichiometry) does not affect the dielectric properties.     

BCB对CSLLT陶瓷的烧结及介电性能的影响

在CaO-SrO-Li2O-Sm2O3-Nd2O3-TiO2(简称CSLLT)陶瓷中加入BaCu(B2O5)(简称BCB),研究了BCB对CSLLT陶瓷的烧结特性和介电性能的影响。结果表明:随BCB的添加,CSLLT陶瓷的烧结温度逐渐下降,并且具有高介电常数。其中,添加10?B后的CSLLT陶瓷其烧结温度从1 300℃显著下降到1 050℃,且在微波频率下具有如下介电性能:ε=77.3、Qf=4 735 GHz;τf=-48.1×10-6/℃(1 MHz)。     

SrLnAlO4 (Ln=Nd and Sm) Microwave Dielectric Ceramics

SrLnAlO₄ (Ln=Nd and Sm) ceramics with K₂NiF₄ structure were prepared by a solid state reaction approach, and their microwave dielectric characteristics were evaluated together with the microstructures. The single phase dense SrNdAlO₄ and SrSmAlO₄ ceramics were obtained by sintering at 1450–1475°C and 1475–1500°C, respectively, and the good microwave dielectric characteristics were achieved: (1) = 17.8, Q · f = 25,700 GHz, _f = –9 ppm/°C for SrNdAlO₄; and (2) = 18.8, Q · f = 54,880 GHz, _f = 2 ppm/°C for SrSmAlO₄ dense ceramics. The Qf value significantly increased with increasing sintering temperature.     

Ferroelectric Properties of the La0.03Sr0.225Ba0.7Nb2–yTiyO6–y/2 Ceramic System

The study of the dielectric properties of the stoichiometric Titanium doped Sr_0.255La_0.03Ba_0.7Nb₂O₆ ceramics prepared according to the formula Sr_0.225La_0.03Ba_0.7Nb_2–yTi_yO_6–y/2 is reported. A single phase compound is observed for low Ti content (y<0.1) in the XRD spectra, being isostructural with the SBN phase. For high Ti concentrations (y<0.1), the XRD patterns show, besides the SBN phase reflections, several small peaks associated with an additional phase present in the ceramics. A possible liquid phase sintering is analyzed. Strongly broadened dielectric curves are obtained in dielectric measurements, where the transition temperature decreases with the Titanium content. The diffuse phase transition coefficients are calculated, corroborating that Titanium increases the diffuse character of the transition in the monophasic region.     

Al2O3对Nb掺杂PTCR陶瓷材料的影响

研究了添加不同质量分数Al2O3的掺杂Nb的BaTiO3陶瓷材料。测量了烧结条件为1 300~1 350℃的陶瓷材料试样的室温电阻、R_T曲线、电阻温度系数及开关温度。在实验的基础上,分析讨论了不同含量的非晶态Al2O3与α_Al2O3对PTCR陶瓷电特性的影响。结果表明,随着Al2O3添加量的增加,材料的烧结温度降低,晶粒均匀,但材料的电特性变弱。     

微波烧结La掺杂CaCu3Ti4O12陶瓷的结构、介电和压敏性能

采用微波快速烧结法制备了La掺杂CaCu3Ti4O12致密陶瓷,研究了其结构、介电和压敏性能。所有Ca1-3x/2LaxCu3Ti4O12陶瓷均形成了CCTO晶相,但是La含量低于0.10时存在CuO第二相。随着La含量增加,Ca1-3x/2LaxCu3Ti4O12陶瓷介电常数随频率和温度变化越来越小;压敏电压逐渐增大,非线性系数也明显改善。其中La含量x=0.15时,Ca1-3x/2LaxCu3Ti4O12陶瓷具有良好的压敏性能:压敏电场强度为5.25 kV/cm,非线性系数为26.3。     

Processing and Electrical Properties of 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 Ceramics

Pb(Yb_1/2Nb_1/2)O₃-PbTiO₃ ceramics at the morphotropic phase boundary (50:50) were sintered by conventional and reactive methods to 95% theoretical density and grain sizes <10 m. Excess PbO, added to enhance the densification, resulted in PbO-based non-ferroelectric phases that degraded the electrical properties. Volatilization of excess PbO by annealing the samples after sintering resulted in dense, perovskite samples and excellent electrical properties. The best electrical properties, obtained via reactive sintering, were a remanent polarization, P _r, of 0.36 C/m², a maximum dielectric constant of 31,000 (at the T _c = 371°C and 1 kHz), a piezoelectric charge coefficient, d ₃₃, of 508 pC/N, and an electromechanical coupling coefficient, k ₃₃, of 0.61.     

Development of Translucent Aluminum Nitride (AIN) Using Microwave Sintering Process

Pure aluminum nitride (AIN) has been successfully sintered to highly translucent form by microwave sintering at 1850°C with a dwelling time of 30–60 minutes. The results showed that the sintering temperature should be at least 1850°C or higher to get reasonable translucency in the AIN sample by the microwave sintering process. On the other hand, the conventional sintering method requires much longer sintering time to obtain a translucent AIN ceramics.     

新型钨青铜型高介微波陶瓷的研究进展

随着现代移动通信的飞速发展,高介电常数微波介质陶瓷得到了极大的发展,并广泛应用于微波谐振器、滤波器、介质基板、移相器等微波元器件。本文综述了高介微波陶瓷之一的新型钨青铜型高介微波陶瓷近几十年来的研究进展,并展望了其发展趋势。