Dielectric and impedance spectroscopy of Sr(Bi0.5Ta0.5)O3 electroceramics

Polycrystalline sample of Sr(Bi_0.5Ta_0.5)O₃ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction analysis confirms the formation of single-phase compound of orthorhombic crystal structure at room temperature. The study of microstructure of gold-coated pellet by scanning electron microscopy shows well-defined and homogeneous distribution of grains on the surface of the sample. The dielectric properties of the compound studied in a wide frequency range (1 kHz–1 MHz) at different temperatures (27–500 °C), exhibits that they are temperature dependent. Detailed analysis of impedance spectra showed that the electric properties of the material are strongly dependent on frequency and temperature. Studies of electric modulus show the presence of hopping conduction mechanism in the material with non-exponential type of relaxation. The decrease in value of bulk resistance on increasing temperature suggests the negative temperature co-efficient of resistance behavior of the material. The AC-conductivity spectrum provides a typical-signature of an ionic conducting system, and is found to obey Jonscher’s universal power law.     

Tuning the microwave dielectric properties of La(Mg0.4Sr0.1Sn0.5)O3 by introducing Ca0.8Sr0.2TiO3

The influence of sintering temperature on the microwave dielectric properties and microstructure of the (1 ? y)La(Mg_0.4Sr_0.1Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramic system were investigated with a view to their application in microwave devices. The (1 ? y)La(Mg_0.4Sr_0.1Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramic systems were prepared using the conventional solid-state method. The X-ray diffraction patterns of the (1 ? y)La(Mg_0.4Sr_0.1Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramic system shifted to higher angle as y increased. A dielectric constant of 41.2, a quality factor (Q × f) of 56,900 GHz, and a temperature coefficient of resonant frequency of ?6 ppm/ °C were obtained when the 0.4La(Mg_0.4Sr_0.1Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system was sintered at 1,550 °C for 4 h.     

High dielectric constant ceramics in the PbSc0.5Ta0.5O3-PbZrO3 and PbSc0.5Ta0.5O3-PbTiO3 systems

The properties of (1-x) PbSc_0.5Ta_0.5O₃-(x) PbZrO₃ ceramics (0.075 <x < 0.2), have been investigated using three different mixed oxide preparation routes. These were (i) a single-stage calcination (at 900°C) between lead, scandium, tantalum and zirconium oxides, (ii) the reaction between single phase PbSc_0.5Ta_0.5O₃ and PbZrO₃ powders (also at 900°C), and (iii) the formation of zirconium-modified scandium tantalate (via a high-temperature prereaction stage) prior to calcination with lead oxide. It was found that this third preparation route results in transparent, 100% dense, single-phase perovskite ceramics which exhibit particularly sharp first-order ferroelectric to paraelectric phase transitions. Material with a maximum relative permittivity of 36 × 103 at 64°C, and a dielectric loss of 7.5 × 10^–4, was obtained for anx value of 0.125. Results are compared with those for ceramics in a similar range of compositions in the (1-x) PbSc_0.5Ta_0.5O₃-(x)PbTiO₃ system; these were prepared using only one of the above routes, and involved calcining PbSc_0.5Ta_0.5O₃ with PbTiO₃ powder.     

Effect of Sm substitution on microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of Nd_(1?x)Sm_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation in mobile communication. The Nd_(1?x)Sm_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_0.98Sm_0.02(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A density of 6.87 g/cm³, a dielectric constant (ε _r ) of 19.2, a quality factor (Q × f) of 104,300 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?57 ppm/°C were obtained for Nd_0.98Sm_0.02(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Improved microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramic with Ba2+ substitution

The microwave dielectric properties of La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for wireless communications. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics contained La₂Sn₂O₇. An apparent density of 6.54 g/cm³, a dielectric constant ( $ \varepsilon_{r} $ ε r ) of 20.1, a quality factor (Q  $ \times $ ×  f) of 51,600 GHz, and a temperature coefficient of resonant frequency ( $ \tau_{f} $ τ f ) of ?82 ppm/°C were obtained for La(Mg_0.43Ba_0.07Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Improved microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics with Ni2+ substituting

This study elucidates the microwave dielectric properties and microstructures of Nd(Mg_0.5?xNi_xSn_0.5)O₃ ceramics with a view to their potential for microwave devices. The Nd(Mg_0.5?xNi_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.43Ni_0.07Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant ( $ \varepsilon_{r} $ ) of 19.3 and a quality factor (Q × f) of 93,400 GHz and a temperature coefficient of resonant frequency ( $ \tau_{f} $ ) of ?66 ppm/ °C were obtained for Nd(Mg_0.43Ni_0.07Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Effect of nickel on microwave dielectric properties of Ba(Mg1/3Ta2/3)O3

The dielectric and physical properties of the complex perovskite Ba(Mg_1/3Ta_2/3)O₃ system in which magnesium was substituted for nickel from 0.03–0.67 mol%, were investigated in the temperature range 20–110C, and the frequency range 10.5–14.5 GHz. As the nickel content was increased, the dielectric constant, the degree of ordering, and the unloaded Q decreased. The temperature dependence of the dielectric constant and the temperature coefficient of resonant frequency of the specimens annealed at 1500C for 20 h were found to be greater than those of the specimens sintered at 1650C for 2 h. These results are due to the increase in the density, the increase in grain size, and the lattice distortion.     

Structural,transmittance, ferroelectric,energy storage,and electrical properties of K0.5Na0.5NbO3 ceramics regulated by Sr(Yb0.5Ta0.5)O3

Journal of Materials Science: Materials in Electronics - High transparent lead-free (1?x)K0.5Na0.5NbO3-xSr(Yb0.5Ta0.5)O3 (KNN-xSYbT, x = 0.005, 0.01, 0.02, 0.03, 0.04, 0.05) ferroelectric...     

Influence of Ba2+ substitution on the microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of Nd(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation in mobile communication. The Nd(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.47Ba_0.03Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A density of 6.91 g/cm³, a dielectric constant (ε _r ) of 19.14, a quality factor (Q × f) of 97,500 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?65.4 ppm/°C were obtained for Nd(Mg_0.47Ba_0.03Sn_0.5)O₃ ceramics that were sintered at 1,600 °C for 4 h.     

Sintering and dielectric properties of Sr(Bi2Ta2)0.95Ti0.2O9 ceramics

In this study, TiO₂ is used to substitute the Bi₂O₃ and Ta₂O₅ sites of the SrBi₂Ta₂O₉ ceramics to form Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ composition. From the X-ray patterns, the 2θ values shift to higher values as the sintering temperatures increase. At lower sintering temperatures of 1200–1250 °C, the Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ ceramics reveal a two-phase structure, bar-typed grains and disk-typed grains coexist; when 1300 °C is used as the sintering temperature, only the bar-typed grains are revealed. The sintering temperatures also have large influences on the maximum dielectric constants and the Curie temperatures of Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ ceramics.     

Structural and dielectric properties of La substituted polycrystalline Ca(Ti0.5Fe0.5)O3

Polycrystalline Ca_1?x La _x (Ti_0.5Fe_0.5)O₃ were prepared by the standard solid state reaction technique. Pellet shaped samples prepared from each composition were sintered at 1573 K for 5 h. The X-ray diffraction analysis indicated the formation of a single-phase orthorhombic structure. The lattice parameters as well as densities increased but the average grain sizes decreased with the increase of La content. The dielectric measurements were carried out at room temperature as a function of frequency and composition. The experimental results revealed that dielectric constant (?′) decreased but dielectric loss (tan δ) and ac electrical conductivity (σ _ac ) increased as frequency increased. The composition dependence of ?′ and tan δ indicated that they decreased with the increase of La content. The σ _ac was derived from the dielectric measurements and it is concluded that the conduction in the present samples is due to mixed polarons hopping.     

脉冲激光沉积Ba0.5Sr0.5TiO3、Pb0.5Ba0.5TiO3和Pb0.5Sr0.5TiO3薄膜及其介电性质

采用脉冲激光沉积法,在Pt／Ti／SiO2／Si基底上分剐制备厚度为350nm的Ba0.5Sr0.5TiO3(BST)、Pb0.5Ba0.5TiO3(PBT)和Pb0.5Sr0.5TiO3(PST)薄膜并研究了它们的介电性质。XRD显示,在相同的制备条件下三者具有不同的择优取向,PST具有(110)择优取向,PBT具有(111)择优取向,而BST则是混合取向。SEM显示三者样品表面均匀致密,颗粒尺寸大约在50nm至150nm之间。PST与BST、PBT相比有更高的介电常数,在频率为10kHz时,分别为874、334和355,而损耗都较低,分别为0．0378、0．0316和0．0423,同时PST漏电流也是最小的。测量薄膜的C-V特性扣铁电性能表明室温下BST呈现的是顺电相,PST和PBT则呈铁电相。本文也测量了薄膜在不同频率下的介电温度特性,BST、PBT和PST均表现出频率弥散现象,即随着频率的降低．居里温度降低而介电常数会升高。并测得BST和PST的居里温度分剐为-75和150℃。而PBT的居里温度在250℃以上。本文研究表明：与BST相比较,PBT的介电常数与之相近,漏电流较大;而PST具有高介电常数,较小的漏电流和较大的电容-电压调谐度,在相关半导体器件中的应用将有很大的潜力。     

Low-temperature sintering and microwave dielectric properties of CaTi1−x(Fe0.5Nb0.5)xO3 ceramics with B2O3 addition

CaTi_1−x(Fe_0.5Nb_0.5)_xO₃ (0 ≤ x ≤ 1) dielectrics were synthesized via the solid state reaction route and structure analysis was performed together with the dielectric characterization. The substitution of Ti⁴⁺ by Fe³⁺/Nb⁵⁺ and developed phase were studied by X-ray diffraction. The dielectric constant and temperature coefficient of resonant frequency decrease rapidly with an increase of x. The influence of 1–5 wt.% B₂O₃ as a sintering additive investigated at CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ solid solutions. The dielectric properties were found to strongly depend on the sintering conditions and contents of B₂O₃ additions. ɛ_r = 52.3, Q × f_o = 2930 GHz and T_f = 13 ppm/°C were obtained for CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ specimen 3 wt.% B₂O₃ sintered at 900 °C for 2 h.     

Surface morphology and dielectric properties of alkoxy-derived Sr2Ta2O7 and Sr2Ta, Nb2O7 thin films

Sr₂Ta₂O₇ and Sr₂(Ta, Nb)₂O₇ thin films were prepared from molecular structure-controled alkoxide solutions. The Sr₂Ta₂O₇ thin films initiated to crystallize at around 650 °C and showed random orientation. The surface topography developed was dependent on the solutions. In the thin films prepared from the ethanolic solution, grains formed at low temperatures. However, many small pores still remained and no grains were observed in the thin films prepared from the methoxyethanolic solution. In contrast, the 800 °C-annealed Sr₂(Ta, Nb)₂O₇ thin films showed the (0 k 0) orientation as in Sr₂Nb₂O₇ thin films. The dielectric constants and loss factors of the 750 °C-annealed Sr₂Ta₂O₇ and Sr₂(Ta_0.7Nb_0.3)₂O₇ thin films were around 90 and less than 0.05 at 100 kHz, respectively.     

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.     

钛酸锶钡纳米粉体的溶胶-凝胶自蔓延燃烧制备及其介电性能研究

采用溶胶-凝胶和自蔓延燃烧技术,制备了平均晶粒尺寸约20nm的Ba0.5Sr0.5TiO3(BST)纳米粉体.将纳米粉体压制成形后进行烧结,得到BST陶瓷.采用XRD、SEM、TEM和LCR数字电桥研究了BST的结构、形貌和介电性质.结果表明,干凝胶自蔓延燃烧后,可直接形成分散性好、颗粒尺寸均匀、具有钙钛矿结构的BST纳米粉体.BST陶瓷压片经1250℃烧结2h后获得了致密的结构和相对较大的介电常数.粉体的结晶温度和烧结体的烧结温度均低于传统工艺.很明显,溶胶-凝胶自蔓延燃烧法在纳米材料的制备方面具有明显的技术优势.