Dielectric properties of Ba0.6Sr0.4TiO3-Sr(Ga0.5Ta0.5)O3 solid solutions

Ba_0.6Sr_0.4TiO₃-Sr(Ga_0.5Ta,sub>0.5)O₃ solid solutions are prepared by a solid-state reaction method, and their dielectric and tunable characteristics are investigated. The solid solutions with cubic perovskite structures are obtained for compositions of 10-50 mol% Sr(Ga_0.5Ta_0.5)O₃. It is observed that the addition of Sr(Ga_0.5Ta_0.5)O₃ into Ba_0.6Sr,sub>0.4TiO₃ causes a shift in the phase transition peak to a lower temperature. Ba_0.6Sr_0.4TiO₃-Sr(Ga_0.5Ta,sub>0.5)O₃ solid solutions exhibit depressed and broadened phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. With the increase of Sr(Ga_0.5Ta_0.5)O₃ content, the dielectric constant, loss tangent, and tunability are decreased. 0.9Ba_0.6Sr_0.4TiO₃-0.1Sr(Ga_0.5Ta,sub>0.5)O₃ has a dielectric constant ϵ = 534 and a tunability of 16% at 100 kHz under 2.63 kV/mm. The dielectric characteristics of Ba_0.6Sr_0.4TiO₃-Sr(Ga_0.5Ta,sub>0.5)O₃ ceramics at microwave frequencies are also evaluated.     

Application of on-wafer TRL calibration on the measurement ofmicrowave properties of Ba0.5Sr0.5TiO3films

A series of Al/Ba_0.5Sr_0.5TiO₃ (BST) /sapphire multi-layered coplanar waveguide (CPW) transmission lines of different geometries and thin-film configurations was fabricated. We employed an accurate on-wafer Through-Line-Reflect (TRL) calibration technique and quasi-TEM analysis to measure the dielectric constant, loss tangent, and tunability of BST thin films using this CPW structure. Experimental results show that the overall insertion loss is less than 3 dB/cm even at frequencies as high as 20 GHz, which is the lowest obtained to date for metal/BST CPW devices. This result indicates that, with optimized impedance matching, normal conductors are also possibly suitable for fabricating low-loss tunable phase-shifter devices     

Structure and ferroelectric properties of Bi(Zn1/2Ti1/2)O3-(Bi1/2K1/2)TiO3 perovskite solid solutions

Lead-free piezoelectric ceramics based on χBi(Zn_1/2Ti_1/2)O₃-(1-χ)(Bi_1/2K_1/2)TiO₃ were obtained via solid state processing techniques. A single perovskite phase with tetragonal symmetry was obtained for Bi(Zn_1/2Ti_1/2)O₃ (BZT) substitutions up to 20 mol%. The maximum density was 97.1% at the composition of χ = 0.1. The dielectric measurement indicated that the transition temperature decreased linearly with increasing BZT content. The P-E loops revealed an increase in remanent polarization (P_r) with the addition of BZT. The maximum planar coupling coefficient, κ_r, for the χ = 0.1 composition was 21.6 and the piezoelectric coefficient, d₃₃, for χ = 0, χ = 0.05, and χ = 0.1 was 108, 185, and 235 pm/V, respectively. Overall, the dielectric and piezoelectric properties showed significant improvement when BZT was added.     

Reaction between the tetragonal tungsten bronze niobate K2Sr4Nb10O30 and the perovskite Pb(Mg1/3Nb2/3)O3

The search for dielectric materials with a high dielectric constant and ′_r = ƒ(T) curves with a flat profile fitting the X7R specification is still ongoing. Promising results were obtained by mixing compounds with closely related structures, such as the tetragonal tungsten bronze (TTB) niobate K₂Sr₄Nb₁₀O₃₀ and the perovskite Pb(Mg_1/3Nb_2/3)O₃ (PMN). The present study, based on three methods of synthesis, explores the origin of the spreading out of the dielectric curves ′_r = ƒ(T). For the composition 10x K_0.2Sr_0.4NbO₃ (KSN) + (1 − x)Pb(Mg_1/3Nb_2/3)O₃ (PMN) with x = 0.3–0.6, the three synthesis methods provided similar characteristics and for the highest perovskite ratio (x = 0.3), the ′_r = ƒ(T) curve exhibits a flat profile. When lithium is used as a sintering agent, ′_r = ƒ(T) curves present a linear dependency with the temperature. These materials are also characterized by a structural and a microstructural inhomogeneity. Two phases TTB and perovskite type, different from KSN and PMN, are present after calcination and sintering, but not evenly distributed. The PbO loss during sintering also contributes to the evolution of the properties of the material.     

微波可调BaSrZnSi2O7-Ba0.5Sr0.5TiO3复合陶瓷的结构与介电性能关系

采用传统电子陶瓷工艺制备出BaSrZnSi₂O₇-Ba_0.5Sr_0.5TiO₃复合陶瓷,系统研究了其相结构、微观结构和介电性能。研究表明：随着BaSrZnSi₂O₇的加入,样品的居里峰向低温方向移动;但BaSrZnSi₂O₇加入量达到一定程度后,居里峰在一定的温度下保持稳定。调制特性变化规律类似于居里峰的移动。品质因数（Q值）的变化主要取决于微波材料加入后的"掺杂"和"复合"效果。当BaSrZnSi₂O₇质量分数为60wt% 时,复合材料表现出良好的综合特性：介电可调率为 16%（10 kHz）,介电常数为152,Q值达到417（2.720 GHz）,表明BaSrZnSi₂O₇-Ba_0.5Sr_0.5TiO₃复合陶瓷是电可调微波器件很好的潜在应用材料。     

Characterisation of proton irradiated Ba0.65Sr0.35TiO3/P(VDF-TrFE) ceramic–polymer composites

Barium strontium titanate/poly (vinylidene fluoride-trifluoroethylene)70/30 (Ba_0.65Sr_0.35TiO₃/P(VDF-TrFE) 70/30) composite with high dielectric permittivity was developed by integrating high dielectric permittivity ceramic powder with proton irradiated polymer matrix. The composite after irradiation behaves as a relaxor ferroelectric material and this behaviour is similar to that of irradiated P(VDF-TrFE) 70/30 co-polymer. Due to the irradiation, dielectric peaks broadened and moved towards the lower temperature, creating high relative permittivity values in a broad temperature range. Ba_0.65Sr_0.35TiO₃/P(VDF-TrFE) composite with 0.5 ceramic volume fraction with a dosage of 80 Mrad can reach a relative permittivity of 160 at room temperature (at 1 kHz), which is about 14 times higher than that of pure copolymer. Polarization-electric field hysteresis loops of composites are strongly depended on the ceramic powder volume fraction and the effects of irradiation is less apparent in composites with higher ceramic powder volume fraction.     

The Dielectric Properties of Ba/sub 0.6S/r/sub 0.4/Cr/sub x/Ti/sub 1-x/O/sub 3/Thin Films Prepared by Pulsed Laser Deposition

Ba_0.6Sr_0.4Cr_xTi_1-xO₃ (BSCT) films were prepared by pulsed laser deposition with the value of x varying from 0 mol% to 2.0 mol%. X-ray diffraction analysis detected an increase in the lattice parameters, which could be due to the characteristics of the growth process. Dielectric properties and tunability of the BSCT films were measured. The dissipation factors of the films decreased with increasing Cr-concentration. The highest figure of merit (FOM) value of 33.3 was obtained in 1.0 mol%-doped BSCT film. As a result, the effect of Cr doping is positive.     

Structure and electrical properties of (100)-oriented Pb(Zn1/3Nb2/3)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films on La0.7Sr0.3MnO3 electrode by chemical solution deposition

(100)-oriented 0.462Pb(Zn_1/3Nb_2/3)O₃–0.308Pb(Mg_1/3Nb_2/3)O₃–0.23PbTiO₃ (PZN-PMN-PT) perovskite ferroelectric thin films were prepared on La_0.7Sr_0.3MnO₃/LaAlO₃ (LSMO/LAO) substrate via a chemical solution deposition route. The perovskite LSMO electrode was found to effectively suppress the pyrochlore phase while promote the growth of the perovskite phase in the PZN-PMN-PT film. The film annealed at 700 °C exhibited a high dielectric constant of 2130 at 1 kHz, a remnant polarization, 2P_r, of 29.8 μC/cm², and a low leakage current density of 7.2 × 10^− 7 A/cm² at an applied field of 200 kV/cm. The ferroelectric polarization was fatigue-free at least up to 10¹⁰ cycles. Piezoelectric coefficient, d₃₃, of 48 pm/V was also demonstrated. The results showed that much superior properties could be achieved with the PZN-PMN-PT thin films on the solution derived LSMO electrode than on Pt electrode by sputtering.     

Dielectric characteristics of barium strontium titanate films prepared by aerosol deposition on a Cu substrate

Polycrystalline barium strontium titanate (Ba_xSr_1-xTiO₃, BST) films were directly prepared on copper substrates using an aerosol deposition method (ADM) at room temperature. Electric properties, such as the dielectric constant and tunability, were investigated as a function of the Ba content in Ba_xSr_1-xTiO₃ (x = 1.0, 0.6, 0.4) films. At a frequency of 100 kHz, the dielectric constant of the as-deposited BST films were 100, 201, and 72 for x = 1.0, 0.6, and 0.4, respectively. After annealing in N₂ at 500degC, the dielectric constant of the films on Cu electrodes were 190, 400, and 170 at x = 1.0, 0.6, and 0.4, respectively. Moreover, the BST (x = 0.6) film showed a high tunability of 30% under an applied electric field of 300 kV cm^-1.     

Microwave dielectric properties of W-doped Ba0.6Sr0.4TiO3 thin films grown on (001) MgO by pulsed laser deposition with a variable oxygen deposition pressure

The microwave dielectric properties of Ba_0.6Sr_0.4TiO₃ 1 mol% W-doped thin films deposited using pulsed laser deposition, are improved by a novel oxygen deposition profile. The thin films were deposited onto (001) MgO substrates at a temperature of 720 °C. A comparison is made between three different oxygen ambient growth conditions. These include growth at a single oxygen pressure (6.7 Pa) and growth at two oxygen pressures, one low (6.7 Pa) and one high (46.7 Pa). Films were deposited in a sequence that includes both a low to high and a high to low transition in the oxygen deposition pressure. Following deposition, all films were post-annealed in 1 atm of oxygen at 1000 °C for 6 h. The dielectric Q (defined as 1 / tanδ) and the dielectric constant, ε_r, were measured at room temperature, at 2 GHz, using gap capacitors fabricated on top of the dielectric films. The percent dielectric tuning (defined as (ε_r(0 V) − ε_r(40 V)) / ε_r(0 V) × 100) and figure of merit (FOM) (defined as percent dielectric tuning × Q(0 V)) were calculated. The film deposited using the two-stage growth conditions, 6.7 / 46.7 Pa oxygen, showed a maximum Q(0 V) value with high percent dielectric tuning and gave rise to a microwave FOM twice as large as the single stage growth condition. The improved dielectric properties are due to initial formation of a film with reduced interfacial strain, due to the formation of defects at the film/ substrate interface resulting in a high Q(0 V) value, followed by the reduction of oxygen vacancies which increases the dielectric constant and tuning.     

Piezoelectric properties in (K0.5Bi0.5)TiO 3-(Na0.5Bi0.5)TiO3-BaTiO 3 lead-free ceramics

Lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB) x(Na_0.5Bi_0.5)TiO _3-y(K_0.5Bi_0.5)TiO₃-zBaTiO ₃ [x + y + z = 1; y:z = 2:1] were synthesized using conventional, solid-state processing. Dielectric maximum temperatures of 280degC and 262degC were found for tetragonal 0.79(Na_0.5Bi_0.5)TiO₃-0.14(K_0.5 Bi_0.5)TiO₃-0.07BaTiO$ d3 (BNBK79) and MPB composition 0.88(Na_0.5Bi_0.5)TiO₃-0.08(K _0.5Bi_0.5)TiO₃-0.04BaTiO$ d3 (BNBK88), with depolarization temperatures of 224degC and 162degC, respectively. Piezoelectric coefficients d₃₃ were found to be 135 pC/N and 170 pC/N for BNBK79 and BNBK88, and the piezoelectric d₃₁ was determined to be -37 pC/N and -51 pC/N, demonstrating strong anisotropy. Coercive field values were found to be 37 kV/cm and 29 kV/cm for BNBK79 and BNBK88, respectively. The remanent polarization of BNBK88 (~40 muC/cm²) was larger than that of BNBK79 (~29 muC/cm²). The piezoelectric, electromechanical, and high-field strain behaviors also were studied as a function of temperature and discussed     

Synthesis and humidity sensitive properties of nanocrystalline Ba1−xSrxTiO3 thick films

Nanocrystalline Ba_1−xSr_xTiO₃ (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) precursors were synthesized using the stearic acid gel method. After the precursors had been calcined at 600–950°C for 0.5–1 h, nanocrystalline powders with the cubic perovskite structure were obtained and these were made into thick films. The powder samples were characterized by differential thermal analysis, X-ray diffraction and transmission electron microscopy, and the thick film samples were characterized by scanning electron microscopy and X-ray diffraction. The humidity-sensitive properties of the nanocrystalline Ba_1−xSr_xTiO₃ thick films were investigated. The results show that these nanocrystalline thick films possess higher humidity sensitivity and lower resistance than those of conventional materials.     

Microwave dielectric characteristics of Ba(Mg1/3Ta2/3)O3 ceramics sintered at low-temperatures

The microwave dielectric properties and microstructures of Ba(Mg_1/3Ta_2/3)O₃ (BMT) ceramics sintered at low temperatures with 2–3 wt.% NaF additives were investigated. BMT ceramics sintered at 1340 °C for 3–12 h showed dielectric constants (_r) of 25.5–25.7, Qf values of 41 500–50 400 GHz and temperature coefficients of the resonator frequency (τ_f) of 10.9–21.4 ppm °C⁻¹. The variation of sintering time almost had no effect on the dielectric constant. The Qf value increased and the τ_f decreased with increasing sintering time. The ordering degree of Mg²⁺ and Ta⁵⁺ at B-sites increased with increasing sintering time.     

Effect of CeO2 addition on structure and electrical properties of (Na0.5Bi0.5)0.93Ba0.07TiO3 ceramics prepared by citric method

(Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃ ceramics added with 0–0.8 wt.% CeO₂ were prepared by a citrate method, and the influence of the CeO₂ addition on the structure and electrical properties was investigated. The specimens containing various amounts of CeO₂ show the coexistence of rhombohedral and tetragonal phases, with the relative content of the tetragonal phases gradually enhancing with increasing amount of CeO₂. Compared with (Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃, the specimen added with a small amount of CeO₂ (≤0.2 wt.%) display a slightly improved electromechanical coupling factor (k_p) and piezoelectric constant (d₃₃) in conjunction with a reduced dielectric loss (tg δ) and an enhanced mechanical quality factor (Q_m), while higher CeO₂ amounts led to a rapid deterioration of the piezoelectric and ferroelectric properties. The variation of the electrical properties with the CeO₂ addition was tentatively interpreted with respect to doping effect, crystal-structural evolution and stability of ferroelectric domains.     

Conduction analysis of Li2O doped 0.2[Pb(Mg1/3Nb2/3)]–0.8[PbTiO3–PbZrO3] ceramics fabricated by columbite precursor method

We have fabricated 0.2Pb(Mg_1/3Nb_2/3)O₃–0.8Pb(Zr_0.475Ti_0.525)O₃ [PMN–PZT] ceramics doped with various amounts of Li₂O (0, 0.05, 0.1, 0.2, 0.3 wt.%) using the columbite precursor method. The effects of Li-doping on the conduction behavior of PMN–PZT ceramics are discussed in relation to the low frequency dielectric dispersion and frequency domain measurement. The Li-doped PMN–PZT ceramics sintered at 950 °C showed a sufficient densification with large dielectric constant and low dielectric loss. The incorporation of Li⁺ ion in PMN–PZT ceramics led to an appreciable reduction in electrical conductivity and further enhanced the ferroelectric and piezoelectric properties. The activation energies of PMN–PZT + xLi₂O (x = 0, 0.05, 0.1, 0.2, 0.3 wt.%) ceramics calculated from ac conductivity measurement using the Arrhenius relation were 1.05, 1.25, 1.27, 1.38 and 1.41 eV, respectively. The conduction behavior is examined in the low frequency and high temperature region and the results are discussed in detail through crystal defect mechanism.     

Dielectric Investigations of 0.945(Bi0.5Na0.5) TiO3-0.055BaTiO3

Dielectric properties of 0.945(Bi_0.5Na_0.5) TiO₃-0.055BaTiO₃(BNBT5.5) (a composition close to the rhombohedral- tetragonal morphotropic phase boundary) ceramics are studied. It is shown that BNBT5.5 is a relaxor with a characteristic relaxation time that follows Vogel-Fulcher's law. The following Vogel-Fulcher parameters of the relaxation time were calculated: pi0 = (2.0 plusmn 2.4)middot10^-14 s, E/^kB = (1620 plusmn 270) K, T₀ = (262 plusmn 9) K.     

Effect of MnO addition on structure and electrical properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics prepared by citrate method

(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ ceramics added with 0–0.8 wt.% MnO were prepared by a citrate method, and the influence of the MnO addition on the structure and electrical properties was investigated. The results indicate that the addition of small amounts of MnO did not cause a remarkable change in crystal structure, but resulted in an evident evolution in microstructure. The dielectric constant (_r) and piezoelectric constant (d₃₃) significantly decrease with increasing MnO content, while the electromechanical coupling factor (k_p) presents a slight variation in the range of 0.25–0.28. The dissipation factor (tan δ) and mechanical quality factor (Q_m) attain a minimum value of 1.5% and a maximum value of 304 when adding 0.4 and 0.5 wt.% MnO, respectively. This research demonstrates that doping effect and microstructural evolution contribute cooperatively to the electrical properties of the ceramics.     

Influence of A-site nonstoichiometry on sintering, microstructure and electrical properties of (Bi0.5Na0.5)TiO3 ceramics

Lead-free (Bi_0.5Na_0.5)_1+xTiO₃ ceramics (x = −0.02, −0.01, −0.005, 0, 0.005 and 0.01) were prepared by ordinary sintering. The effect of A-site stoichiometry on the densification, microstructure, dielectric properties, high-temperature impedances, and piezoelectric properties was explored. It was found that the high conductivity of (Bi_0.5Na_0.5)TiO₃ (BNT) ceramics should be mainly attributed to the formation of A-site cation vacancies during sintering. Improved physical and electrical properties can be achieved in the sample with A-site cation excess. The control of the stoichiometry proves to be an effective way to improve BNT ceramics for possible application.     

Optical rib waveguide based on epitaxial Ba0.7Sr0.3TiO3 thin film grown on MgO

Barium strontium titanate (Ba_0.7Sr_0.3TiO₃, abbreviated as BST) thin films were grown on MgO (001) single crystal substrates using pulsed laser deposition. A heteroepitaxial growth relationship of <001> _BST // <001> _MgO was confirmed by X-ray diffraction. The bidimensional structure of a rib waveguide was designed using the effective index method. A BST/MgO rib waveguide was fabricated using photolithography and reactive ion etching techniques. A single-mode near-field output pattern was observed using an end-fire coupling method at a wavelength of 1550 nm, which is consistent with our numerical calculation.     

Structure and electrical properties of boron-added (Ba,Sr)TiO3 thin films fabricated by the sol-gel method

Thin films of Ba_xSr_1−xTiO₃ (BST, with x=0.5) were fabricated on a RuO₂/Ru/SiO₂/Si substrate by the spin coating of the multicomponent sol prepared using metal alkoxides. Boron alkoxide was intentionally introduced to establish a better microstructure and to reduce the leakage current. AFM indicated that a crack-free uniform microstructure having a smooth surface was gradually developed with increasing boron content. The relative dielectric permittivity of the 250-nm thick BST thin films fired at 700°C decreased with increasing content of boron, from 420 for the undoped film to 190 for the 10 mol% boron-added film at 1 MHz. This observation was interpreted in terms of a serial capacitance composed of the perovskite BST grain and the interfacial B₂O₃ glassy phase having a low dielectric permittivity. The leakage current density (J) also decreased with the amount of boron added. The leakage current for the applied voltage greater than 1 V showed a linear variation of logJ with E^1/2 at room temperature, suggesting that the interface-controlled Schottky emission was the dominant conduction process for the BST thin films fabricated on the RuO₂ electrode.