Tunable and microwave dielectric properties of Ba0.5Sr0.5TiO3-BaWO4 composite ceramics doped with Co2O3

Co₂O₃ doped BaWO₄-Ba_0.5Sr_0.5TiO₃ composite ceramics, prepared by solid-state route, were characterized systematically, in terms of their phase compositions, microstructure and microwave dielectric properties. Doping of Co₂O₃ promoted grain growth, reduced Curie temperature and broadened phase-transition temperature range of BaWO₄-Ba_0.5Sr_0.5TiO₃, which were attributed mainly to the substitution of Co³⁺ for Ti⁴⁺ at B site in the perovskite lattice. Dielectric diffusion behaviors of the composite ceramics were discussed. The composite ceramics all had dielectric tunability of higher than 10% at 30 kV/cm and 10 kHz, with promising microwave dielectric properties. Specifically, the sample doped with 0.2 wt.% Co₂O₃ exhibited a tunability of 20%, permittivity of 225 and Q of 292 (at 1.986 GHz), making it a suitable candidate for applications in electrically tunable microwave devices.     

Sintering characteristic,crystal structure and microwave dielectric properties of a novel thermally stable ultra-low-firing Na2BiMg2V3O12 ceramic

A novel ultra low-firing microwave dielectric ceramic with the composition of Na₂BiMg₂V₃O₁₂ was fabricated by a solid state reaction method. The phase structure, sintering behavior and microwave dielectric properties of ceramics were investigated. The ceramic can be well densified at 660 °C for 4 h. X-ray diffraction data show that Na₂BiMg₂V₃O₁₂ has a cubic garnet structure with lattice parameters of a = 12.4929 Å, V = 1,949.80 Å³, Z = 8 and ρ = 4.42 g/cm³. The microwave dielectric properties are strongly related to the density and morphology of the samples. The ceramic sintered 660 °C exhibits good microwave dielectric properties with ε_r = 23.2, Q × f = 3,700 GHz and τ _f  = 8.2 ppm/°C. These results indicate that Na₂BiMg₂V₃O₁₂ ceramic is a candidate for low temperature co-fired ceramics devices, such as chip multi-layer LC filter, microstrip bandpass filter, multilayer antenna.     

Structure and microwave dielectric properties of ZnTa<Subscript>2</Subscript>O<Subscript>6</Subscript> ceramics with TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript> additions

Ceramic samples based on ZnTa2O₆ and ZnTa₂O₆–MO₂ (M = Ti, Zr) systems have been obtained by the solid state ceramic route. The phase composition and microstructure of samples were investigated. The effect of the aliovalent substitution of ions Zn²⁺ and Ta⁵⁺ by M⁴⁺ (M = Ti, Zr) in the structure of ZnTa₂O₆ on microwave dielectric properties of ceramics was studied. The way of the compensation of the positive temperature coefficient of resonant frequency of dielectric resonators based on ZnTa₂O₆ ceramics with using the aliovalent substitution of cations was proposed. Dielectric resonators with the high temperature stability of the resonant frequency and high dielectric properties in the microwave range based on the ZnTa₂O₆–ZrO₂ system were obtained for application in electronics.     

Effect of heavy mixing lithium with doping of manganese on structural, EPR and dielectric spectroscopic properties of Layered Na2Ti3O7

Sintered ceramic samples of Na₂Ti₃O₇ with 50 % (1.0 Molar Percentage of Li₂CO₃ i. e. 50 % Lithium) with different doping molar percentages MnO₂ (0.0 < X<0.1) have been prepared through solid state reaction route. The microstructure, EPR, dielectric properties and ac conductivity of (NaLi)Ti₃O₇ with Mn [0.0 ≤ X≤0.1] have been investigated. The X-ray diffraction patterns of pure and doped layered ceramics suggest the crystals are orthorhombic in phase. The room temperature electron paramagnetic resonance spectra reveal that that for lower percentage of doping manganese ions occupies Ti ⁴⁺ site with oxidation state Mn³⁺, while higher percentage of manganese ions doping leads to oxidation state Mn²⁺ in interlayer mixed (Na Li) site. In both cases the charge compensation mechanism should operate to maintain the overall charge neutrality of the lattice. For all pure and doped layered ceramics, ferroelectric transition having high transition temperature has been identifying at 648 K. Manganese ion doping decreases dielectric loss and increases dielectric constant due to inhibition of domain wall motion. It is apparent that ionic conduction becomes difficult due to presence of more lithium ions with sodium ions in interlayer space which shrinking the wide space of interlayer channels.     

Intrinsic polarization and resistive leakage analyses in high performance piezo-/pyroelectric Ho-doped 0.64PMN-0.36PT binary ceramic

This paper presents in detail the ferroelectric properties of Ho-doped 0.64Pb(Mg_1/3Nb_2/3)O₃-0.36PbTiO₃ ceramic including determination of intrinsic polarization and investigation of resistive leakage. The effect of Ho³⁺ doping on the structure, dielectric, piezoelectric and ferroelectric properties of PMN-PT ceramics was studied. Perovskite phase of pure and Ho-doped 0.64Pb(Mg_1/3Nb_2/3)O₃-0.36PbTiO₃ ceramics were synthesized using solid state reaction method. Powder XRD confirmed the incorporation of Ho³⁺ ions in PMN-PT lattice. EDX spectra confirmed the existence of Ho and its homogeneity in doped-sample. The average grain size, transition temperature and dielectric loss factor (tan δ) decreased while the density and the dielectric constant of the PMN-PT ceramic increased by Ho doping. Furthermore, an increase in the ferroelectric properties and the piezoelectric coefficient (d₃₃¹, from 547 to 610?pm/V) were observed for doped sample. The ‘Remanent Hysteresis Task’ revealed that a major portion (80.42%) of the remanent polarization (P_r) is switchable in the sample which makes Ho-doped PMN-PT a potential material for memory switching devices. Time-dependent compensated (TDC) hysteresis task and fatigue test were carried out which revealed resistive leakage and fatigue free nature of Ho-doped PMN-PT ceramic. These results demonstrate that Ho-doped PMN-PT ceramic possesses excellent properties to achieve a variety of applications.     

Doping effects of Mn<Superscript>2+</Superscript> on the dielectric properties of glass-doped BaTiO<Subscript>3</Subscript>-based X8R materials

In this paper, Mn²⁺ and calcium borosilicate glass (CBS) were used as effective dopants to prepare environmentally friendly dielectric materials satisfying EIA X8R specification. The effects of various Mn²⁺ concentrations on the dielectric properties of BaTiO₃ (BT) ceramics were investigated when CBS amount was fixed. The dielectric measurements showed that the permittivity was decreased continuously with increasing Mn²⁺ concentrations, resulted from the existence of paraelectric regions caused by Mn²⁺ doping. The dielectric loss was decreased at the beginning and then increased with increasing Mn²⁺ concentrations, whereas the resistivity showed an opposite movement. The SEM images and X-ray diffraction curves corresponding to BT ceramics doped with different Mn²⁺ amounts proved that Mn²⁺ can promote the crystallization of CBS glass to form the secondary phase Ca₄Mn₄Si₈O₂₄, which determines the intensity of the high temperature peak (at about 125 °C) of the variation rate curve of capacitance. Moreover, the modification effects of Mn²⁺ on the dielectric properties of BT have been investigated. It is revealed that a proper usage of Mn²⁺ can improve the dielectric properties significantly, and Mn²⁺ and CBS co-doped BT ceramics are promising to develop X8R MLCs.     

Enhanced dielectric and electrical properties in CaZrO3-doped X8R BaTiO3-based ceramics sintered at medium temperature

Lead-free X8R BaTiO₃-based ceramics were prepared by conventional solid-state method. The influence of the composition and procedures on the microstructures, lattice parameters and dielectric properties of ceramics materials were systemically studied. XRD results indicate that no secondary phase is formed in the CaZrO₃-doped samples after sintering. The content of Ca²⁺ ions and Zr⁴⁺ ions decrease from grain boundaries to grain interiors referring to EDS results, which indicate that the ions mainly locate in the grain boundaries. The Curie temperatures of all CaZrO₃ doped samples increase due to the increasing tetragonality caused by the addition of CaZrO₃. SEM micrographs reveal that the grain size of CaZrO₃-doped BaTiO₃-based samples are not uniform, ranging from 0.2 to 0.8 µm. Furthermore, samples doped with 1.0 wt % CaZrO₃ exhibit optimal dielectric properties with high temperature stability of capacitance, due to the fine-grain microstructures. Moreover, we obtained a lead-free high performance X8R dielectric ceramic composition sintered at medium temperature (1,135 °C).     

Phase formation and microwave dielectric properties of Pb2+ and Sr2+ doped La4Ti9O24 ceramics

Phase formation and microwave dielectric properties of the Pb²⁺ and Sr²⁺ doped La₄Ti₉O₂₄ ceramics were investigated. Using electron diffraction and Rietveld analysis of the X-ray powder diffraction patterns, we show that the increase in the concentration of Pb²⁺ and Sr²⁺ doping results in the structural transition from La₄Ti₉O₂₄ to a La_2/3TiO₃-type phase (Ibmm, No. 74). A change in the crystalline phase considerably affects the microwave dielectric properties, increasing the ɛ_r from 37 to 130, reducing Q × f from 25,000 to 5500, and increasing temperature coefficient of the resonant frequency (TCF) from 15 to 300 ppm/°C.     

A new group of microwave dielectric ceramics in the RE(Ti0.5W0.5)O4 [RE=Pr, Nd, Sm, Gd, Tb, Dy, and Y] system

RE(Ti_0.5W_0.5)O₄ [RE=Pr, Nd, Sm, Gd, Tb, Dy, and Y] ceramics have been prepared as single-phase materials by a conventional solid-state ceramic route. The ceramics have been characterized by X-ray diffraction and microwave methods. The RE(Ti_0.5W_0.5)O₄ ceramics showed an increase in cell volume and a corresponding decrease in density with ionic radius of RE³⁺ ions. The dielectric constant varies from 21 to 25, Q_u×f from 6000 to 11 000 GHz and _f from –5 to –22 ppm °C^–1. The microwave dielectric properties indicate that these materials are possible candidates for dielectric resonator as well as substrate applications in microwave integrated circuits.     

Improvement in quality factor of (Zr0.8Sn0.2)TiO4 microwave ceramics by Mn doping

Highly dense, good quality microwave dielectrics based on Mn⁴⁺ doped ZST have been prepared with ZST nanopowder without using any sintering aid. Single phase orthorhombic crystalline structure has been confirmed by XRD pattern. The room temperature dielectric constant remains almost unchanged in the low and microwave frequency regions (1 MHz to 9.3 GHz). A significant change in the microwave dielectric properties of ZST ceramics was observed with increasing Mn⁴⁺. There was almost four times increase in quality factor with Mn⁴⁺ doping in ZST ceramics.     

Preparation and dielectric properties of BaCu(B2O5)-doped SrTiO3-based ceramics for energy storage

BaCu(B₂O₅) (BCB) was used as sintering aids to lower the sintering temperature of multi-ions doped SrTiO₃ ceramics effectively from 1300 °C to 1075 °C by conventional solid state method. The effect of BCB content on crystalline structures, microstructures and properties of the ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements, respectively. The addition of BCB enhanced the breakdown strength (BDS) while did not sacrifice the dielectric constant. The enhancement of BDS should be due to the modification of microstructures, i.e., smaller and more homogeneous grain sizes after BCB addition. The dielectric constant of BCB-doped ceramics maintained a stable value with 1.0 mol% BCB, which was dominated by the combination of two opposite effects caused by the presence of second phases and the incorporation of Cu²⁺ and Ba²⁺, while further increase was owing to the increase of dissolved Ba²⁺ ions when the content of BCB is more than 2.0 mol%. The multi-ions doped SrTiO₃ ceramics with 1.0 mol% BCB addition showed optimal dielectric properties as follows: dielectric constant of 311.37, average breakdown strength of 28.78 kV/mm, discharged energy density of 1.05 J/cm³ and energy efficiency of 98.83%.     

Influence of different dopant sites by lanthanum on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

The effects of La³⁺ doped in calcium copper titanate (CCTO) at Ca²⁺ site and Cu²⁺ site were examined. The doped compositions, La_0.1Ca_0.85Cu₃Ti₄O₁₂ (LCCTO) ceramics and CaLa_0.1Cu_2.85Ti₄O₁₂ (CLCTO) ceramics were prepared by the solid-state method. The microstructure, dielectric properties, complex impedance and nonlinear I–V characteristics were studied. And it was found that La³⁺ doped at Ca²⁺ site achieved lower sintering temperatures than that doped at Cu²⁺ site in CCTO ceramics. The dielectric loss (tan δ) of LCCTO ceramics was about 0.05 at 40 kHz when the sample was sintered at 1080 °C. Dielectric constant (ε′) of LCCTO ceramics was about 3.2 × 10⁴ when the sample was sintered at 1100 °C, which was larger than CLCTO ceramics examined under the same process condition with sintering temperatures vary. The impedance analysis revealed that LCCTO ceramics had an influence of resistance of grain boundaries, which was stronger than that of CLCTO ceramics. Meanwhile, both LCCTO ceramics and CLCTO ceramics had a nonlinear-Ohmic property.     

Effect of Bi2O3 doping on the dielectric properties of medium-temperature sintering BaTiO3-based X8R ceramics

Medium-temperature sintering X8R ceramics were fabricated based on BaTiO₃-based ceramics with Bi₂O₃ additives. The effects of sintering aids Bi₂O₃ on crystalline structure and electrical properties of BaTiO₃-based ceramics were investigated. The sinterability of BaTiO₃ ceramics was significantly improved by adding Bi₂O₃, whose densification sintering temperature reduced from 1,260 to 1,130 °C. However, the dielectric constant (ε) of BaTiO₃-based ceramics doped with Bi₂O₃ was decreased dramatically. Both low ε phase Bi₄Ti₃O₁₂ and the decrease of the tetragonality (c/a ratio), which are demonstrated by XRD pattern, are resulted in the decrease of ε. The ε of samples doped with 5.5 wt% Bi₂O₃ was higher than the other doped samples. The substitution of Bi³⁺ for the Ba²⁺ in BaTiO₃ resulted in the increase of electrovalence (from +2 to +3) of A-site ion, so the attractive force between A and B (Ti⁴⁺) sites becomes stronger. Thus Ti⁴⁺’s polarization enhances, then ε was increased to some extent. The X8R BaTiO₃-based ceramics could be sintered at as low as 1,130 °C by doping 5.5 wt% Bi₂O₃ additives into the BaTiO₃-based ceramics, with a ε greater than 2,430 at 25 °C, dielectric loss lower than 1.3 % and temperature coefficient of capacitance <±15 % (?55–150 °C).     

Microstructure and dielectric properties of BST/MZO ceramic composites for tunable microwave applications

Ba_0.6Sr_0.4TiO₃/Mg_0.9Zn_0.1O (BST/MZO) ceramic composites with different MZO contents were prepared by traditional ceramic process. The crystal structure, fracture surface morphology, and dielectric properties were systematically investigated. The results show that the BST/MZO ceramic composites possess diphase structure, dense, and uniform morphology. The composites have relatively low dielectric loss (in the order of 10⁻³) at microwave frequency. The ceramics all retain substantial tunability (more than 20% at 8 kV/mm DC field) and excellent dielectric strength (more than 19.5 kV/mm). The BST-50 wt% MZO sample has the optimal FOM value (about 256) and should be a better candidate for tunable microwave applications.     

Sintering characteristic and microwave dielectric properties of ultra-low loss Li<Subscript>2</Subscript>Mg<Subscript>3</Subscript>TiO<Subscript>6</Subscript> ceramic prepared by reaction-sintering process

Microwave dielectric properties and microstructures of ultra-low loss Li₂Mg₃TiO₆ ceramic prepared by reaction-sintering method (RS) and conventional solid-state reaction method (CS) have been investigated. The XRD patterns and SEM images revealed that the single phase of Li₂Mg₃TiO₆ and uniform morphology are obtained by both RS and CS methods at the optimal sintering temperatures. In order to further investigate the effects of different sintering methods on the microwave dielectric properties of Li₂Mg₃TiO₆ ceramics, the oxide polarizabilities and packing fraction were calculated based on the Rietveld refinement. The calculation results revealed that the RS method was more beneficial to the microwave dielectric properties of Li₂Mg₃TiO₆ ceramics in comparison with CS method. Excellent microwave dielectric properties for Li₂Mg₃TiO₆ ceramics with enhanced Q?×?f value of 157,036 GHz could be obtained using RS method sintered at 1250 °C for 6 h.     

Microwave dielectric properties of Bi(Sc<Subscript>1/3</Subscript>Mo<Subscript>2/3</Subscript>)O<Subscript>4</Subscript> ceramics for LTCC applications

A novel microwave dielectric ceramics Bi(Sc_1/3Mo_2/3)O₄ with low firing temperature were prepared via the solid reaction method. The specimens have been characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and DC conductivity. The Bi(Sc_1/3Mo_2/3)O₄ ceramics showed B-site ordered Scheelite-type structure with space group C2/c. Raman analysis indicated that prominent bands were attributed to the normal modes of vibration of MoO₄ ^2? tetrahedra. The dielectric loss of Bi(Sc_1/3Mo_2/3)O₄ ceramics can be depended strongly the bulk conductivity by DC measurement. The superior microwave dielectric properties are achieved in the Bi(Sc_1/3Mo_2/3)O₄ ceramic sintered at 875 °C/4 h, with dielectric constant?~?25, Q?×?f ~?51,716 GHz at 6.4522 GHz and temperature coefficient of resonance frequency ~???70.4 ppm/°C. It is a promising microwave dielectric material for low-temperature co-fired ceramics technology.     

Effect of starting raw materials on the dielectric, ferroelectric and electro-shape-memory properties of Mn3+ doped (Pb40Sr60)TiO3 ceramics

The effect of starting raw materials on the dielectric, ferroelectric and electro-shape-memory properties of 0.5 mol% Mn³⁺ doped (Pb₄₀Sr₆₀)TiO₃ ceramics was systematically studied. SEM observation showed that the ceramics fabricated from Pb₃O₄, SrCO₃, TiO₂ and MnCO₃ possessed the most homogeneous microstructure and the largest grain size. As the macroscopic consequence, such ceramics exhibited large dielectric property and well-developed double hysteresis loop. More interestingly, it showed large digital-like recoverable electrostrain of 0.11 % under the electric field of 3 kV/mm, which can rival the widely used linear piezoelectricity of the hard PZT ceramics. Defect distribution within the large and homogenous grains was analyzed to explore the microscopic origin of the simultaneous domain switching behavior and the digital-like strain properties. Such feature indicated the importance of material processing on the on/off-characterized electromechanical applications.     

Studies on the structure and properties of semiconductor ceramic cooling materials

Thermoelectric polycrystalline ceramic materials were prepared by a new ceramic technology. Samples of p-type 72% Sb₂Te₃ + 25% Bi₂Te₃ + 3% Sb₂Se₃ doped with tellurium and 90% Bi₂Te₃ + 5% Sb₂Te₃ + 5% Sb₂Se₃ doped with Sbl₃ or Agl were studied. The new ceramic cooling materials have an inhomogeneous structure, but higher mechanical strength and thermoelectric properties. The method is simpler than the Bridgman and powder metallurgy processes. Measurements of properties show that sintering temperature and time effect the thermoelectric properties of the samples. Scanning electron microscopy shows that the polycrystalline ceramic materials have an obvious layered structure. The doping of the materials was studied, including doping variety and doping concentration. The figure of merit for n-type doped with Sbl₃ is 2.9 × 10^–3 K^–1, while that for p-type doped with tellurium is 3.1 × 10^–1 K^–1.     

Microstructures and Dielectric Properties of Ba1-xSrxTiO3 Ceramics Doped with B2O3-Li2O Glasses for LTCC Technology Applications

Ba1-xSrxTiO3 ceramics, doped with B2O3-Li2O glasses have been fabricated via a traditional ceramic process at a low sintering temperature of 900 ℃ using liquid-phase sintering aids. The microstructures and di- electric properties of B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have been investigated systemat- ically. The temperature dependence dielectric constant and loss reveals that B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have di?usion phase transformation characteristics. For 5 wt% B2O3-Li2O glasses doped Ba0.55Sr0.45TiO3 composites, the tunability is 15.4% under a dc-applied electric field of 30 kV/cm at 10 kHz; the dielectric loss can be controlled about 0.0025; and the Q value is 286. These composite ceramics sintered at low temperature with suitable dielectric constant, low dielectric loss, relatively high tunability and high Q value are promising candidates for multilayer low-temperature co-fired ceramics (LTCC) and potential microwave tunable devices applications.     

Effects of a site substitution of bivalent ions on Ag(Nb0.8Ta0.2)O3 ceramics

Bivalent ions equivalent substitution and equimolar substitution for Ag⁺ in silver niobate tantalate ceramic were studied, which will result in Ag_0.98A_0.01(Nb_0.8Ta_0.2)O₃ and Ag_0.98A_0.02 (Nb_0.8Ta_0.2)O₃ respectively, where A²⁺ = Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺, Pb²⁺. The samples were synthesized by traditional solid method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of a little Ag⁺ (in mol ratio 2 %) on the dielectric properties in Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺, Pb²⁺ substituted samples, and the influences of radius and ionic electronegativity on the dielectric properties were discussed. The results showed that the substitution of most bivalent ions except large Ba²⁺ ions for a little Ag⁺ (in mol ratio 2 %) showed no obvious change on the perovskite structure and microstructure of Ag(Nb_0.8Ta_0.2)O₃ ceramics. Basically, the dielectric properties of equivalent substituted samples were better than that of equimolar equimolar substituted samples, Ca²⁺ equivalent substituted samples showed lower dielectric loss, and Cu²⁺ equivalent substituted samples showed higher dielectric constant.