Effect of TiO2 Ratio on the Phase and Microwave Dielectric Properties of Li2ZnTi3+x O8+2x Ceramics

Low-loss materials Li₂ZnTi_3+x O_8+2x (LZT) (x = 0, 0.10, 0.17, 0.25, 1.00) were prepared by the conventional solid-state route. The effect of TiO₂ ratio on phase composition, microstructure, and the microwave dielectric properties of Li₂ZnTi_3+x O_8+2x ceramics were investigated using x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Vector Network Analyzer. The results revealed that a two-phase system Li₂ZnTi₃O₈-TiO₂ was formed. The appropriate content of TiO₂ ratio can effectively adjust the temperature coefficient of the resonant frequency (τ _f) value from ?14.5 to 0 ppm/ °C without obvious degradation of the microwave dielectric properties. The microwave dielectric properties of the Li₂ZnTi_3+x O_8+2x materials were characterized at microwave frequencies. Typically, the Li₂ZnTi_3+x O_8+2x (x = 0.17) ceramic sintered at 1,160 °C for 5 h showed excellent microwave dielectric properties with ε _r = 28.51, Q × f = 58,511 GHz, and τ _f = + 2.3 ppm/ °C.     

Investigation of Structural and Electrical Properties of B-Site Complex Ion (Mg1/3Nb2/3)4+-Modified High-Curie-Temperature BiFeO3-BaTiO3 Ceramics

B-site complex ion (Mg_1/3Nb_2/3)-modified high-temperature ceramics 0.71BiFeO₃-0.29BaTi_1?x (Mg_1/3Nb_2/3) _x O₃ (BF-BTMNx) have been fabricated by the conventional solid-state reaction method. The compositional dependence of the?phase structure, electrical properties, and depolarization temperature of the ceramics was studied. The main phase structure of BF-BTMNx ceramics is perovskite phase with pseudocubic symmetry. The experimental results show that the dielectric and piezoelectric properties, and temperature stability strongly depend on the (Mg_1/3Nb_2/3)⁴⁺ content. The optimum (Mg_1/3Nb_2/3) content enhances the piezoelectric properties, Curie temperature, and depolarization temperature. The ceramic with x = 1% exhibited enhanced electrical properties of d ₃₃ = 158 pC/N and k _p = 0.322, combined with high-temperature stability with Curie temperature of T _c = 453°C and depolarization temperature of T _d = 400°C. These results show that the ceramic with x = 1% is a promising lead-free high-temperature piezoelectric material.     

Preparation, Characterization, and Microwave Dielectric Properties of Sr2La3Nb1−x Ta x Ti4O17 (0 ≤ x ≤ 1) Ceramics

Sr₂La₃Nb_1?x Ta _x Ti₄O₁₇ (0 ≤ x ≤ 1) ceramics were processed via a solid-state mixed oxide route. Sr₂La₃Nb_1?x Ta _x Ti₄O₁₇ (0 ≤ x ≤ 1) solid solutions were single phase in the whole range of x values within the x-ray diffraction (XRD) detection limit. The microstructure comprised elongated and needle-shaped grains. The ceramics exhibit relative permittivity (ε _r) of 73 to 68.6, product of unloaded quality factor and resonant frequency (Q _u f ₀) of 7100 GHz to 9500 GHz, and temperature coefficient of resonant frequency (τ _f) of 78.6 ppm/°C to 56.6 ppm/°C.     

Phase, Microstructure, and Microwave Dielectric Properties of NaCa4−x Sr x Nb5O17 (x = 0 to 4) Ceramics

A series of A₅B₅O₁₇-type NaCa_4?x Sr _x Nb₅O₁₇ (x = 0 to 4) compounds were processed through a solid-state mixed-oxide route. All the compositions formed dense single-phase ceramics within the detection limit of an in-house x-ray diffraction facility when sintered at 1300°C. The substitution of Sr for Ca changed the crystal symmetry from monoclinic (x = 0) to orthorhombic (x = 1 to 4) along with a slight increase in molar cell volume due to the relatively larger ionic radius of Sr. The relative permittivity (ε _r) and temperature coefficient of resonance frequency (TCF) increased from 46 to 84 and from ?117 ppm/°C to +377 ppm/°C, respectively, while the quality factor (Q × f) decreased from 11,063 GHz to 559 GHz with an increase in x from 0 to 4. Optimum properties were achieved for NaCa₃SrNb₅O₁₇, which exhibited ε _r = 57, Q × f = 4628 GHz, and TCF = ?41 ppm/°C. Compounds in the NaCa_4?x Sr _x Nb₅O₁₇ series exhibited high ε _r and Q × f with adjustable TCF; however, further work is required for simultaneous optimization of all three properties.     

Effect of CuO Addition on Microwave Dielectric Properties of 0.80Sm(Mg0.5Ti0.5)O3-0.20Ca0.8Sr0.2TiO3 Ceramics

The effects of CuO addition on phase composition, microstructure, sintering behavior, and microwave dielectric properties of 0.80Sm(Mg_0.5Ti_0.5)O₃-0.20 Ca_0.8Sr_0.2TiO₃(8SMT-2CST) ceramics prepared by a conventional solid-state ceramic route have been studied. CuO addition shows no obvious influence on the phase of the 8SMT-2CST ceramics and all the samples exhibit pure perovskite structure. Appropriate CuO addition can effectively promote sintering and grain growth, and consequently improve the dielectric properties of the ceramics. The sintering temperature of the ceramics decreases by 50°C by adding 1.00 wt.%CuO. Superior microwave dielectric properties with a ε _r of 29.8, Q × f of 85,500 GHz, and τ _f of 2.4 ppm/°C are obtained for 1.00 wt.%CuO doped 8SMT-2CST ceramics sintered at 1500°C, which shows dense and uniform microstructure as well as well-developed grain growth.     

Effect of the Addition of B2O3 on the Density, Microstructure, Dielectric, Piezoelectric and Ferroelectric Properties of K0.5Na0.5NbO3 Ceramics

Boron oxide (B₂O₃) addition to pre-reacted K_0.5Na_0.5NbO₃ (KNN) powders facilitated swift densification at relatively low sintering temperatures which was believed to be a key to minimize potassium and sodium loss. The base KNN powder was synthesized via solid-state reaction route. The different amounts (0.1–1 wt%) of B₂O₃ were-added, and ceramics were sintered at different temperatures and durations to optimize the amount of B₂O₃ needed to obtain KNN pellets with highest possible density and grain size. The 0.1 wt% B₂O₃-added KNN ceramics sintered at 1,100 °C for 1 h exhibited higher density (97 %). Scanning electron microscopy studies confirmed an increase in average grain size with increasing B₂O₃ content at appropriate temperature of sintering and duration. The B₂O₃-added KNN ceramics exhibited improved dielectric and piezoelectric properties at room temperature. For instance, 0.1 wt% B₂O₃-added KNN ceramic exhibited d ₃₃ value of 116 pC/N which is much higher than that of pure KNN ceramics. Interestingly, all the B₂O₃-added (0.1–1 wt%) KNN ceramics exhibited polarization–electric field (P vs. E) hysteresis loops at room temperature. The remnant polarization (P _r) and coercive field (E _c) values are dependent on the B₂O₃ content and crystallite size.     

Synthesis and Characterization of Li-Modified AgTaO3

(Li _x Ag_1?x )TaO₃ (0 ≤ x ≤ 0.15) ceramics were fabricated by a mixed-oxide solid-state sintering route. Compositions with x ≤ 0.1 sintered into single-phase compounds and could be indexed according to the rhombohedral, \( R{\bar{3}}c \) or R3c structure. For x > 0.1, x-ray diffraction revealed second-phase formation, probably LiTaO₃ and Ag₂Ta₈O₂₁. It was noticed that the metastable and stable phase solubility limits for Li in AgTaO₃ were x < 0.05 and 0.10 < x < 0.15, respectively. Raman and dielectric measurements confirmed the existence of a ferroelectric state in the compositions with x ≥ 0.05. This triggering of ferroelectricity supports the premise that substitution of relatively smaller ions increases the displacement of the A-site cation. The transition temperature was found to increase as a function of increasing Li concentration. Low-temperature (<100 K) Raman spectra and electron diffraction indicated that Li-doped AgTaO₃ ceramics seem to adopt new tilt systems.     

Cu<Subscript>3</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript>: An Ultralow-Firing Microwave Dielectric Ceramic with Good Temperature Stability and Chemical Compatibility with Aluminum

An ultralow-firing microwave dielectric ceramic Cu₃Mo₂O₉ with orthorhombic structure has been fabricated via a solid-state reaction method. X-ray diffraction analysis, Rietveld refinement, Raman spectroscopy, energy-dispersive spectrometry, and scanning electron microscopy were employed to explore the phase purity, crystal structure, and microstructure. Pure and dense Cu₃Mo₂O₉ ceramics could be obtained in the sintering temperature range from 580°C to 680°C. The sample sintered at 660°C for 4 h exhibited the highest relative density (～ 97.2%) and best microwave dielectric properties with ε _r = 7.2, Q × f = 19,300 GHz, and τ _f = ? 7.8 ppm/°C. Chemical compatibility with aluminum electrodes was also confirmed. All the results suggest that Cu₃Mo₂O₉ ceramic is a promising candidate for use in ultralow-temperature cofired ceramic applications.     

Thermally Stable BaTiO3-Bi(Mg0.75W0.25)O3 Solid Solutions: Sintering Characteristics,Phase Evolution,Raman Spectra,and Dielectric Properties

(1 ? x)BaTiO₃-xBi(Mg_0.75W_0.25)O₃ [(1 ? x)BT-xBMW, 0.02 ≤ x ≤ 0.24] ceramics were synthesized by a two-step solid-state reaction technique. X-ray diffraction (XRD) patterns show that a systematic structure evolution from tetragonal to pseudocubic phase was observed at x = 0.07. Raman spectra analysis illustrates that a change in average structure was observed with increasing x, and the local crystal symmetry which deviated from the idealized cubic perovskite structure appeared as x ≥ 0.07. Temperature dependence of dielectric properties indicates that the phase transition temperature (T _c) decreased with increasing x. Moreover, (1 ? x)BT-xBMW (0.07 ≤ x ≤ 0.24) ceramics show good dielectric thermal stability over a wide temperature range, which indicates that these ceramics are candidates for thermal stability devices.     

Effect of MnO2 Addition on the Electrical Properties of PNZST Ceramics

(Pb_0.99Nb_0.02)[(Zr_0.70Sn_0.30) _x Ti_1?x ]_0.98O₃ (PNZST) piezoelectric ceramics of pure perovskite structure were prepared by a conventional ceramic fabrication method, where x = 0.48–0.56. When x = 0.52, the ceramics exhibit a high piezoelectric coefficient (d ₃₃ ～ 490), but the mechanical quality factor (Q _m) is only 72. To increase the Q _m and not dramatically lower the d ₃₃, MnO₂ was chosen as the additive. The effects of adding MnO₂ on the sinterability, structure, and electrical properties of PNZST ceramics were investigated in detail. With a small addition of MnO₂ (≤0.6 wt.%), the Mn ions are homogeneously dissolved in the PNZST ceramic, leading to full densification when sintered at 1,300 °C. However, further addition of MnO₂ prevents densification, causing a high porosity and small grain size. The doping of MnO₂ transforms the phase structure from tetragonal to rhombohedral. The addition of MnO₂ up to a maximum of 0.6 wt.% remarkably improves the mechanical quality factor (Q _m) of PNZST ceramics, simultaneously as well as maintaining a high d ₃₃ and k _p. PNZST with 0.6 wt.% MnO₂ exhibits excellent electrical properties with piezoelectric coefficient d ₃₃ = 392 pC/N, electromechanical coupling factor k _p = 0.60, mechanical quality factor Q _m = 1,050, dielectric constant ε _r = 1,232, dielectric dissipation tanδ = 0.0058, and Curie temperature T _C = 300 °C.     

MnO2-Modified Ba(Ti,Zr)O3 Ceramics with High Q m and Good Thermal Stability

MnO₂-modified Ba(Ti_0.9625Zr_0.0375)O₃ ceramics have been prepared by the conventional solid-state reaction technique at different sintering temperatures. Room-temperature piezoelectric properties, thermal stability, and crystalline structures were investigated. It was found that both the MnO₂ additive and sintering temperature significantly influence the piezoelectric properties of the MnO₂-modified Ba(Ti_0.9625Zr_0.0375)O₃ ceramics. The sample sintered at 1400°C exhibited the best room-temperature piezoelectric properties of Q _m = 1907, d ₃₃ = 205 pC/N, and k _p = 40.5% with tan δ = 0.46%, and its k _p remains larger than 35% in the broad temperature range from ?38°C to 65°C. The results indicate that MnO₂-modified Ba(Ti_0.9625Zr_0.0375)O₃ ceramics are promising lead-free materials for frequency device and power device applications.     

Structural and magnetic properties of Dy3+ doped Y3Fe5O12 for microwave devices

The Dy³⁺ doped Y_3−xDy_xFe₅O₁₂ (x=0–3) nanopowders were prepared using microwave hydrothermal route. The structural and morphological studies were analyzed using transmission electron microscope, X-ray diffractometer and field emission scanning electron microscope. The nanopowders were sintered at 900 °C/90 min using microwave furnace. Dense ceramics with theoretical density of around 95% was obtained. Ferro magnetic resonance (FMR) spectrum and microwave absorption spectrum of Dy³⁺ doped YIG were studied, the signal exhibits a resonance character for all Dy³⁺ variations. It was observed that the location of the FMR signal peak at the field axes monotonically shifts to higher field with increasing Dy³⁺ content. The dielectric and magnetic properties (ε′, ε′′, µ′ and µ′′) of Dy³⁺ doped YIG were studied over a wide range of frequency (1–50 GHz). With increase of Dy³⁺ both ε′ and µ′ decreased. The low values of dielectric, magnetic properties and broad distribution of FMR line width of these ceramics are opening the real opportunity to use them for microwave devices above K- band frequency.     

Diffuse Phase Transition and Electrical Conductivity of Pb(Ca1/3Nb2/3)O3

The lead-based relaxor ceramic Pb(Ca_1/3Nb_2/3)O₃ was prepared by two-step solid-state reaction. The material stabilizes in the orthorhombic phase with refined lattice parameters a = 3.4814 Å, b = 12.9480 Å, and c = 14.2483 Å. The scanning electron micrograph is indicative of heterogeneous grain distribution with average grain size ~0.8–2.0 μm. The temperature-dependent dielectric response has a broad peak at 233.5°C (at 1 kHz, ε′ = 14523). A frequency-dependent shift toward higher temperature with increasing frequency is attributed to relaxor behaviour. Deviation from the Curie–Weiss law is observed at temperatures higher than the temperature, T _m, at which the dielectric constant is maximum. The modified Curie–Weiss law was used to fit the dielectric data; the results were indicative of almost complete diffuse phase transition characteristics. The dielectric relaxation obeys the Vogel–Fulcher relationship with freezing temperature T _f = 214.1°C, activation energy E _a = 0.16 eV, and relaxation frequency ν ₀ = 3.4 × 10⁷ Hz. Electrical conduction is mainly attributed to the hopping mechanism.     

Microstructure and Electrical Properties of K0.5Na0.5NbO3-LiSbO3-BiFeO3-x %molZnO Lead-Free Piezoelectric Ceramics

Lead-free piezoelectric ceramics {0.996[(0.95(K_0.5Na_0.5)NbO₃-0.05LiSbO₃]-0.004BiFeO₃}-xmol%ZnO were prepared through a conventional ceramics sintering technique. The effect of ZnO content on structure, microstructure, and piezoelectric properties of KNN-LS-BF ceramics was investigated. The results reveal that ZnO as a sintering aid is very effective in promoting sinterability and electrical properties of the ceramics sintered at a low temperature of 1,020 °C. The ceramics show a single-perovskite structure with predominant tetragonal phase, and coexistence of orthorhombic and tetragonal phases is observed for x = 2.5–3.0. The addition of ZnO causes abnormal grain growth. A dense microstructure is also obtained at x = 2.0 because the relative density reaches up to 94.6 %. The morphotropic phase boundary and dense microstructure lead to significant enhancement of the piezoelectric properties. The ceramic with x = 1.5 exhibits optimum electrical properties as follows: d ₃₃ = 280 pC/N, k _p = 46 %, Q _m = 40.8, P _r = 25 μC/cm², E _c = 1.2 kV/mm, and T _c = 340 °C.     

Influence of Li-B-Si Additions on the Sintering and Microwave Dielectric Properties of Ba-Nd-Ti Ceramics

Li₂O-B₂O₃-SiO₂ (LBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for tungsten-bronze-type Ba₄Nd_9.3Ti₁₈O₅₄ (BNT) ceramic. The effects of LBS additions on the sintering behaviors, microstructures, and microwave dielectric properties of the BNT ceramic have been investigated, indicating that LBS addition obviously lowered the sintering temperature of the BNT ceramic without damaging its microwave dielectric properties. BNT ceramic doped with 3 wt.% and 4 wt.% LBS addition could be well sintered at 975°C and 950°C for 3 h and had excellent properties: ε _r = 65.99, Q × f = 4943 GHz (f = 4.4 GHz), τ _f = 19 ppm/°C, and ε _r = 64.56, Q × f = 4929 GHz (f = 4.3 GHz), τ _f = 11 ppm/°C, respectively.     

Enhancing Piezoelectric Performance of CaBi2Nb2O9 Ceramics Through Microstructure Control

Calcium bismuth niobate (CaBi₂Nb₂O₉, CBN) is a high-Curie-temperature (T _C) piezoelectric material with relatively poor piezoelectric performance. Attempts were made to enhance the piezoelectric and direct-current (DC) resistive properties of CBN ceramics by increasing their density and controlling their microstructural texture, which were achieved by combining the templated grain growth and hot pressing methods. The modified CBN ceramics with 97.5% relative density and 90.5% Lotgering factor had much higher piezoelectric constant (d ₃₃ = 20 pC/N) than those prepared by the normal sintering process (d ₃₃ = 6 pC/N). High-temperature alternating-current (AC) impedance spectroscopy of the CBN ceramics was measured by using an impedance/gain-phase analyzer. Their electrical resistivity was approximately 6.5 × 10⁴ Ω cm at 600°C. Therefore, CBN ceramics can be used for high-temperature piezoelectric applications.     

Density,Electrical and Optical Properties of Yttrium-Containing Tellurium Bismuth Borate Glasses

60B₂O₃-30Bi₂O₃-(10 ? x) TeO₂-xY₂O₃ mol.% (x = 0, 0.1, 1, 2 and 5) glasses have been prepared by the conventional glass-melting technique. The influence of Y₂O₃ on the density, optical and electrical properties of the glass was investigated. The density decreased whereas the molar volume increased with increasing Y₂O₃. Optical transmission in the ultraviolet (UV) spectral region indicated that the values of direct and indirect optical band gap energies increased, which was attributed to structural changes induced by the addition of Y₂O₃. Urbach energy values decreased with increasing the Y₂O₃, which was attributed to a decrease in the broadening due to static disorder-related parts. Fourier transform infrared (FTIR) spectra revealed that the addition of Y₂O₃ transforms BO₄ to BO₃ and BiO₃ to BiO₆ groups. The decrease in the dc and ac electrical conductivities was attributed to the formation of [BiO₆] units which leads to a decrease in acceptor levels of Bi⁵⁺ sites. The electric modulus formalism indicated that the conductivity relaxation at different frequencies was a temperature-independent dynamic process. The full width at half-maximum (FWHM) of the normalized modulus decreases with increasing Y₂O₃ content, suggesting that the decrease of the Y ion–ion distance increases the interaction between the Y ions.     

Electrical characteristics of MOSFETs with La2O3/Y2O3 gate stack

A metal oxide semiconductor field effect transistor (MOSFET) with ultra-thin La₂O₃/Y₂O₃ high-k gate dielectric was fabricated. The effects of thermal treatment process on both physical and electrical characteristics of the La₂O₃/Y₂O₃ stack were studied using XPS and electrical measurements. It was observed that the effective mobility of the fabricated MOSFETs with La₂O₃/Y₂O₃ gate stack was not degraded with increasing the annealing temperatures up to 600 °C. X-ray photoelectron spectroscopy (XPS) analysis also revealed that the formation of SiO₂ and silicate layer at the interface was suppressed in La₂O₃/Y₂O₃ stack compare to that of in La₂O₃ single layer. Obtained results suggesting that La₂O₃/Y₂O₃ gate stack is one of the promising candidates for high-k gate insulator to be used in the future metal oxide field effect transistors.     

Atomic layer deposition of high capacitance density Ta2O5-ZrO2 based dielectrics for metal-insulator-metal structures

We have investigated electrical properties of laminated atomic layer deposited films: ZrO₂-Ta₂O₅, ZrO₂-Nb₂O₅-Ta₂O₅, ZrO₂-Ta_xNb_1−xO₅ and Ta₂O₅-Zr_xNb_yO_z. Even though the capacitances of laminates were often higher compared to films of constituent materials with similar thickness, considerably higher charge storage factors, Q, were achieved only when tetragonal ZrO₂ was stabilized in ZrO₂-Ta₂O₅ laminate and when the laminate thickness exceeded 50 nm. The decreased Q values in the case of most laminates were the result of increased leakage currents. In the case of thinner films only Ta₂O₅-Zr_xNb_yO_z stack possessed capacitance density and Q value higher than reference HfO₂. Concerning the conduction mechanisms, in the case of thinner films, the Ta₂O₅ or Ta_xNb_1−xO₅ apparently controlled the leakage either by Richardson-Schottky emission or Poole-Frenkel effect.     

Study on BMT Millimeter Wave Dielectric Resonators

The microwave dielectric properties and microstructures of Ba(Mg_1/3Ta_2/3)O₃ (BMT) ceramics were investigated. In order to reduce the evaporation of MgO at high temperature, burying in MgO powders sintered BMT ceramics. The relationship between the composition and Q value of BMT ceramics was discussed. Dielectric resonators using in millimeter wave band have been designed and fabricated. Their attenuations at central resonation frequency (τ_f) are less than 35dB. Temperature coefficients of resonant frequency are adjustable and less than 2 ppm/°C.