Dielectric Properties Of Er Research Articles

Crystal structures, lattice vibrational characteristics, and dielectric response of Mg3(VO4)2 microwave dielectric ceramics sintered at different temperatures

Mg3(VO4)2 (MVO) microwave dielectric ceramics were fabricated by a conventional solid-state sintering method at different sintering temperatures (Ts) between 1000 °C and 1100 °C. The effects of Ts on the phase evolution, the crystal structures, the dielectric responses, and the lattice vibrational characteristics of MVO were investigated. XRD patterns after Rietveld refinement were applied to analyze the phase evolution and the crystal structures of the samples, which shows the orthorhombic structure with the space group of Cmca for the MVO ceramics. Micrograph from scanning electron microscopy shows a uniform and dense crystal structure with the highest bulk density for the MVO sample sintered at 1050 °C. Raman scattering spectroscopy and infrared reflectance spectroscopy were used to dissect the lattice vibrational characteristics of the MVO ceramics. There are two types of vibrational modes of the MVO samples, i.e., the external modes caused by the deformation of [VO4]3- and the rotational and translational vibrations of the lattices, the internal modes attributed to the asymmetric stretching vibrations of V-O bonds. The intrinsic dielectric properties were determined by fitting the data with a four-parameter semi-quantum (FPSQ) model. Modes 1, 2, and 4, associated with the external modes, have the greatest contribution coefficient of 65.58% to the dielectric constant, and Mode 1 has the greatest contribution coefficient of 51.40% to the dielectric loss. The structure-property relationships were semi-quantitatively mathematically established according to the Raman modes. The MVO sample sintered at 1050 °C has the best dielectric properties of εr = 9.59 and Q × f = 41,193 GHz (f = 13.69 GHz).

Temperature stable dielectric properties of Mg2TiO4–MgTiO3–CaTiO3 Ceramics Over a Wide Temperature range

The zero resonant frequency temperature coefficient (τf) of microwave dielectric ceramics (MWDCs) at high and low temperature have attracted great attention in the development of microwave communication equipment. In this work, the Mg2TiO4–MgTiO3–CaTiO3 (MMC) ceramics with meeting the application requirements of 5G communication were prepared by traditional solid-phase sintering after investigating the relationship among phase compositions of xMg2TiO4-(0.931-x)MgTiO3-0.069CaTiO3 and 0.34Mg2TiO4-0.591MgTiO3-yCaTiO3, sintering process, and dielectric properties in detail. The results show that the dielectric properties of MMC ceramics are strongly affected by the phase relative contents of MgTiO3, Mg2TiO4 and CaTiO3. For instance, MMC ceramics with approximate τf = 0 is contributed by mutual compensation of Mg2TiO4 and MgTiO3, in which the Mg2TiO4 phase plays an important role in decreasing the τf value; and the increase of CaTiO3 will greatly increase the εr value for MMC ceramics, while has a negative effect in the Q × f value. After three-phase regulation, the 0.32Mg2TiO4-0.611MgTiO3-0.069CaTiO3 microwave dielectric ceramic has a better dielectric temperature stability, associated with dielectric properties of εr = 19.7, Q × f = 55,400 GHz (at 8.43 GHz), τf- = 4.5 ppm/°C (−40 °C–25 °C), and τf+ = −5.1 ppm/°C (25 °C–90 °C).

Phase composition, microstructure and dielectric properties of middle-fired LiF-doped MgTi(1− x )Zr x O3 ceramics

LiF-doped MgTi(1− x )Zr x O3 (0.05 ≤ x ≤ 0.20) ceramics were fabricated via a conventional solid-state reaction route. All samples displayed MgTiO3 phase accompanying with a little of ZrO2 and Mg2TiO4 as the second phase. The lattice constant increased with increasing x due to the substitution of Zr4+ for Ti4+. The densification temperatures were reduced to the range of 1100–1150 °C due to LiF-doping. The microwave dielectric property of MgTi(1− x )Zr x O3 ceramics depended on the substitution content of Zr4+. Typical, MgTi0.90Zr0.10O3 ceramic exhibited microwave dielectric properties of εr = 18.7, tanδ = 2.8 × 10−4, and Q × f = 34300 GHz.

Fabrication of Wideband Low‐Profile Dielectric Patch Antennas from Temperature Stable 0.65 CaTiO3–0.35 LaAlO3Microwave Dielectric Ceramic

AbstractIn this paper, the medium dielectric constant 0.65CaTiO3‐0.35LaAlO3(CTLA) composite microwave ceramic is employed to introduce in dielectric patch antennas (DPA). Typical, high‐performance microwave dielectric properties ofεr ≈ 44.8,Q × f ≈ 43 950 GHz@3.67 GHz andTCF ≈ 0 ppm °C–1can be obtained by solid‐state reaction method in CTLA composite microwave ceramics sintered at 1450 °C for 2 h. Then, the CTLA composite ceramic patch fired with silver coating is mounted on the Rogers RO4003C substrate operating as a magnetic wall boundary. A simplified cavity‐like theoretical model is used to analyze the proposed DPA structure and the accuracy of this antenna model is evaluated by the theoretical results from a commercial CST Microwave Studio 2019. Based on this, the CTLA composite ceramic physical property is modified to enhance the radiation efficiency and reduce profile of the DPA. The higher‐order TM121mode is brought close to the dominant TM101mode by taking advantage of the multimode characteristics of the dielectric patch resonator and introducing a sintered silver slot in the ceramic dielectric patch. For demonstration, the proposed DPA prototype operating in the multiprobe antenna near the field measurement system is implemented and measured.

Influence of Ca2+ substitution for Ba2+ on the crystal structure and microwave dielectric properties of Ba1−xCax(Mg1/3Ta2/3)O3 ceramics

The Ba1–xCax(Mg1/3Ta2/3)O3 (BCMT, 0 ≤ x ≤ 0.05) microwave dielectric ceramics were synthesized by the conventional solid-state ceramic route. In this paper, the effects of Ca2+ substituting for Ba2+ on the phase structure, microstructure, and microwave dielectric properties of Ba1–xCax(Mg1/3Ta2/3)O3 ceramics were investigated. X-ray diffraction (XRD) exhibited that the Ba1–xCax(Mg1/3Ta2/3)O3 ceramics possessed the main phase Ba(Mg1/3Ta2/3)O3 (BMT) when 0 ≤ x ≤ 0.05 and secondary phase Ba0.5TaO3 for x = 0.05. SEM micrographs showed that the substitution of Ca2+ for Ba2+ could increase the grain size. The apparent density was influenced by the concentration of liquid phases caused by the substitution of Ca2+ for Ba2+ ions. The microwave dielectric properties depended heavily on apparent density, B-site cation ordering degree, Ba-deficient, secondary phase and distortion of oxygen octahedral. Finally, Ba1–xCax(Mg1/3Ta2/3)O3 (x = 0.04) ceramics sintered at 1450 °C for 8 h showed superior microwave dielectric properties of er = 24.1, Q × f = 165,800 GHz and τf = 0.12 ppm/℃.

Structure instability and high microwave dielectric permittivity of nonstoichiometric (Sr0.4Ce0.4)1-xNdxTi0.8Mg0.2O3 system for wireless communication

(Sr0.4Ce0.4)1-xNdxTi0.8Mg0.2O3 [(SC)NdTMgO3, x = 0.1–0.4] non-stoichiometric system were obtained through conventional solid-state synthesis technique. All perovskite peaks were attributed to either single (x ≤ 0.3) and/or mixed (x = 0.4) like phases. A solid solution of cubic structure was obtained for x ≤ 0.2, however, for x ≥ 0.3, the (SC)NdTMgO3 compound, exhibits structure instability and (200)/(310) peaks splitting. The peaks splitting indicates cubic (C-phase) to tetrogonal (T-phase) structure phase transition. All ceramic samples appear nearly dense, presenting a non-uniform grain size distribution. The observed trend of the microwave dielectric properties (εr, τf, Q × f) is mainly related to the formation of structure phase transition, packing fraction, relative density and ionic polarizability. A key microwave (MW) dielectric properties of εr = 53, Q × f = 26,700 GHz and τf = +2.8 pmm/°C could be obtained for composition with x = 0.4.

Crystal structure, infrared spectra, and microwave dielectric properties of low-firing Nd2Zr3(MoO4)9 ceramics prepared by reaction-sintering process

Low temperature-sintered ceramics Nd2Zr3(MoO4)9 were successfully prepared via reaction-sintering method. The sintering behavior, microwave dielectric properties, crystal structure, and microstructure were analyzed systematically. XRD and Rietveld refinement results revealed that all samples formed a pure trigonal structure phase with the space group of R-3c. Density determination showed that ceramics possessed the highest relative density when sintered at 800 °C for 6 h. SEM image further confirmed that ceramics possessed dense and homogeneous microstructure at the optimum sintering temperature 800 °C. Far infrared spectra analysis showed the structural phonon oscillation at infrared region played an important role in polarization. Nd2Zr3(MoO4)9 ceramics obtained the optimum microwave dielectric properties of er= 10.01, Q × f = 55,923 GHz, τf= − 13.81 ppm/ °C when sintered at 800 °C for 6 h.

Sintering Behavior and Microwave Dielectric Properties of LiF-Doped Li2Mg3Ti0.95(Mg1/3Ta2/3)0.05O6 Ceramics for LTCC Applications

Low-firing 1–4 wt.% LiF-doped Li2Mg3Ti0.95(Mg1/3Ta2/3)0.05O6 (LMTT) ceramics were synthesized via solid state reaction method. The effects of LiF on the phase composition, sintering behavior as well as microwave dielectric properties were systematically discussed. Adding LiF additives could lower the sintering temperature to 950°C for LMTT ceramics. X-ray powder diffraction analysis indicated that all the compounds prepared in this work have cubic symmetry with space group Fm-3m. Typically, LMTT with 2 wt.% LiF exhibited a dense uniform microstructure and optimized microwave dielectric properties of er ∼ 15.1 (± 0.2), Q·f ∼ 60,100 GHz (at 8.3 GHz), and τf ∼ − 20.45 ppm/°C at 950°C. In addition, the good chemical compatibility with Ag electrode made LMTT-2 wt.% LiF ceramic an appropriate candidate for low temperature co-fired ceramic.

Phase compositions, microstructures, and microwave dielectric properties of Li2Zn3Ti4O12-based temperature stable materials modified by CaTiO3 additions

In present work, the microwave dielectric properties of CaTiO3-added Li2Zn3Ti4O12 ceramics prepared by the conventional solid-state method have been investigated. The phase composition, microstructure and microwave dielectric properties of (1 − x) Li2Zn3Ti4O12–x CaTiO3 (x = 3, 4, 5, 6 and 7 wt%) ceramics were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), EDS and network analyzer. The XRD and EDS results indicated that the ceramics involved Li2Zn3Ti4O12 and CaTiO3 phases. The SEM micrographs shown that as the CaTiO3 contents increased, the average grain size of the composition ceramics decreased. The microwave dielectric properties of the composition ceramics can be effectively controlled by varying the CaTiO3 contents. The values of dielectric constant (er) and τf of the composition ceramics were increased, and the quality factor (Q × f) was decreased with increasing the CaTiO3 contents. Typically, a new temperature stable microwave dielectric material of 0.94 Li2Zn3Ti4O12–0.06 CaTiO3 with excellent microwave dielectric properties of er = 21.7, Q × f = 61,490 GHz, and τf = + 2.68 ppm/°C was attained when sintered at 1175 °C for 4 h.

Synthesis, microstructure and microwave dielectric properties of Li2Mg3SnO6 ceramics with excess lithium

The sintering behavior, microstructure and microwave dielectric properties of Li2(1+ x )Mg3SnO6 ceramics were investigated in order to prepare dense phase-pure ceramics samples. The phase structures, density variation and pore morphology were especially correlated with the subsequent microwave dielectric properties. The experimental results showed that single phase rock-salt structure Li2Mg3SnO6 ceramics were obtained for x = 0.08. The actual sample density and microstructure (grain and pores) strongly depended on Li content x. The increasing in εr and Q×f values may be caused by increasing bulk density, reducing porosity as well as increasing grain boundaries. Well-densified Li2.16Mg3SnO6 ceramics were obtained with excellent microwave dielectric properties of εr = 11.4, Q×f = 140660 GHz and τf = -40.5 ppm/°C at 1360 °C.

Loss evolution of hexagonal Ba0.6Sr0.4La4Ti4O15 microwave dielectric ceramics

In the present work, Ba0.6Sr0.4La4Ti4O15 (BSLT) ceramics with and without the sintering aid (1 wt% ZnO + 0.25 wt% WO3) were synthesized via the solid-state reaction method. Microwave loss evolutions of Ba0.6Sr0.4La4Ti4O15 were investigated emphatically utilizing thermally stimulated depolarization current (TSDC). The sintering behavior, crystal structure and microwave dielectric properties were contrasted mutually. X-ray diffraction confirms that single phase solid solutions are achieved with a hexagonal perovskite structure. And the addition of the sintering aid causes the movement of diffraction peaks to low angles. Due to the incorporation into lattice, the sintering characteristic has not been improved by the sintering aid. With ZnO and WO3, BSLT sintered at 1500 °C demonstrates microwave dielectric properties of er = 46, Qf = 21,100 GHz and τf = − 4.6 ppm/°C. Especially, the Qf value displays an obvious drop from 48,600 to 21,100 GHz, thus a near zero τf value may be achieved. The extrinsic loss mechanism associated with defects chemistry is explored and TSDC spectra indicate a distinct difference induced by the sintering aid. It can be manifested that the Qf variation originates in the different concentration of oxygen vacancies in host dielectrics.

The effect of sintering agents on the sinterability and dielectric properties of Li2Mg3TiO6 ceramics

ABSTRACTThe low-fired Li2Mg3TiO6 ceramics were fabricated via doping several multicomponent sintering agents. The effect of multicomponent sintering agents on the sinterability and microwave dielectric properties of Li2Mg3TiO6 ceramics were investigated. The results showed that the densification temperature of Li2Mg3TiO6 ceramics was reduced to 950°C, 975°C and 1000°C by doping LC, LV and LB as sintering agents, respectively. The optimum dielectric properties of ϵr = 15.7, Q × f = 70100 GHz and τf = −43 ppm/°C were obtained at 950°C for LC-doped Li2Mg3TiO6 ceramics. Such sample was compatible with Ag electrodes, suitable for the low-temperature co-fired ceramics (LTCC) applications.

Effect of Nd<sub>2</sub>O<sub>3</sub> on the Microwave Dielectric Properties of 0.67CaTiO<sub>3</sub>-0.33LaAlO<sub>3</sub> Ceramics

0.67CaTiO3-0.33LaAlO3 ceramics doped with Nd2O3 were prepared using a conventional two-step solid-state reaction, and the effect of Nd2O3 doping on the microwave dielectric properties were studied. A single phase of perovskite structure was confirmed with the Nd2O3 doping. The results showed that the addition of Nd2O3 obviously improved the density and Q×f values of CTLA ceramics. The dielectric constant were almost not affected and the τf values were close to zero with the increase of the doping amount. CTLA ceramics with 0.2 wt% Nd2O3 doping sintered at 1380 °C for 4 h exhibited the optimal microwave dielectric properties of εr = 45.36, Q×f = 37,890 GHz, τf = 7.80 ppm/°C.

Reaction-sintering method for microwave dielectric Li2CoTi3O8 ceramic

ABSTRACTLi2CoTi3O8 ceramic was prepared by a reaction-sintering method for the first time and its microwave dielectric properties were investigated. A single phase of the Li2CoTi3O8 ceramic was confirmed by its XRD pattern. The variation of microstructures was analyzed by SEM. The optimum sintering condition of Li2CoTi3O8 was considered to be 1050°C/5 h, for the best density and dielectric properties. Typically, Li2CoTi3O8 ceramic prepared by a reaction-sintering method sintered at 1050°C for 5 h exhibited microwave dielectric properties of ϵr = 22.3, Q × f = 28860 GHz and τf = −5.0 ppm/e°C. The correlation between dielectric properties and microstructure is also discussed.

Microwave dielectric properties and thermally stimulated relaxations of Ba0.6Sr0.4La4Ti4O15−TiO2 composite ceramics by flowing oxygen sintering

Phase structure, sintering behavior, microwave dielectric properties and thermally stimulated relaxations of the 0.93Ba0.6Sr0.4La4Ti4O15−0.07TiO2 composite ceramics were investigated through using flowing oxygen atmosphere sintering. Ba0.6Sr0.4La4Ti4O15 (BSLT) sintered at 1500 °C possesses microwave dielectric properties of er = 44, Q × f = 45,000 GHz and τ f = −7.5 ppm/°C. Rutile TiO2 with er = 105, Q × f = 46,000 GHz, τ f = +465 ppm/°C was combined with the BSLT to compensate the negative τ f value in current research. XRD reveals that the ceramic samples possess a hexagonal perovskite structure and a secondary phase of TiO2−δ. The 0.93BSLT−0.07TiO2 compounds sintered in flowing oxygen exhibit small grain sizes and some pores, which are less compactly sintered compared with the ones sintered in air. The densification, grain growth and microwave dielectric properties of 0.93BSLT−0.07TiO2 have a clear dependence on sintering temperature. The 0.93BSLT−0.07TiO2 composite ceramics sintered at 1500 °C possess good microwave dielectric properties: er = 47.2, Q × f = 32,400 GHz and τ f = −3.3 ppm/°C. The extrinsic loss mechanism associated with defects was explored by relying on thermally stimulated depolarization current (TSDC) measurement. It can be manifested that TSDC relaxations are mostly derived from oxygen vacancies and TSDC spectra are evidently affected by the sintering temperature.

Broadband and Microwave Dielectric Studies on Ba5Nb4O15 Ceramics Supplemented with Its Nanoparticles for Cryogenic Electronic Applications

Ba5Nb4O15 (BNO) nanopowders were prepared by sol–gel process. The effect of BNO nanopowders (x = 1 wt.%, 2 wt.%, and 3 wt.%) on micron-sized BNO polycrystalline powders were studied systematically. Transmission electron microscope (TEM) images of BNO nanoparticles revealed spherical and cylindrical shapes with average particle sizes of 45 nm and 60 nm, respectively. Further, the dielectric response of BNO ceramics with x wt.% of nanosized particles (x = 1–3) measured in the temperature range of 80°C to 200°C showed relaxation behaviour and is described by using Havriliak–Negami equation. The best microwave dielectric properties of er and Q × f0 values of 39.2 GHz and 59,000 GHz, at 6.52 GHz are obtained for the x = 3 wt.% sample, sintered at 1100°C, and is attributed to maximum density, large and uniform microstructure. The acquired static dielectric response of BNO ceramics with x wt.% of nanosized particles (x = 1–3) are suitable for cryogenic electronic and dielectric resonator applications.

Low temperature reaction-sintering and microwave dielectric properties of ZnO–Nb2O5–2TiO2 ceramics

Low-temperature fired ZnO–Nb2O5–2TiO2 ceramics co-doped with CuO–V2O5 were fabricated by a reaction-sintering process. CuO–V2O5 addition effectively lowered the sintering temperature of ZnO–Nb2O5–2TiO2 ceramics to 950°C due to the liquid phase sintering. The phase compositions and microwave dielectric properties of ZnO–Nb2O5–2TiO2 ceramics depended on the CuO–V2O5 content and sintering temperatures. Typically, 1.5 wt% CuO–V2O5 co-doped ceramics sintered at 950°C for 5 h exhibited optimum microwave dielectric properties of er = 45.9, Q × f = 12,200 GHz, τf = −1.8 ppm/°C. In addition, such sample was compatible with Ag electrode, suitable for the low-temperature co-fired ceramics (LTCC) applications.

Sintering behavior and microwave dielectric properties of TiO2 added Ba4(Sm0.5Nd0.5)28/3Ti18O54 ceramics with K2O–B2O3–SiO2 glass

K2O–B2O3–SiO2 (KBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for Ba6–3x(Sm1-y, Ndy)8+2xTi18O54 + 2TiO2 (x = 2/3 and y = 0.5; BSNTT) ceramics. Effects of KBS doping on sintering behavior, microstructure and microwave dielectric properties of BSNTT ceramic were investigated. The appropriate KBS addition significantly lowered the sintering temperature of BSNTT ceramic with slightly damaging its microwave dielectric properties. The X-ray diffraction results showed that all the well sintered samples exhibited the main phase Ba(Sm,Nd)2Ti4O12 and a certain amount of Ba2Ti9O20 and TiO2 secondary phases. Besides, the other secondary phase Sm2Ti2O7 formed when 9 wt% KBS added. Then the scanning electron microscopy micrographs of the optimally well-sintered (1075 °C for 3 h) ceramics showed a dense microstructure. With the increasing content of KBS addition, both the dielectric constant (er) and quality factor (Q × f) value decreased. At last, the good microwave dielectric properties of er = 68.8, Q × f = 6766 GHz, τf = 28.76 ppm/°C were obtained for BSNTT + 5 wt% KBS ceramic sintered in air at 1075 °C for 3 h.

A new microwave dielectric material ZnZr0.8Sn0.2Nb2O8

A novel low-loss microwave dielectric material ZnZr0.8Sn0.2Nb2O8 was reported for the first time. The samples were prepared by the conventional solid-state reaction route and sintered in the temperature range of 1225–1325 °C for 6 h. Single phase ZnZr0.8Sn0.2Nb2O8 was obtained and it showed monoclinic structure. The microstructure and microwave dielectric properties were investigated systematically. The variation trend of dielectric constant (e r ) was in accordance with variation trend of relative density. The Qf value mainly depended on the crystal structure and it increased with the increasing packing fraction. The temperature coefficient of resonant frequency (τ f ) correlated with the variation of bond valence of B-site. The excellent microwave dielectric properties of e r = 27.37, Q × f = 76,814 GHz (where f = 7 GHz), and τ f = −55.09 × 10−6/ °C were obtained for ZnZr0.8Sn0.2Nb2O8 ceramics sintered at 1275 °C for 6 h.

Influence of soaking time on microstructures and dielectric properties of ZnO–MgO–TiO2–CaO ceramics

ZnO–MgO–TiO2–CaO (ZMTC) ceramics were prepared by a conventional solid-state method and sintered at 1150 °C for various soaking times. The density, particle sizes and dielectric constant simultaneously increase with the soaking time. On the contrary, the dielectric loss of ZMTC ceramics declines with the soaking time. The XRD analysis revealed that CaTiO3 phase nearly appears with prolonging the sintering time. With increasing soaking time, the density and er values increased, saturating at 1150 °C for 7 h with excellent dielectric properties of er = 22.4, tanδ = 0.6 × 10−4, and TCF = 24.8 ppm/°C.