Low Temperature Dielectric Properties Research Articles

Low-temperature sintering and microwave dielectric properties of LiF-doped Zn1.8SiO3.8 ceramics

Low-temperature sintering and microwave dielectric properties of LiF-doped Zn1.8SiO3.8 ceramics

Investigation low-temperature densification and dielectric properties of glass/Al2O3/nano-TiO2 ceramics for microwave applications

Investigation low-temperature densification and dielectric properties of glass/Al2O3/nano-TiO2 ceramics for microwave applications

Low-Temperature Sintering and Microwave Dielectric Properties of CuxZn1-xTi0.2Zr0.8Nb2O8 Ceramics with the Aid of LiF.

M2+N4+Nb2O8-type ceramics (where M = Mg, Ca, Mn, Co, Ni, Zn and N = Ti, Zr) are essential for satellite communication and mobile base stations due to their medium relative permittivity (εr) and high quality factor (Q × f). Although ZnTi0.2Zr0.8Nb2O8 ceramic exhibits impressive microwave dielectric properties, including an εr of 29.75, a Q × f of 107,303 GHz, and a τf of -24.41 ppm/°C, its sintering temperature of 1150 °C remains a significant barrier for integration into low-temperature co-fired ceramic (LTCC) technologies. To overcome this limitation, a strategy involving the partial substitution of Zn2+ with Cu2+ and the addition of LiF as a sintering aid was devised for ZnTi0.2Zr0.8Nb2O8. The dual impact of Cu2+ partial substitution and LiF as a sintering enhancer facilitated the successful sintering of Cu0.3Zn0.7Ti0.2Zr0.8Nb2O8 ceramics at a reduced temperature of 950 °C using the conventional solid-state reaction method. These ceramics exhibited excellent microwave dielectric properties. Notably, Cu0.3Zn0.7Ti0.2Zr0.8Nb2O8 ceramic with 40 mol% LiF addition demonstrated optimal microwave dielectric properties without any reaction with a silver electrode at a sintering temperature of 950 °C, yielding εr = 32, Q × f = 45,543 GHz, and τf = -43.5 ppm/°C.

Unveiling the effect of phase separation on crystallization of calcium borosilicate glass-ceramics

The CaO–B2O3–SiO2(CBS) glass-ceramics with low sintering temperature and good microwave dielectric properties have been applied on the famous commercial low temperature co-fired ceramics (LTCC) Tape for passivation substrate materials for 5G/6G technology. However, the phase separation and its relationship with the crystallization is rarely studied but extremely important for understanding and designing the high-performance CBS glass-ceramics. Herein, we find that the phase separation type of CBS glass-ceramics changes from metastable immiscibility to stable immiscibility with the increase of B2O3 content. In the metastable immiscible glass-ceramics, three phases are observed, including continuous borate-rich and silicate-rich phases as well as spherical silicate-rich phases. In the stable immiscible glass-ceramics, the silicate-rich phases transform into petal-liked shapes. β-CaSiO3 nuclei are formed in fractions with BO3/SiO4 equaling to 0.56. Notably the β-CaSiO3 nucleus do not grow after heat treatment at 850 °C, but grow at higher temperatures. Phase separation hinders the precipitation of β-CaSiO3 and promoted the formation of CaB2O4 and SiO2. In addition, interfacial defects caused by phase separation alter the crystal barrier and promote the formation of α-CaSiO3. However, α-CaSiO3 dissolves at 1000 °C and may provide Ca2+ cations together with the borate-rich phase for the regrowth of β-CaSiO3. Our work provides another perspective for understanding the effects of phase separation on crystallization in CBS glass-ceramics, contributing to improving the microwave dielectric performance by structural design.

Low-temperature sintering and microwave dielectric properties of ZnGa2–xO4–1.5x ceramics with added B2O3

Low-temperature sintering and microwave dielectric properties of ZnGa2–xO4–1.5x ceramics with added B2O3

Low sintering temperature and microwave dielectric properties of H3BO3-added Li2Ti0.85(A1/3Ta2/3)0.15O3 (A = Zn, Mg) ceramics for patch antenna application

Li2Ti0.85(A1/3Ta2/3)0.15O3 + xwt.% H3BO3 (A = Zn, Mg; 1.0 ≤ x ≤ 5.0) (LTATBx) ceramics were fabricated by the traditional solid phase synthesis method. The LTATBx ceramics belong to monoclinic structure which was checked by the X-ray diffraction (XRD). The microstructure of Li2Ti0.85(A1/3Ta2/3)0.15O3 ceramics could be improved by the addition of H3BO3, which was directly observed by the scanning electron microscope (SEM). The optimum dielectric properties (107,490 GHz and 57,543 GHz) of Li2Ti0.85(A1/3Ta2/3)0.15O3 ceramics were obtained when the x values are equal to 1.0 and 3.0, respectively. Since the addition amount reached 5.0, the sintering temperature declined to 900 °C and 950 °C, respectively. The patch antennas prepared with LTZTB1.0 and LTMTB3.0 ceramics were simulated and measured. The results from measured indicated that the S11 parameters in LTZTB1.0 and LTMTB3.0 based patch antenna are less than −15.0 dB, and the VSWR is close to 1.0, which basically meets the application requirements of external antenna.

Low-temperature sintering and microwave dielectric properties of CaMoO4 ceramics for LTCC and ULTCC applications

Low-temperature co-fired ceramic (LTCC) technology can meet the requirements of device miniaturization and integration. In this work, a novel series of CaMoO4 + x wt.% Li2MoO4 (CMO+ xLMO, x = 0.0–2.5) microwave dielectric ceramics were prepared. The sintering temperature of CMO ceramic significantly declines from 1050 °C to 600 °C by adding a small amount of LMO. A dissolution-precipitation process at the grain boundary has been demonstrated to be the mechanism for low-temperature sintering through transmission electron microscopy analysis. The low-temperature sintered CMO ceramics present excellent microwave dielectric properties, e.g. CMO+ 1.0 wt.% LMO ceramics sintered at 600 °C, εr ∼ 14.4, Q×f ∼ 13,060 GHz, τƒ ∼ − 41.0 ppm/°C; CMO+ 2.5 wt.% LMO ceramics sintered at 700 °C, εr ∼ 15.1, Q×f ∼ 16,122 GHz, τƒ ∼ − 43.8 ppm/°C, which show great potentials in both LTCC and ULTCC applications.

Effect of A- and B-site doping on the low-temperature dielectric and impedance properties of BaTiO3-based ceramics

Effect of A- and B-site doping on the low-temperature dielectric and impedance properties of BaTiO3-based ceramics

Effect of Li2CO3–Bi2O3 doping on the low-temperature sintering, structure, and dielectric and mechanical properties of MgO–TiO2(w) ceramics

Dense MgO–12% TiO2(w) ceramics containing 12 wt% TiO2, which were doped with Li2CO3–Bi2O3 composite sintering aids, were prepared at a low sintering temperature of 950 °C in this study. The effects of sintering additives on the sintering characteristics, phase composition, microstructure, and dielectric and mechanical properties of the ceramic samples were systematically investigated, and the influences of their phase composition and microstructure on the dielectric and mechanical properties were examined. The introduction of sintering aids produced a new Bi4Ti3O12 phase in the sample structure, while the residual Bi2O3 mixed with the newly formed Mg2TiO4 and Bi4Ti3O12 phases distributed at MgO grain boundaries formed a structure surrounding MgO grains. This structure filled the pores in the ceramic sample, which increased its density and enhanced the mechanical properties. At a Li2CO3–Bi2O3 content of 15 wt%, the density, flexural strength, and Vickers hardness of the ceramic samples reached their maximum values of 3.4 g/cm3, 218.9 MPa, and 778.7 HV, respectively. However, the further increase in the Li2CO3–Bi2O3 content deteriorated their dielectric properties although the dielectric constant and dielectric loss remained below 13.4 and 2.1 × 10−3, respectively. The findings of this work indicate that Li2CO3–Bi2O3 sintering aids can significantly lower the sintering temperature of MgO–12% TiO2(w) ceramics and control their dielectric and mechanical properties through microstructural changes.

Structural, optical and dielectric investigations on RECr0.85Mn0.15O3 (RE = Ho, Gd and Pr) nanoparticles

We hereby report the room-temperature structural and optical characterization of RECr0.85Mn0.15O3 (RECMO, RE = Ho, Gd and Pr) compounds synthesized by the auto-combustion sol–gel route. Their low temperature dielectric properties are also presented. The RECMO compounds crystallize in an orthorhombic Pbnm symmetry with an average grain size range of 51–80 nm. Structural analysis reveals an increase in the structural distortion compared to that of the undoped bulk compounds. Optical measurements exhibit a significant reduction in bandgap values for RECMO nanoparticles when compared with their undoped bulk compounds. Further, from the absorbance measurements various optical parameters such as skin depth, extinction coefficient, refractive index and optical conductivity were also calculated. The dielectric analysis confirms the lower values of the dielectric permittivity and dielectric loss than those of their corresponding bulk compounds. AC conductivity versus frequency and temperature data are fitted according to the Jonscher’s power law and Arrhenius law, respectively. The small polaron hopping is responsible for the electric conduction in these compounds. The tunability of the optical and dielectric properties as a result of substitution and particle size reduction makes these materials useful for various potential applications in photocatalysis, optoelectronics and low permittivity dielectrics.

Low-temperature crystallization and microwave dielectric properties of forsterite generated in MgO–SiO2 system following LiF addition

The crystallization and microwave dielectric properties of forsterite (Mg2SiO4) produced in (1-x)2MgO–SiO2(MS)-xLiF mixtures were characterized. High-temperature XRPD for a 0.91MS-0.09LiF specimen indicated the crystallization of forsterite above 800 °C, although MgSiO3, MgO and SiO2 were also detected due to the short heating duration. The XRPD patterns for (1-x)MS-xLiF ceramics sintered at 900 °C for 4 h in a covered crucible demonstrated the formation of forsterite as a single phase in compositions having x values less than 0.08. The activation energy for the crystallization fraction of forsterite was estimated from the DTA curves by using Kissinger-Akahira-Sunose method and decreased from 1382.4 to 474.0 kJ/mol, suggesting that the LiF addition enhances the nucleation and crystallization of forsterite. Refinement of the crystal structures of the (1-x)MS-xLiF ceramics by Rietveld analysis showed that the patterns acquired from samples having x values of 0.03–0.08 corresponded to a forsterite single phase with a decrease in the lattice parameters, confirming the substitution of Li and F for Mg and O in the forsterite. 7Li and 19F solid-state NMR spectroscopy analyses also confirmed the presence of 7Li and 19F signals for the sintered ceramics. The Q・f values for the ceramics increased from 22,800 to 104,800 GHz as x was increased to 0.08, due to the improvement in the crystallinity of forsterite. Although a near zero TCf value was achieved by CaTiO3 addition for (1-y)(0.92MS-0.08LiF)-yCaTiO3 ceramics at y = 0.10 (εr = 8.2, Q・f = 25,050 GHz, TCf = −5 ppm/°C), the Q・f values were drastically decreased due to the lower crystallinity of the forsterite and the presence of SiO2 and Li2MgSiO4 as secondary phases.

Anomalous Ca Content Dependence of Dielectric Properties of Charge-Ordered Pr1−xCaxMnO3 as a Signature of Charge-Ordered Phase Modulation

Low-temperature dielectric properties of charge/orbital-ordered manganite, Pr1−xCaxMnO3 for 0.40 ≤ x ≤ 0.50, was investigated systematically as a function of Ca content, x. The Ca content dependence of dielectric permittivity and dissipation factor exhibited distinct maxima near x~0.45. The overall dielectric response of charge-ordered Pr1−xCaxMnO3 was dominated by dielectric polarization induced by polaron hopping and exhibited thermally activated relaxation behaviour. The thermally activated dielectric relaxation behaviour over the investigated temperature range was further analysed with the help of two models: the small polaron hopping model and the Mott three-dimensional variable range hopping model. The estimated polaron transport parameters also displayed non-monotonic variation with x and exhibited a broad minima between x = 0.425 and 0.45. Considering the previous work reported so far, the charge order pattern of Pr1−xCaxMnO3 below x = 0.425 was most likely to be of Zener-polaron type, while near x = 0.50 was checker-board type and for in-between compositions; neither pure checker-board type nor pure Zener-polaron type can be considered a ground state. The observed results suggest that a modulation of the checkerboard-type charge/orbital ordering pattern in Pr1−xCaxMnO3 possibly takes place in the Ca content range of investigation, 0.40 ≤ x ≤ 0.50.

Effect of modification of zinc oxide nanostructures on contact angle

The hydrophobic coatings are one of the most used processes to prevent the deterioration of materials and increase its lifetime, since they have non-stick, low friction, anti-wetting, high and low temperature resistance, chemical and dielectric properties, etc. This work presents the chemical production of zinc oxide (ZnO) nanostructures that were deposited on glass substrates by two methods: spin-coating and dip-coating. The doped substrates were modified by temperature and exposure to ultraviolet light (UV). The contact angle of the surface was measured after making some modification, revealing an initial change compared to the uncoated substrate. Later, the angles were varied, comparing between the two deposition methods. The higher contact angle was presented by spin-coating sample, after rising its temperature and a first exposure to UV light; an increase of 30% was observed in comparison to the uncoated substrate; In contrast, the smallest angle was obtained in dip-coating sample after raising its temperature, reducing around 55% of its size compared to the uncoated substrate.

Low-temperature sintering and microwave dielectric properties of a new Ba/Ti-based diphase composite ceramic

Low-temperature sintering and microwave dielectric properties of a new Ba/Ti-based diphase composite ceramic

Colossal dielectric permittivity in CuCrO2 ceramics

CuCrO2 ceramics were prepared by solid-state reaction method. Low-temperature (10–320 K) dielectric properties were investigated in the frequency range of 102–106 Hz. Colossal dielectric constant behavior composed of two thermally activated relaxations was observed. The low-temperature relaxation (R1) occurring around 125 K with an activation energy of 0.21 eV was ascribed to be a dipolar relaxation caused by defect dipoles of OHO•−Cr3+. The high-temperature relaxation (R2) appearing around 200 K with an activation energy of 0.26 eV was argued to be a Maxwell-Wagner relaxation originating from humidity sensitivity.

Low temperature sintering and dielectric properties of LaAlO3–BaSnO3-based microwave dielectrics

ABSTRACT LaAlO3–BaSnO3 ceramics as a new microwave dielectric material were investigated in terms of optimum synthesis conditions and thereby the relative density, microstructure, solid-solution state, and dielectric properties with the addition of various sintering aids at different sintering temperatures. The dielectric properties of 0.9LaAlO3–0.1BaSnO3 (LA-0.1BS) were strongly influenced by relative density, microstructure, chemical ordering, and mixing rule of the dielectric constant. Densification of the LA-0.1BS ceramics was improved from 82.3 to 96.13% with an average grain size of around 1.9 µm at reduced sintering temperature by 250°C. The LA-0.1BS ceramics sintered with 3 mol% of Bi2O3–SiO2 (BS) showed dielectric constant (ϵr) ∼21.18 with associated dielectric loss (tan δ) ∼0.00824 and Q × f ∼1213.59 (10 GHz) which could be achieved at low sintering temperature of 1400–1450°C.

Low-Temperature Sintering and Microwave Dielectric Properties of a New Ba/Ti-Based Diphase Composite Ceramic

Low-Temperature Sintering and Microwave Dielectric Properties of a New Ba/Ti-Based Diphase Composite Ceramic

A low-sintering temperature microwave dielectric ceramic for 5G LTCC applications with ultralow loss

In next-generation mobile and wireless communication systems, low sintering temperature and excellent dielectric properties are synergistic objectives in the application of dielectric resonators/filters. In this work, Li2Ti0·98Mg0·02O2·96F0.04–1 wt% Nb2O5 (LTMN) ceramics were fabricated, and their sintering temperature was successfully lowered from 1120 °C to 750 °C by adjusting the mass ratio of B2O3–CuO (BC) additive. The optimum dielectric properties (ԑr ~ 24.44, Q × f ~ 60,574 GHz and τf ~ 22.8 ppm/°C) were obtained in BC-modified LTMN ceramics sintered at 790 °C. Even if their sintering temperature was lowered to 750 °C, the lowest temperature among the Li2TiO3-based dielectric ceramics currently used for LTCC technology, excellent dielectric properties (ԑr ~ 23.77, Q × f ~ 51,636 GHz) were still maintained. Additionally, no extra impurity phase was detected in BC-modified LTMN ceramics co-fired with Ag at 790 °C, indicating that BC-modified LTMN ceramics have a bright prospect in high-performance LTCC devices for 5G applications.

Investigation of low temperature dielectric properties of manganese doped-copper oxide nanoparticles by coprecipitation method

Mn-doped CuO nanoparticles were prepared by the co-precipitation method. X-ray diffraction patterns of pristine and Mn-doped CuO (5, 10 and 15%) nanoparticles confirm the formation of monoclinic structure. Scanning electron microscopy revealed that, the change in morphology with increasing Mn content. Dielectric permittivity value increases with increase in Mn concentration. AC conductivity curves depict improvement in conductivity with a low concentration of Mn content. DC conductivity and AC conductivity values are in accordance with Jonscher’s universal power law

Three‐phase borate solid solution with low sintering temperature, high‐quality factor, and low dielectric constant

AbstractThe sintering and microwave dielectric properties of a ceramic material based on the mixing of Mg3B2O6 and Zn3B2O6 have been widely studied using first‐principles calculations and experimental solid‐state reactions. Characterization methods include the Network Analyzer, X‐ray, Raman diffraction, scanning electron microscopy, energy‐dispersive spectroscopy, and differential‐thermal and thermo‐mechanical analyzer. The increasing amount of Mg2+ results in the appearance of Mg2B2O5 and ZnO, and the mutual substitution (Mg2+ and Zn2+) phenomenon has emerged in Zn3B2O6 and Mg2B2O5. The mechanisms have been explained with the help of DFT calculations. The bond parameters and electron distributions of the ZnO4 tetrahedron and MgO6 octahedron have been modified due to substitution. The sintering, substitution, and phase formation properties have been analyzed quantitatively through the energy parameters. The best dielectric properties were obtained for x = 0.20 sintered at 950°C, εr = 6.47, Q × f = 89 600 GHz (15.2 GHz), τf = −48.6 ppm/°C, relative density = 96.7%. The mixing of Zn3B2O6 and Mg3B2O6 ceramics is a feasible method to obtain a ceramic with low sintering temperature and excellent dielectric properties.