MgO–TiO2–ZnO–CaO ceramics: effect of milling process on dielectric properties

The effect of grain size on the dielectric properties of MgO–TiO₂–ZnO–CaO ceramics is investigated. Attrition milling is chosen to obtain nanometre particle size from micrometre particle size powders. Additionally, the present study is focused on the effect of the nature of milling balls on ε_r, tanδ, and the temperature coefficient of capacitance (abbreviated as TCC). For that, three kinds of balls are tested: Ф1, Ф2 or Ф5 mm stabilised zirconia balls. For the samples milled by Ф2 mm balls for 10 h, the ceramics sintered at 1,270 °C showed favorable dielectric properties with ε_r = 22.6, tanδ = 1.3 × 10^?5, and TCC = 19.1 ppm/°C.     

Effect of TiO2 on the sintering temperature and dielectric properties of Li2O–MgO–ZnO–B2O3–SiO2 ceramic composites for LTCC applications

Journal of Materials Science: Materials in Electronics - The effects of injecting TiO2 to a Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS) microwave dielectric composite on sinterability,...     

Effects of MgO on properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC applications

Li₂O–Al₂O₃–SiO₂ (LAS) glass–ceramics for low temperature co-fired ceramics (LTCC) application were prepared by melting method, and the effects of MgO on the sinterability, microstructure, dielectric property, thermal expansion coefficient (CTE) and mechanical character of this glass–ceramics have been studied. The X-ray diffraction images represent that the main phase is β-spodumene solid solutions. And some ZrO₂ and CaMgSi₂O₆ phases in LAS glass–ceramics are detected. The LAS glass–ceramics without additive (MgO) sintered at 800° had the dielectric properties: dielectric constant (ε_r) of 5.3, dielectric loss (tanδ) of 2.97 × 10^?3 at 1 MHz, CTE value of 1.06 × 10^?6 K^?1, bulk density of 2.17 g/cm³, and flexural strength of 73 MPa. 5.5 wt% MgO-added LAS glass–ceramic achieves densification at 800° exhibited excellent properties: low dielectric constant and loss (ε_r = 7.1, tanδ = 2.02 × 10^?3 at 1 MHz), low CTE (2.89 × 10^?6 K^?1), bulk density = 2.65 g/cm³ as well as high flexural strength (145 MPa). The results indicate that the addition of MgO is helpful to improve the dielectric and mechanical properties. The formation of CaMgSi₂O₆ crystal phase with higher CTE leads to the increase of CTE value of LAS glass–ceramics due to the increasing MgO content, and the increase of CTE is favourable for matching with silicon (3.1 × 10^?6 K^?1). The prepared LAS glass–ceramics have the potential for LTCC application.     

Low temperature sintering and dielectric properties of Li2ZnTi3O8–TiO2 composite ceramics doped with CaO–B2O3–SiO2 glass

The effects of CaO–B₂O₃–SiO₂ (CBS) glass addition on the sintering temperature and dielectric properties of Li₂ZnTi₃O₈–TiO₂ (LZT) composite ceramics have been investigated. Due to the compensating effect of rutile TiO₂ (τ_f ≈ +450 ppm/ °C), the temperature coefficient of resonant frequency (τ_f) for Li₂ZnTi₃O₈ + 4 wt% TiO₂ with biphasic structure was adjusted to a value near zero. The pure LZT ceramics were usually sintered at high temperature of about 1,160 °C. It was found in our experiment that a small amount of CBS glass additives could effectively lower the sintering temperature of LZT ceramics to 900 °C. With increasing the content of CBS glass, both of dielectric constant (ε_r) and quality factor (Q × f) value decreased. Typically, the 1 wt% CBS glass added Li₂ZnTi₃O₈ + 4 wt% TiO₂ ceramic sintered at 900 °C for 4 h exhibited good microwave dielectric properties of ε_r = 26.9, Q × f = 23,563 GHz and τ_f = ?1.5 ppm/ °C, which made it promising for low temperature co-fired ceramics technology application.     

Microstructure and microwave dielectric characteristics of CaO–B2O3–SiO2 glass ceramics

CaO–B₂O₃–SiO₂ (CBS) glass powders are prepared by traditional glass melting method, whose properties and microstructures are characterized by Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the pure CBS glass ceramics possess excellent dielectric properties (ε _r = 6.5, tan δ = 5 × 10⁻³ at 10 GHz), but a higher sintering temperature (>900 °C) and a narrow sintering temperature range (about 10 °C). The addition of a low-melting-point CaO–B₂O₃–SiO₂ glass (LG) could greatly decrease the sintering temperature of CBS glass to 820 °C and significantly enlarge the sintering temperature range to 40 °C. The CBS glass ceramic with 30 wt% LG glass addition sintered at 840 °C exhibits better dielectric properties: ε _r ≈ 6, tan δ < 2 × 10⁻³ at 10 GHz, and the major phases of the sample are CaSiO₃, CaB₂O₄ and SiO₂.     

Effects of SrO–B2O3–SiO2 glass additive on the microstructure and dielectric properties of CaCu3Ti4O12

The effect of SrO–B₂O₃–SiO₂ glass additive (SBS) on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics was investigated. This SBS–added CCTO ceramics were prepared by the solid state reaction. The undesirable impurity phases Ca₃SiO₅ started appearing in the XRD patterns, suggesting a possible chemical reaction between CaTiO₃ and SiO₂ (the devitrification production of SBS glass). The SBS glass additive promoted the grain growth and densification of CCTO ceramics. Cole–Cole plots of conductance suggested that the resistivity grain boundary decreased with increasing amount of SBS glass (when x = 0–2 wt%), then increased (when x = 2–3 wt%). The addition of SBS glass was desirable to increase the dielectric constants (up to 10⁴) and lowered the dielectric losses of CCTO over the frequency range of 450–40 kHz at the relatively lower sintering temperature for relatively shorter sintering time (1,050 °C, 12 h).     

Microwave dielectric properties of CaO–La2O3–Nb2O5–TiO2 ceramics

A series of ceramics with a general formula Ca_1+xLa_4?xNb_xTi_5?xO₁₇ (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇ coexisted and a trace amount of second phase was detected. The ceramics showed high ε _r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ _f value in the range between ?38 and ?126.4 ppm/°C. τ _f of CaLa₄Ti₅O₁₇ can be tuned to a near-zero value by addition of suitable amount of TiO₂.     

Influence of Al2O3/SiO2 ratio on the microstructure and properties of low temperature co-fired CaO–Al2O3–SiO2 based ceramics

In this work, in order to obtain the materials for low temperature co-fired ceramics applications, CaO–Al₂O₃–SiO₂ (CAS) based ceramics were synthesized at a low sintering temperature of 900 °C. The influences of Al₂O₃/SiO₂ ratio on the microstructure, mechanical, electrical and thermal properties were studied. According to the X-ray diffractomer and scanning electron microscopy results, the addition of the Al₂O₃ is advantageous for the formation of the desired materials. Anorthite(CaAl₂Si₂O₈) is the major crystal phase of the ceramics, and the SiO₂ phase is identified as the secondary crystal phase. No new crystal phase appears in the ceramics with the increasing Al₂O₃ content. More or less Al₂O₃ addition would all worsen the sintering, mechanical and dielectric properties of CAS based ceramics. The ceramic specimen (Al₂O₃/SiO₂ = 20/18.5) sintered at 900 °C shows good properties: high bending strength = 145 MPa, low dielectric constant = 5.8, low dielectric loss = 1.3 × 10^?3 and low coefficient of thermal expansion value = 5.3 × 10^?6 K^?1. The results indicate that the prepared CAS based ceramic is one of the candidates for low temperature co-fired ceramic applications.     

Effect of Bi4B2O9 addition on the sintering temperature and microwave dielectric properties of BaO–Nd2O3–4TiO2 ceramics

The effects of Bi₄B₂O₉ addition on the sintering temperature, phase transition and microwave dielectric properties of BaO–Nd₂O₃–4TiO₂ (BNT) ceramics have been investigated. With 10 wt% Bi₄B₂O₉ addition, the sintering temperature of the BNT ceramics can be lowered down to about 1,150 °C. The secondary phase was observed at the level of 15 wt% Bi₄B₂O₉ addition. The Bi₄B₂O₉ addition can significantly affects the microwave dielectric properties. The Q × f ₀ value is a function of the sintering temperature and the Bi₄B₂O₉ content. For the samples sintered at 1,150 °C, Q × f ₀ value varies from 6,300 to 3,300 GHz as the Bi₄B₂O₉ addition increases from 5 to 20 wt%. The addition of Bi₄B₂O₉ does not induce much degradation in ε_r but modified the τ_f value to near zero. Typically, When 10 wt% Bi₄B₂O₉ is added, the τ_f of the ceramics could be tuned to a near-zero value (~1.2 ppm/°C), a substantial ε_r (~86) and Q × f ₀ (~4,670 GHz) could also be achieved simultaneously. The Bi₄B₂O₉ is an efficient sintering additive to decrease the sintering temperature and tune the τ_f value of the microwave dielectric materials for the practical microwave applications.     

Microwave dielectric properties and low-temperature sintering of (Zn0.8Mg0.2)2SiO4–TiO2 ceramics with Li2O–B2O3

Effects of Li₂O–B₂O₃ on the sintering behavior and the microwave dielectric properties of (Zn_0.8Mg_0.2)₂SiO₄–TiO₂ ceramics were investigated as a function of Li₂O–B₂O₃ content and sintering temperature. The Li₂O–B₂O₃ combined additives successfully reduced the sintering temperature of (Zn_0.8Mg_0.2)₂SiO₄–TiO₂ ceramics from 1,250 °C to 900 °C. With the increase of Li₂O–B₂O₃ content, the TiO₂ phase decreased and the unknown second phase increased, which led to the dielectric constant (ε _r ) and the maximum Q × f value decrease, and the temperature coefficient of resonant frequency (τ _f ) shift to a negative value. The specimens with 3 wt%Li₂O–B₂O₃ sintered at 900 °C for 2 h showed ε _r of 8.84, Q × f value of 15,500 GHz, and τ _f of 17.8 ppm/°C. And the material was compatible with Ag electrodes, which made it a promising ceramic for low temperature co-fired ceramics technology application.