Crystals

Research

11 pages, 3719 KiB

Open AccessArticle

The Structure and Microwave Dielectric Properties of MgTi_1−x(Mn_1/3Nb_2/3)_xO₃ Ceramics

by Huan Huang, Baoyang Li, Fanshuo Wang, Yuanming Lai and Gang Jiang

Crystals 2023, 13(7), 1050; https://doi.org/10.3390/cryst13071050 - 2 Jul 2023

Cited by 8 | Viewed by 1324

MgTi_1−x(Mn_1/3Nb_2/3)_xO₃ (x = 0–0.30) ceramics were prepared via the solid-state reaction method. The phase composition, microstructure, bond characteristics, and microwave dielectric properties of MgTi_1−x(Mn_1/3Nb_2/3)_x [...] Read more.

MgTi_1−x(Mn_1/3Nb_2/3)_xO₃ (x = 0–0.30) ceramics were prepared via the solid-state reaction method. The phase composition, microstructure, bond characteristics, and microwave dielectric properties of MgTi_1−x(Mn_1/3Nb_2/3)_xO₃ (x = 0–0.30) were systematically investigated. The MgTi_1−x(Mn_1/3Nb_2/3)_xO₃ ceramics presented an ilmenite type with an R-3 space group, and the secondary-phase MgTi₂O₅ only existed at x = 0 and 0.30. The introduction of (Mn_1/3Nb_2/3)⁴⁺ effectively suppressed the formation of the MgTi₂O₅ phase. The variation trend of the dielectric constant (ε_r) was the same as relative density. The quality factor (Qf) value was enhanced by the stable microstructure, which was caused via the lattice energy of Ti/(Mn_1/3Nb_2/3)-O bonds. And a high Qf value (353,000 GHz) was obtained for MgTi_1−x(Mn_1/3Nb_2/3)_xO₃ (x = 0.04) ceramics sintered at 1250 °C. In addition, the introduction of Mn²⁺ ions with a larger ionic radius exacerbates the distortion of TiO₆ octahedra, leading to significant fluctuations in the temperature coefficient of the resonance frequency (τ_f) value. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

11 pages, 4689 KiB

Open AccessArticle

Phase Compositions and Microwave Dielectric Properties of Na_1+xSrB₅O_9+0.5x Ceramics

by Xuepeng Lu, Peng Wu, Huimin Yang, Min Yang and Yong Zheng

Crystals 2023, 13(7), 1042; https://doi.org/10.3390/cryst13071042 - 30 Jun 2023

Viewed by 1077

Abstract

Microwave dielectric ceramics composed of Na_1+xSrB₅O_9+0.5x (0 ≤ x ≤ 0.125) were synthesized via a traditional solid-state reaction approach. The effects of non-stoichiometric Na on the crystal structures, phase compositions, chemical bond characteristics, and microwave dielectric properties of [...] Read more.

Microwave dielectric ceramics composed of Na_1+xSrB₅O_9+0.5x (0 ≤ x ≤ 0.125) were synthesized via a traditional solid-state reaction approach. The effects of non-stoichiometric Na on the crystal structures, phase compositions, chemical bond characteristics, and microwave dielectric properties of the Na_1+xSrB₅O_9+0.5x ceramics were systematically studied. All Na_1+xSrB₅O_9+0.5x ceramics sintered at optimum temperatures consisted of a NaSrB₅O₉ solid-solution phase and a SrB₂O₄ phase. Appropriate excess Na could suppress the generation of the SrB₂O₄ phase, and the lowest content of the SrB₂O₄ phase was achieved at x = 0.075. The ε_r values of the Na_1+xSrB₅O_9+0.5x ceramics were primarily affected by the relative density and molecular polarization. The Q × f values showed a positive correlation with the lattice energy. The τ_f value was correlated to the SrB₂O₄ phase content, bond valence, and bond energy. Typically, the Na_1.075SrB₅O_9.0375 ceramic sintered at 825 °C possessed good microwave dielectric properties of ε_r = 5.61, Q × f = 31, 937 GHz, and τ_f = −3.09 ppm/°C, which are suitable for high-frequency, low-temperature co-fired ceramics (LTCCs) substrate applications. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

13 pages, 4713 KiB

Open AccessArticle

Effects of LiF-Addition on Sintering Behavior and Dielectric Response of LaPO₄ Ceramics at Microwave and Terahertz Frequency for LTCC Applications

by Hu Li, Dongfeng Wang, Kainan Zhang, Weijia Guo, Xiaoyu Xu, Yanbin Zhang, Yan Sun, Xingqi Xu, Jialun Du, Haitao Wu, Guangbin Duan and Zhenxing Yue

Crystals 2023, 13(7), 1035; https://doi.org/10.3390/cryst13071035 - 29 Jun 2023

Viewed by 1325

Abstract

This paper reports on the successful preparation of LaPO₄-x wt.% LiF (x = 0–5) ceramics using the traditional solid-state reaction method. The crystal structures, sintering behaviors, and dielectric response at microwave and terahertz frequencies were investigated. XRD results indicate [...] Read more.

This paper reports on the successful preparation of LaPO₄-x wt.% LiF (x = 0–5) ceramics using the traditional solid-state reaction method. The crystal structures, sintering behaviors, and dielectric response at microwave and terahertz frequencies were investigated. XRD results indicate that all the diffraction peaks were attributed to LaPO₄, and no secondary phase was observed. Rietveld refinement was conducted to analyze the variation of the crystal structure of LaPO₄-x wt.% LiF. SEM indicates that the addition of LiF significantly decreased the grain size while increasing the apparent density of the ceramics. When x = 3, the optimum microwave dielectric properties ε_r = 10.03, Q × f = 81,467 GHz, and τ_f = −43.79 ppm/°C were achieved in LaPO₄-3 wt.% LiF ceramic at 750 °C. The infrared reflectance spectrum and terahertz time-domain spectroscopy were analyzed and compared with the dielectric properties measured at microwave frequency to investigate the inherent dielectric response. The findings indicate that the dielectric constant attributed to ionic displacement polarization and oxygen vacancy is an essential factor affecting dielectric loss. Moreover, it is worth noting that the LaPO₄-3 wt.% LiF ceramic demonstrates excellent compatibility with silver powders, suggesting its immense potential as a dielectric material in LTCC applications. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

14 pages, 3841 KiB

Open AccessArticle

Photoluminescence and Temperature Sensing Properties of Bi³⁺/Sm³⁺ Co-Doped La₂MgSnO₆ Phosphor for Optical Thermometer

by Qingliang Xu, Wanqing Qian, Raz Muhammad, Xinhua Chen, Xueqing Yu and Kaixin Song

Crystals 2023, 13(7), 991; https://doi.org/10.3390/cryst13070991 - 21 Jun 2023

Cited by 6 | Viewed by 1438

Abstract

The optical temperature sensor utilizing the fluorescence intensity ratio (FIR) has garnered significant attention in the past few years due to its rapid response, robust anti-interference capability, remote control feature, and other advantages. In this study, the high-temperature solid-phase approach was used to [...] Read more.

The optical temperature sensor utilizing the fluorescence intensity ratio (FIR) has garnered significant attention in the past few years due to its rapid response, robust anti-interference capability, remote control feature, and other advantages. In this study, the high-temperature solid-phase approach was used to fabricate a variety of double perovskite-structured La₂MgSnO₆: Bi³⁺, Sm³⁺ (LMS: Bi³⁺, Sm³⁺) phosphors. The Rietveld refinement data of XRD and the Gaussian fitting of the emission peak of LMS: 0.02Bi³⁺ phosphor indicated Bi³⁺ occupies three lattice sites. The calculation and analysis of average lifetime and energy transfer efficiency substantiated the presence of energy transfer from Bi³⁺ to Sm³⁺, with a transfer efficiency of up to 59.07%. The emission intensity of LMS: 0.02Bi³⁺, 0.05Sm³⁺ at 403 K maintains 50.2% at the condition of room temperature. The FIR fitting and calculation demonstrated that LMS: 0.02Bi³⁺, 0.05Sm³⁺ phosphor possessed good optical temperature sensitivity, with a maximum absolute sensitivity S_a-max of 0.0055 K⁻¹ and a maximum relative sensitivity S_r-max of 0.88% K⁻¹, demonstrating its valuable potential applications for optical temperature sensors. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

15 pages, 6688 KiB

Open AccessArticle

Phase Structures and Dielectric Properties of (n + 1)SrO − nCeO₂ (n = 2) Microwave Ceramic Systems with TiO₂ Addition

by Qi Su, Jingjing Qu, Fei Liu, Changlai Yuan, Xiao Liu, Mingwei Su, Liufang Meng and Guohua Chen

Crystals 2023, 13(6), 955; https://doi.org/10.3390/cryst13060955 - 15 Jun 2023

Viewed by 1255

Abstract

Ti⁴⁺-ion-doped (n + 1)SrO − nCeO₂ (n = 2) ceramic systems were prepared with the conventional solid-state reaction method, and the effects of the phase structures and compositions, sintering behaviors, microstructures and microwave dielectric properties of these [...] Read more.

Ti⁴⁺-ion-doped (n + 1)SrO − nCeO₂ (n = 2) ceramic systems were prepared with the conventional solid-state reaction method, and the effects of the phase structures and compositions, sintering behaviors, microstructures and microwave dielectric properties of these ceramic systems were investigated in detail as a function of TiO₂ content. The analytical results of the XRD patterns show that the pure (n + 1)SrO − nCeO₂ (n = 2) system is a composite-phase ceramic system with coexisting SrCeO₃ and Sr₂CeO₄ phases (represented as a SrCeO₃ + Sr₂CeO₄ system), which belong to the orthogonal structures of the Pmcn (62) and Pbam (55) space groups, respectively. For the xTiO₂-(1 − x) (SrCeO₃ + Sr₂CeO₄) (x = 0.1–0.4) ceramic samples, the secondary phase Sr₂TiO₄ can also be detected within the range of the investigated components. Meanwhile, the Raman spectroscopy, SEM-EDS, and HRTEM (SAED) analysis results also verified the correctness and consistency of the phase structures and compositions for all the given specimens. In addition, complex impedance spectroscopy was used to detect the conductive behavior of these compound ceramic systems, and the calculation results show that the appropriate addition of Ti⁴⁺-ions can make the SrCeO₃ + Sr₂CeO₄ system have better thermal stability. The composition of x = 0.2 multiphase structural ceramic sample sintered at 1330 °C for 4 h has a near zero τ_f value of ~−4.6 ppm/°C, a moderate ε_r of ~40.3 and a higher Q × f~44,020 GHz (at 6.56 GHz). The relatively superior-performing ceramics developed in this work are expected to provide a promising microwave dielectric material for communication components. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

8 pages, 6333 KiB

Open AccessArticle

Microwave Dielectric Properties of Li₃TiO₃F Oxyfluorides Ceramics

by Guoguang Yao, Jiuyan Zhao, Ya Lu, Hongkai Liu, Cuijin Pei, Qian Ding, Miao Chen, Yaming Zhang, Ding Li and Fu Wang

Crystals 2023, 13(6), 897; https://doi.org/10.3390/cryst13060897 - 31 May 2023

Cited by 14 | Viewed by 1623

Abstract

Using a solid-state reaction strategy, nominal Li₃TiO₃F oxyfluorides ceramics were fabricated, and its sintering behavior, microstructure, phase assemblages, as well as microwave dielectric performances were all investigated. The main phase of Li₃TiO₃F with cubic structures [...] Read more.

Using a solid-state reaction strategy, nominal Li₃TiO₃F oxyfluorides ceramics were fabricated, and its sintering behavior, microstructure, phase assemblages, as well as microwave dielectric performances were all investigated. The main phase of Li₃TiO₃F with cubic structures accompanied with small amounts of the LiF or Li₂TiO₃ secondary phase was identified by XRD analysis. SEM analysis showed that a uniform and dense microstructure was obtained for 750 °C-sintered samples. The dielectric constant (ε_r) and quality factor (Q × f) were found to be strongly correlated with porosity and grain size distribution, whereas the temperature coefficient of resonance frequency (τ_f) was mainly dominated by the phase assemblages. In particular, the 750 °C-sintered Li₃TiO₃F samples exhibited good microwave dielectric performances: ε_r = 18, Q × f = 57,300 GHz (under 9.2 GHz), τ_f = −43.0 ppm/°C. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

8 pages, 5334 KiB

Open AccessArticle

Microwave Dielectric Properties of CaB₂O₄-CaSiO₃ System for LTCC Applications

by Changzhi Yin, Zhengyu Zou, Mingfei Cheng, Yiyang Cai, Jiaqing Yang, Weicheng Lei, Wenzhong Lu, Xiaoqiang Song and Wen Lei

Crystals 2023, 13(5), 790; https://doi.org/10.3390/cryst13050790 - 9 May 2023

Cited by 6 | Viewed by 2020

Abstract

A novel composite ceramic with low densification temperature was fabricated using the conventional solid-state method. The XRD and Rietveld refinement results indicated that the two phases of CaB₂O₄ and CaSiO₃ can coexist in all compositions. Furthermore, a phase transition [...] Read more.

A novel composite ceramic with low densification temperature was fabricated using the conventional solid-state method. The XRD and Rietveld refinement results indicated that the two phases of CaB₂O₄ and CaSiO₃ can coexist in all compositions. Furthermore, a phase transition of CaSiO₃ ceramic from α-phase to β-phase was observed. A dense ceramic with excellent microwave dielectric properties (ε_r~6.4, Q × f~75,600 GHz, and a negative τ_f~26.9 ppm/°C) was obtained at x = 0.5 when sintered at 925 °C at the frequency of 14.2 GHz. A good chemical compatibility between the composite ceramic and Ag electrode was improved by elemental mapping results. A patch antenna was fabricated based on the simulated result. All results indicated that the 0.5 CaB₂O₄ + 0.5 CaSiO₃ ceramic has large application potential in the LTCC field. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

11 pages, 5761 KiB

Open AccessArticle

The Influence of CaF₂ Doping on the Sintering Behavior and Microwave Dielectric Properties of CaO-B₂O₃-SiO₂ Glass-Ceramics for LTCC Applications

by Chao Dong, Hua Wang, Tingnan Yan, Jianwei Zhao, Jiwen Xu and Dawei Wang

Crystals 2023, 13(5), 748; https://doi.org/10.3390/cryst13050748 - 30 Apr 2023

Cited by 12 | Viewed by 1987

Abstract

With the rapid development of microelectronic information technology, microelectronic packaging has higher requirements in terms of integration density, signal transmission speed, and passive component integration. Low temperature co-fired ceramics (LTCC) exhibit excellent dielectric properties and low temperature sintering properties, which meets the above-mentioned [...] Read more.

With the rapid development of microelectronic information technology, microelectronic packaging has higher requirements in terms of integration density, signal transmission speed, and passive component integration. Low temperature co-fired ceramics (LTCC) exhibit excellent dielectric properties and low temperature sintering properties, which meets the above-mentioned requirements. This work investigates the effects of CaF₂ doping (0–16 mol%) on the glass structure, sintering behavior, crystallization, microstructure, and microwave dielectric properties of the CaO-B₂O₃-SiO₂ (CBS) glass-ceramic system. Glass-ceramics were prepared using the conventional melting and quenching method. The physical and chemical properties of the glass-ceramics were analyzed using various techniques including TMA, SDT, FTIR, XRD, SEM, and a network analyzer. The results indicate that CaF₂ doping can effectively reduce the sintering temperature and softening temperature of CBS ceramics. It also substantially improves the densification, dielectric, and mechanical properties. The appropriate amount of CaF₂-doped CBS glass-ceramics can be sintered below 800 °C with a low dielectric constant and loss at high frequency (ε_r < 6, tanδ < 0.02 @ 10~13 GHz). Specifically, 8 mol% CaF₂ doped CBS glass-ceramics sintered at 790 °C exhibit excellent microwave dielectric and thermal properties, with ε_r ~ 5.92 @ 11.4 GHz, tanδ ~ 1.59 × 10⁻³, CTE ~ 7.76 × 10⁻⁶/°C, λ ~ 2.17 W/(m·k), which are attractive for LTCC applications. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

10 pages, 4727 KiB

Open AccessArticle

Sintering Characteristics and Microwave Dielectric Properties of BaTi₄O₉ Ceramics with CuO–TiO₂ Addition

by Haoxuan Guo, Peishu Zhu, Qingping Lin, Min Gao, Deping Tang and Xinghua Zheng

Crystals 2023, 13(4), 566; https://doi.org/10.3390/cryst13040566 - 27 Mar 2023

Cited by 4 | Viewed by 1617

Abstract

Sintering characteristics, phase evolutions, microstructures, and microwave dielectric properties have been investigated for BaTi₄O₉ ceramics prepared by traditional low temperature sintering using CuO–TiO₂ (CT) additions as aids. The sintering temperature of BaTi₄O₉ ceramics was found to [...] Read more.

Sintering characteristics, phase evolutions, microstructures, and microwave dielectric properties have been investigated for BaTi₄O₉ ceramics prepared by traditional low temperature sintering using CuO–TiO₂ (CT) additions as aids. The sintering temperature of BaTi₄O₉ ceramics was found to evidently reduce from 1350 °C to about 1100 °C with a very small amount of 0.5 wt% CT addition. When the CT addition increased to beyond 0.5 wt%, however, it was not expected to further lower the sintering temperature. Meantime, the secondary phases of Ba₄Ti₁₃O₃₀, BaTiO₃, and TiO₂ were observed in these BaTi₄O₉-based ceramics when the CT content was beyond 2 wt%. With the introduction of the CT addition, the permittivity (ε) had little enhancement, and the temperature coefficient of the resonant frequency (τ_f) was improved to near zero. The BaTi₄O₉ ceramics with 0.5 wt% CT additions, sintered at 1100 °C, exhibited excellent microwave dielectric properties, such as ε = 36.9, Q × f = 23100 GHz, and τ_f = 2.5 ppm/°C. In addition, the densification mechanism and variations of the microwave dielectric properties have also been discussed with the crystal phase and microstructure’s evolution. Full article

(This article belongs to the Special Issue Microwave Dielectric Ceramics)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Microwave Dielectric Ceramics

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Benefits of Publishing in a Special Issue

Published Papers (9 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI