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12 pages, 4248 KiB

Open AccessArticle

Immittance Studies of Bi₆Fe₂Ti₃O₁₈ Ceramics

by Agata Lisińska-Czekaj, Dionizy Czekaj, Barbara Garbarz-Glos and Wojciech Bąk

Materials 2020, 13(22), 5286; https://doi.org/10.3390/ma13225286 - 22 Nov 2020

Cited by 6 | Viewed by 1897

Results of studies focusing on the electric behavior of Bi₆Fe₂Ti₃O₁₈ (BFTO) ceramics are reported. BFTO ceramics were fabricated by solid state reaction methods. The simple oxides Bi₂O₃, TiO₂, and Fe [...] Read more.

Results of studies focusing on the electric behavior of Bi₆Fe₂Ti₃O₁₈ (BFTO) ceramics are reported. BFTO ceramics were fabricated by solid state reaction methods. The simple oxides Bi₂O₃, TiO₂, and Fe₂O₃ were used as starting materials. Immittance spectroscopy was chosen as a method to characterize electric and dielectric properties of polycrystalline ceramics. The experimental data were measured in the frequency range Δν = (10⁻¹–10⁷) Hz and the temperature range ΔT = (−120–200) °C. Analysis of immittance data was performed in terms of complex impedance, electric modulus function, and conductivity. The activation energy corresponding to a non-Debye type of relaxation was found to be E_A = 0.573 eV, whereas the activation energy of conductivity relaxation frequency was found to be E_A = 0.570 eV. An assumption of a hopping conductivity mechanism for BFTO ceramics was studied by ‘universal’ Jonscher’s law. A value of the exponents was found to be within the “Jonscher’s range” (0.54 ≤ n ≤ 0.72). The dc-conductivity was extracted from the measurements. Activation energy for dc-conductivity was calculated to be E_DC = 0.78 eV, whereas the dc hopping activation energy was found to be E_H = 0.63 eV. The obtained results were discussed in terms of the jump relaxation model. Full article

(This article belongs to the Special Issue Electroceramic Materials)

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13 pages, 5054 KiB

Open AccessArticle

Chemical and Physical Properties of the BLT4 Ultra Capacitor—A Suitable Material for Ultracapacitors

by B. Wodecka-Duś, M. Adamczyk-Habrajska, T. Goryczka and D. Bochenek

Materials 2020, 13(3), 659; https://doi.org/10.3390/ma13030659 - 2 Feb 2020

Cited by 7 | Viewed by 2433 | Correction

Abstract

This paper describes the properties of a lead-free ceramic material based on barium titanate, designed for the construction of ultracapacitors and sensors used in mechatronic systems. The admixture of lanthanum (La³⁺) served as a modifier. The ceramic powders were obtained by [...] Read more.

This paper describes the properties of a lead-free ceramic material based on barium titanate, designed for the construction of ultracapacitors and sensors used in mechatronic systems. The admixture of lanthanum (La³⁺) served as a modifier. The ceramic powders were obtained by the solid phase reaction method (conventional method—mixed oxides method—MOM). Technological conditions of the synthesis process were determined on the basis of thermal analysis. The obtained samples are characterized, at room temperature (T_r < T_C), by a single-phase tetragonal structure and a P4mm space group. Properly developed large grains (d = 5 µm) contributed to the increase in electric permittivity, the maximum value of which is at the level of ε_m ≈ 112,000, as well as to a strong decrease in specific resistance in the ferroelectric phase, whereas above the Curie temperature, by creating a potential barrier at their boundaries, there was a a rapid increase in resistivity. The temperature coefficient of resistance of the obtained posistor is 10.53%/K. The electrical properties of the obtained ceramics were examined using impedance spectroscopy. In order to analyze the obtained results, a method of comparing the behavior of the real object and its replacement system in a specific frequency region was used, whereas the Kramer–-Kroning (K–K) test was used to determine the consistency of the measured data. The proper selection of the stoichiometry and synthesis conditions resulted in the creation of an appropriate concentration of donor levels and oxygen gaps, which in turn resulted in a significant increase in the value of electrical permittivity, with small values of the angle of dielectric loss tangent. This fact predisposes the discussed material for certain applications (in the construction of ultracapacitors, among others). Full article

(This article belongs to the Special Issue Electroceramic Materials)

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12 pages, 6519 KiB

Open AccessArticle

Preparation and Dielectric Properties of K_1/2Na_1/2NbO₃ Ceramics Obtained from Mechanically Activated Powders

by Izabela Szafraniak-Wiza, Jolanta Dzik, Dariusz Bochenek, Diana Szalbot and Małgorzata Adamczyk-Habrajska

Materials 2020, 13(2), 401; https://doi.org/10.3390/ma13020401 - 15 Jan 2020

Cited by 4 | Viewed by 2371

Abstract

Alkaline based materials have been considered as a replacement for environmentally harmful Pb(Zr,Ti)O₃ (PZT) electro-ceramics. In this paper, the K_1/2Na_1/2NbO₃ (KNN) ceramics were prepared in a three stage process: first Nb₂O₅, Na₂ [...] Read more.

Alkaline based materials have been considered as a replacement for environmentally harmful Pb(Zr,Ti)O₃ (PZT) electro-ceramics. In this paper, the K_1/2Na_1/2NbO₃ (KNN) ceramics were prepared in a three stage process: first Nb₂O₅, Na₂CO_3, and K₂CO₃ were milled in a high energy mill (shaker type) for different periods, between 25 h and 100 h, consecutively a solid state reaction was carried out at 550 °C. Finally, the uniaxially pressed samples were sintered at 1000 °C. The reaction temperature is lower for mechanically activated powders than in the case of the conventional solid-state method. The ceramic samples, prepared from the mechanically activated powders, were investigated by dielectric spectroscopy. The influence of the duration of the mechanical activation on the properties of the ceramic materials, e.g., ceramic microstructures, phase transition temperatures, character of the temperature dependences of dielectric permittivity, are discussed. Full article

(This article belongs to the Special Issue Electroceramic Materials)

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12 pages, 2679 KiB

Open AccessArticle

Sintering Behaviors, Microstructure, and Microwave Dielectric Properties of CaTiO₃–LaAlO₃ Ceramics Using CuO/B₂O₃ Additions

by Min-Hang Weng, Chihng-Tsung Liauh, Shueei-Muh Lin, Hung-Hsiang Wang and Ru-Yuan Yang

Materials 2019, 12(24), 4187; https://doi.org/10.3390/ma12244187 - 13 Dec 2019

Cited by 17 | Viewed by 2941

Abstract

The effect of CuO/B₂O₃ additions on the sintering behaviors, microstructures, and microwave dielectric properties of 0.95LaAlO₃–0.05CaTiO₃ ceramics is investigated. It is found that the sintering temperatures are lowered efficiently from 1600 °C to 1350 °C, as 1 [...] Read more.

The effect of CuO/B₂O₃ additions on the sintering behaviors, microstructures, and microwave dielectric properties of 0.95LaAlO₃–0.05CaTiO₃ ceramics is investigated. It is found that the sintering temperatures are lowered efficiently from 1600 °C to 1350 °C, as 1 wt % CuO, 1 wt % B₂O₃, and 0.5 wt % CuO +0.5 wt % B₂O₃ are used as the sintering aids due to the appearance of the liquid phase sintering. The microwave dielectric properties of 0.95LaAlO₃–0.05CaTiO₃ ceramics with the sintering aid additions are strongly related to the densification and the microstructure of the sintered ceramics. At the sintering temperature of 1300 °C, the 0.95LaAlO₃–0.05CaTiO₃ ceramic with 0.5 wt % CuO + 0.5 wt % B₂O₃ addition shows the best dielectric properties, including a dielectric constant (ε_r) of 21, approximate quality factor (Q × f) of 22,500 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −3 ppm/°C. Full article

(This article belongs to the Special Issue Electroceramic Materials)

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12 pages, 5411 KiB

Open AccessArticle

Comparison of Electrophysical Properties of PZT-Type Ceramics Obtained by Conventional and Mechanochemical Methods

by Dariusz Bochenek, Przemysław Niemiec, Izabela Szafraniak-Wiza and Grzegorz Dercz

Materials 2019, 12(20), 3301; https://doi.org/10.3390/ma12203301 - 11 Oct 2019

Cited by 7 | Viewed by 2402

Abstract

In the paper, the multicomponent PZT-type ceramics with Pb(Zr_0.49Ti_0.51)_0.94Mn_0.015Sb_0.01W_0.015Ni_0.03O₃ composition have been obtained by conventional and mechanochemical methods. With conventional ceramic technology, PZT-type ceramics have been synthesized by [...] Read more.

In the paper, the multicomponent PZT-type ceramics with Pb(Zr_0.49Ti_0.51)_0.94Mn_0.015Sb_0.01W_0.015Ni_0.03O₃ composition have been obtained by conventional and mechanochemical methods. With conventional ceramic technology, PZT-type ceramics have been synthesized by the method of calcination powder (850 °C/4 h). Instead of this step, the mechanochemical synthesis process for different milling periods (15 h, 25 h, 50 h, 75 h) has been applied for a second batch of samples. To obtain the dense PZT-type ceramic samples, powders have been sintered by free sintering method at conditions of 1150 °C/2 h. Studies have shown that the perovskite structure of the PZT-type material is formed during mechanochemical activation of powders during the technological process at low temperature. The application of the mechanochemical synthesis to obtain the PZT-type materials also allows shortening of the technological process, and the useful electrophysical properties of ceramic samples are not reduced at the same time. The presented results have confirmed that the investigated materials can be used in microelectronic applications, especially as elements of actuators and piezoelectric transducers. Full article

(This article belongs to the Special Issue Electroceramic Materials)

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10 pages, 2235 KiB

Open AccessFeature PaperArticle

Temperature Stable Cold Sintered (Bi_0.95Li_0.05)(V_0.9Mo_0.1)O₄-Na₂Mo₂O₇ Microwave Dielectric Composites

by Dawei Wang, Shiyu Zhang, Di Zhou, Kaixin Song, Antonio Feteira, Yiannis Vardaxoglou, Will Whittow, Darren Cadman and Ian M. Reaney

Materials 2019, 12(9), 1370; https://doi.org/10.3390/ma12091370 - 27 Apr 2019

Cited by 49 | Viewed by 4886

Abstract

Dense (Bi_0.95Li_0.05)(V_0.9Mo_0.1)O₄-Na₂Mo₂O₇ (100−x) wt.% (Bi_0.95Li_0.05)(V_0.9Mo_0.1)O₄ (BLVMO)-x wt.% Na₂Mo₂O₇ (NMO) composite ceramics were successfully fabricated [...] Read more.

Dense (Bi_0.95Li_0.05)(V_0.9Mo_0.1)O₄-Na₂Mo₂O₇ (100−x) wt.% (Bi_0.95Li_0.05)(V_0.9Mo_0.1)O₄ (BLVMO)-x wt.% Na₂Mo₂O₇ (NMO) composite ceramics were successfully fabricated through cold sintering at 150 °C under at 200 MPa for 30 min. X-ray diffraction, back-scattered scanning electron microscopy, and Raman spectroscopy not only corroborated the coexistence of BLVMO and NMO phases in all samples, but also the absence of parasitic phases and interdiffusion. With increasing NMO concentration, the relative pemittivity (ε_r) and the Temperature Coefficient of resonant Frequency (TCF) decreased, whereas the Microwave Quality Factor (Qf) increased. Near-zero TCF was measured for BLVMO-20wt.%NMO composites which exhibited ε_r ~ 40 and Qf ~ 4000 GHz. Finally, a dielectric Graded Radial INdex (GRIN) lens was simulated using the range of ε_r in the BLVMO-NMO system, which predicted a 70% aperture efficiency at 26 GHz, ideal for 5G applications. Full article

(This article belongs to the Special Issue Electroceramic Materials)

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7 pages, 2586 KiB

Open AccessArticle

Intentional Carrier Doping to Realize n-Type Conduction in Zintl Phases Eu_5−yLa_yIn_2.2Sb₆

by Jianwei Lin, Wanyu Lv, Yayun Gu, Kai Guo, Xinxin Yang and Jingtai Zhao

Materials 2019, 12(2), 264; https://doi.org/10.3390/ma12020264 - 15 Jan 2019

Cited by 6 | Viewed by 2742

Abstract

Due to the tunable electrical transport properties and lower thermal conductivity, Zintl phase compounds have been considered as a promising candidate for thermoelectric applications. Most Sb-based Zintl compounds exhibit essentially p-type conduction as result of the cation vacancy. Herein, n-type Zintl [...] Read more.

Due to the tunable electrical transport properties and lower thermal conductivity, Zintl phase compounds have been considered as a promising candidate for thermoelectric applications. Most Sb-based Zintl compounds exhibit essentially p-type conduction as result of the cation vacancy. Herein, n-type Zintl phases Eu_5−yLa_yIn_2.2Sb₆ has been successfully synthesized via controlling the vacancy defect combined with intentional electron doping. Excess of In would occupy the vacancy while La doping enables the electron to be the major carrier at the measured temperate range, realizing the n-type conduction for Eu_5−yLa_yIn_2.2Sb₆ (y ≥ 0.04). Meanwhile, the thermal conductivity of Eu_5−yLa_yIn_2.2Sb₆ reduces from 0.90 W/mK to 0.72 W/mK at 583 K derived from the La doping-induced disorder. The maximum thermoelectric figure of merit zT = 0.13 was obtained. This work firstly realizes the n-type conduction in Eu₅In₂Sb₆, which sheds light on the strategy to synthesize n-type Zintl thermoelectric materials and promotes the practical applications of Zintl thermoelectric devices. Full article

(This article belongs to the Special Issue Electroceramic Materials)

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16 pages, 3843 KiB

Open AccessArticle

Electric Current Dependent Fracture in GaN Piezoelectric Semiconductor Ceramics

by Guoshuai Qin, Chunsheng Lu, Xin Zhang and Minghao Zhao

Materials 2018, 11(10), 2000; https://doi.org/10.3390/ma11102000 - 16 Oct 2018

Cited by 25 | Viewed by 3185

Abstract

In this paper, the fracture behavior of GaN piezoelectric semiconductor ceramics was investigated under combined mechanical and electric loading by using three-point bending tests and numerical analysis. The experimental results demonstrate that, in contrast to traditional insulating piezoelectric ceramics, electric current is a [...] Read more.

In this paper, the fracture behavior of GaN piezoelectric semiconductor ceramics was investigated under combined mechanical and electric loading by using three-point bending tests and numerical analysis. The experimental results demonstrate that, in contrast to traditional insulating piezoelectric ceramics, electric current is a key factor in affecting the fracture characteristics of GaN ceramics. The stress, electric displacement, and electric current intensity factors were numerically calculated and then a set of empirical formulae was obtained. By fitting the experimental data, a fracture criterion under combined mechanical and electrical loading was obtained in the form of an ellipsoid function of intensity factors. Such a fracture criterion can be extended to predict the failure behavior of other piezoelectric semiconductors or devices with a crack, which are useful in their reliability design and applications. Full article

(This article belongs to the Special Issue Electroceramic Materials)

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14 pages, 6016 KiB

Open AccessArticle

Reliability of X7R Multilayer Ceramic Capacitors During High Accelerated Life Testing (HALT)

by Ana María Hernández-López, Juan Antonio Aguilar-Garib, Sophie Guillemet-Fritsch, Roman Nava-Quintero, Pascal Dufour, Christophe Tenailleau, Bernard Durand and Zarel Valdez-Nava

Materials 2018, 11(10), 1900; https://doi.org/10.3390/ma11101900 - 4 Oct 2018

Cited by 19 | Viewed by 7361

Abstract

Multilayer ceramic capacitors (MLCC) are essential components for determining the reliability of electronic components in terms of time to failure. It is known that the reliability of MLCCs depends on their composition, processing, and operating conditions. In this present work, we analyzed the [...] Read more.

Multilayer ceramic capacitors (MLCC) are essential components for determining the reliability of electronic components in terms of time to failure. It is known that the reliability of MLCCs depends on their composition, processing, and operating conditions. In this present work, we analyzed the lifetime of three similar X7R type MLCCs based on BaTiO₃ by conducting High Accelerated Life Tests (HALT) at temperatures up to 200 °C at 400 V and 600 V. The results were adjusted to an Arrhenius equation, which is a function of the activation energy (E_a) and a voltage stress exponent (n), in order to predict their time to failure. The values of E_a are in the range of 1–1.45 eV, which has been reported for the thermal failure and dielectric wear out of BaTiO₃-based dielectric capacitors. The stress voltage exponent value was in the range of 4–5. Although the E_a can be associated with a failure mechanism, n only gives an indication of the effect of voltage in the tests. It was possible to associate those values with each type of tested MLCC so that their expected life could be estimated in the range of 400–600 V. Full article

(This article belongs to the Special Issue Electroceramic Materials)

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