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Lead-free Ferro-/Piezoelectric Ceramics and Thin Films

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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Polycrystalline Ceramics".

Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 27535

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Special Issue Editors

Dr. Jinyan Zhao

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Guest Editor

School of Electronic Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Interests: lead-free piezo-/ferroelectric ceramics; thin films; and devices

Dr. Zenghui Liu

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Guest Editor

School of Electronic Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Interests: piezoelectric/ferroelectric materials and devices; structure–property relations in solid-state functional materials
Special Issues, Collections and Topics in MDPI journals

Dr. Ting Zheng

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Guest Editor

School of Materials Science and Engineering, Sichuan University, Chengdu 610065, China
Interests: lead-free piezo/ferroelectric materials

Special Issue Information

Dear Colleagues,

Piezoelectrics are an important class of function materials that convert mechanical energy into electrical energy, and vice versa. Ferroelectrics are a special class of piezoelectrics with switchable polarization. Ferro-/piezoelectric ceramics and thin films hold key importance both in existing and new technological applications in energy storage, energy harvesting, sensors, actuators, electromechanical transducers, and micro-and nano-electromechanical systems (MEMS/NEMS), which are the building blocks of future-generation smart electronics, robotics, and the Internet of Things (IoT). With increasing concerns about the environmental and health problems in traditional lead-based ferro-/piezoelectric materials (such as lead zirconate titanate, PZT), it is imperative to develop environmentally friendly “lead-free ferro-/piezoelectric” alternatives with a similar performance. However, there are still obstacles to overcome in order to realize this objective. Therefore, this Special Issue aims to encourage efforts towards this research direction, including the latest progress in the fabrication process, the high performance, the fundamental mechanisms, the novel structural strategies, and the relationship between the structures and macroscopic properties of lead-free ferro-/piezoelectric ceramics and thin films. Research on state-of-the-art piezo-/ferroelectrics devices, namely, nanogenerators, memorizers, sensors, and transducers, is also encouraged. These materials include both inorganic (e.g., perovskite and bismuth layer-structured ferro-/piezoelectric ceramics and ZnO nanostructures) and organic (e.g., polyvinylidene difluoride (PVDF) and its copolymers and their composites, and biopolymers) lead-free ferro-/piezoelectric materials.

Dr. Jinyan Zhao
Dr. Zenghui Liu
Dr. Ting Zheng
Guest Editors

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Keywords

perovskite
bismuth layer-structured
polymers
structure
domain structure
devices
lead-free
ferro-/piezoelectrics

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Published Papers (14 papers)

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10 pages, 3532 KiB

Open AccessArticle

Negative Thermal Expansion Caused by the Antiferroelectric Phase Transition in Lead-Free Perovskite Ceramics

by Huifen Yu, Liang Chen, Chang Zhou and He Qi

Crystals 2023, 13(5), 751; https://doi.org/10.3390/cryst13050751 - 1 May 2023

Cited by 2 | Viewed by 1823

Abstract

Due to the structural stability and high adjustability of perovskite, lead-free perovskite ceramics are widely thought to be one of the most promising functional materials. In this work, an abnormal negative thermal expansion behavior with a linear expansion coefficient of −54.95 ppm/K is achieved in the (1-x)NaNbO₃-xCaZrO₃ system by driving the antiferroelectric phase transition from orthorhombic phase and tetragonal phase. The NTE mechanism is verified by temperature-dependent high-energy synchrotron X-ray diffraction, dielectric spectra, and Raman scattering spectroscopy. The relationship between the antiferroelectric phase transition and negative thermal expansion behavior is systematically revealed by analyzing the evolution of the phase structure with temperature. This novel negative thermal expansion feature caused by the antiferroelectric phase transition provides new guidance for designing more negative thermal expansion materials. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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13 pages, 15354 KiB

Open AccessArticle

Tunable Phase Structure in Mn-Doped Lead-Free BaTiO₃ Crystalline/Amorphous Energy Storage Thin Films

by Jianlu Geng, Dongxu Li, Hua Hao, Qinghu Guo, Huihuang Xu, Minghe Cao, Zhonghua Yao and Hanxing Liu

Crystals 2023, 13(4), 649; https://doi.org/10.3390/cryst13040649 - 10 Apr 2023

Cited by 4 | Viewed by 1959

Abstract

For dielectric energy storage materials, high polarization and high breakdown strengths are a long-standing challenge. A modulating crystalline/amorphous phase structure strategy is proposed by Mn-doping and annealing temperature to enhance the energy storage performance of pure BaTiO₃ (BT) films. In this study, lead-free Mn-doped BT films were prepared on Pt/Ti/SiO₂/Si substrates via the sol-gel method, and the effects of the crystalline/amorphous phase ratio on polarization and electric properties were analyzed. A small amount of Mn-doping in BT could reduce the annealing temperature and enhance polarization with an Mn content of 8%. In addition, the energy storage properties of BT-8%Mn films achieve the best energy storage performance in terms of energy density and efficiency of 72.4 J/cm³ and 88.5% by changing the annealing temperature to 640 °C. BT-8%Mn energy storage films also possess good stability over a wide temperature range of 20 °C–200 °C, which demonstrates that crystalline/amorphous engineering is a simple and effective way to enhance energy storage applications of dielectric films. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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11 pages, 4069 KiB

Open AccessArticle

Effect of the Annealing Conditions on the Strain Responses of Lead-Free (Bi_0.5Na_0.5)TiO₃–BaZrO₃ Ferroelectric Thin Films

by Zhe Wang, Jinyan Zhao and Wei Ren

Crystals 2023, 13(4), 606; https://doi.org/10.3390/cryst13040606 - 2 Apr 2023

Cited by 1 | Viewed by 1535

Abstract

Bismuth sodium titanate (Bi_0.5Na_0.5)TiO₃ (BNT)–based thin films have attracted large attention for the production of modern precise micro–devices due to their outstanding strain responses. However, obtaining good electrical properties and low leakage current in BNT-based thin films is still a great challenge. In this work, 0.945(Bi_0.5Na_0.5)TiO₃–0.055BaZrO₃ (BNT–5.5BZ) thin films were deposited by the chemical solution deposition (CSD) method and annealed under two different conditions. This work describes a careful research study on the influence of the annealing conditions on the crystalline structure, morphology, and electrical performance of the BNT–5.5BZ thin films. The films exhibited a dense structure and excellent electrical properties following an optimized thermal treatment process. An ultra–high strain response of 1.5% with a low dielectric loss of ~0.03 was obtained in the BNT–5.5BZ thin films after post-annealing in an O₂ atmosphere. The results of this work show that the enhanced strain response was mainly due to a reversible field-induced phase transition between the ferroelectric phase and the relaxation state. The post-annealing treatment is an effective method to optimize the electrical properties of BNT–based films, providing many opportunities for the application of ferroelectric devices. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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10 pages, 3683 KiB

Open AccessArticle

The Synthesis and Domain Structures of Single-Crystal-Like Mesoscale BaTiO₃ Plates

by Kun Zheng, Jian Zhuang, Yi Quan, Jinyan Zhao, Lingyan Wang, Zhe Wang and Wei Ren

Crystals 2023, 13(3), 538; https://doi.org/10.3390/cryst13030538 - 21 Mar 2023

Cited by 4 | Viewed by 1932

Abstract

The (001) plate-like BaTiO₃ piezoelectric micromaterials are synthesized by topochemical microcrystal conversion technique. BaTiO₃ plates with a length of 2~10 μm and thickness of 0.5~1.3 μm are obtained. The dependence of morphology on synthesis conditions is discussed in detail. The crystal symmetry and multiscale domain structures of BaTiO₃ plates are systematically investigated by various characterizations. X-ray diffraction (XRD) and Raman spectra analyses demonstrate the tetragonal symmetry of the (001) oriented BaTiO₃ plates at room temperature. The domain configurations of the micron BaTiO₃ are investigated with a polarized light microscope (PLM) and piezoresponse force microscopy (PFM). The single-crystal-like quality and uniformity are supported by PLM observations. More importantly, the classical 90° banded ferroelectric domains of ~125 nm width are observed for the first time in such BaTiO₃ plates. The domain features in the mesoscale BaTiO₃ plate are discussed and compared with its bulk counterparts. The results may provide insights into understanding and designing the mesoscale BaTiO₃ functional materials. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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11 pages, 4551 KiB

Open AccessArticle

Thermoelectrical Properties of ITO/Pt, In₂O₃/Pt and ITO/In₂O₃ Thermocouples Prepared with Magnetron Sputtering

by Yantao Liu, Peng Shi, Wei Ren and Rong Huang

Crystals 2023, 13(3), 533; https://doi.org/10.3390/cryst13030533 - 20 Mar 2023

Cited by 2 | Viewed by 1842

Abstract

ITO/Pt, In₂O₃/Pt and ITO/In₂O₃ thermocouples were prepared by the radio frequency (RF) magnetron sputtering method. The XRD results showed that all the annealed ITO and In₂O₃ films annealed at high temperature present a cubic structure. Scanning electron microscope results showed that the thickness of the ITO and In₂O₃ films could reach 1.25 µm and 1.21 µm, respectively. The ITO/Pt and In₂O₃/Pt thin film thermocouples could obtain an output voltage of 68.7 mV and 183.5 mV, respectively, under a 900 °C temperature difference, and at the same time, the Seebeck coefficient reached 76.1 µV/°C and 203.9 µV/°C, respectively. For the ITO/In₂O₃ thermocouple, the maximum value of the output voltage was 165.7 mV under a 1200 °C temperature difference, and the Seebeck coefficient was 138.1 µV/°C. Annealing under different atmosphere conditions under 1000 °C, including vacuum, air and nitrogen atmospheres, resulted in values of the Seebeck coefficient that were 138.2 µV/°C, 135.5 µV/°C and 115.7 µV/°C, respectively. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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11 pages, 3184 KiB

Open AccessArticle

The Vertically Heteroepitaxial Structure for Lead-Free Piezoelectric K_0.5Na_0.5NbO₃ Films

by Zhe Wang, Lingyan Wang, Wei Ren, Chao Li, Yi Quan, Kun Zheng and Jian Zhuang

Crystals 2023, 13(3), 525; https://doi.org/10.3390/cryst13030525 - 19 Mar 2023

Cited by 1 | Viewed by 1767

Abstract

The effect of epitaxial strain on the electrical properties of ferroelectric films has been widely investigated. However, this kind of strain is generally attributed to the substrate clamping constraints and is easily relaxed when the thickness of films is over 100 nm. In this work, a vertically epitaxial strain was introduced into lead-free piezoelectric K_0.5Na_0.5NbO₃ films to improve the electrical properties of ferroelectric films. Two-phase, vertically epitaxial composite KNN-ZnO thin films were grown on the (001) STO substrate using a pulsed laser deposition (PLD) method. The highly (001) preferentially oriented KNN phase and (11

\bar{2}

0)-oriented ZnO phase were orderly arranged. Two types of morphologies of “square-like” and “stripe-looking” grains were observed in the surface image. An asymmetric “square” out-of-plane phase hysteresis loop and a “butterfly” displacement loop were exhibited in the KNN phase, whereas the ZnO phase showed a closed phase hysteresis loop and a slim displacement-voltage loop. Two different kinds of polarization behaviors for domains were also observed under applied electric fields, in which the domain of the KNN phase is easily switched to the opposite state, whereas the ZnO phase keeps a stable domain state when applying a DC bias of ±50 V. the vertically epitaxial growth of the KNN-ZnO composited films in this work provides a new way to fabricate complex nanoscale materials. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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11 pages, 4033 KiB

Open AccessArticle

Structure, Electrical Properties, and Thermal Stability of the Mn/Nb Co-Doped Aurivillius-Type Na_0.5Bi_4.5Ti₄O₁₅ High Temperature Piezoelectric Ceramics

by Tianlong Zhao, Kefei Shi, Chunlong Fei, Xinhao Sun, Yi Quan, Wen Liu, Juan Zhang and Xianying Dai

Crystals 2023, 13(3), 433; https://doi.org/10.3390/cryst13030433 - 2 Mar 2023

Cited by 6 | Viewed by 1821

Abstract

In order to meet the urgent need for high temperature piezoelectric materials with a Curie temperature over 400 °C, the Mn/Nb co-doped strategy has been proposed to improve the weak piezoelectric performance of the Aurivillius-type Na_0.5Bi_4.5Ti₄O₁₅ (NBT) high temperature piezoelectric ceramics. In this paper, the crystal structure, electrical properties, and thermal stability of the B-site Mn/Nb co-doped Na_0.5Bi_4.5Ti_4-x(Mn_1/3Nb_2/3)_xO₁₅ (NBT-100x) ceramics were systematically investigated by the conventional solid-state reaction method. The crystal structural analysis results indicate that the NBT-100x ceramics have typical bismuth oxide layer type phase structure and high anisotropic plate-like morphology. The lattice parameters and the grain sizes increase with the B-site Mn/Nb co-doped content. The electrical properties were significantly improved by Mn/Nb co-doped modifications. The maximum of the piezoelectric coefficient d₃₃ was found to be 29 pC/N for the NBT-2 ceramics, nearly twice that of the unmodified NBT ceramics. The highest values of the planar electromechanical coupling factor k_p and thickness electromechanical coupling factor k_t were also obtained for the NBT-2 ceramics, at 5.4% and 31.2%, respectively. The dielectric spectroscopy showed that the Curie temperature Tc of the Mn/Nb co-doped NBT-100x ceramics is slightly higher than that of unmodified NBT ceramics (646 °C). The DC resistivity of the NBT-2 ceramics is higher than 10⁶ Ω∙cm at 500 °C. All the results together with the good thermal stability demonstrated the Mn/Nb co-doped ceramics as an effective method to improve the NBT based piezoelectric ceramics and the potential candidates of the Mn/Nb co-doped NBT-100x ceramics for high temperature piezoelectric applications. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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13 pages, 3838 KiB

Open AccessArticle

First-Principle Study on Correlate Structural, Electronic and Optical Properties of Ce-Doped BaTiO₃

by Haojie Yue, Kailing Fang, Tiantian Chen, Qinfang Jing, Kun Guo, Zhiyong Liu, Bing Xie, Pu Mao, Jinshan Lu, Francis Eng Hock Tay, Ivan Tan and Kui Yao

Crystals 2023, 13(2), 255; https://doi.org/10.3390/cryst13020255 - 1 Feb 2023

Cited by 7 | Viewed by 2328

Abstract

The structural, electronic, and optical properties of pure and Ce-doped BaTiO₃ were investigated based on first-principle calculation. Here, we concentrate on understanding the effect of the substitution of Ce for Ba and Ti sites in the equilibrium lattice parameters, DOS, electronic band structure, and optical performance of the materials. The crystal structures with a 12.5% doping ratio at different sites were constructed by superseding an atom of Ba (or Ti) site with a Ce atom and investigating the optimized crystal structure parameters. The substitution of Ce leads to a reduction in the band gap by inducing the movement of the conduction band minimum (CBM) and valence band maximum (VBM). The reduction in the band gap has been shown to be beneficial in increasing electrical conductivity. The density of states of the materials was calculated to gain insight into the valence band, conduction band, and contribution of each orbital to the total density of states in the electronic structure. The charge density, Mulliken charges, and bond overlap populations of pristine and Ce-doped BaTiO₃ were calculated to understand the nature of chemical bonds before and after doping. In addition, the optical properties of the materials were calculated, and the substitution of Ce for Ba site increased the static dielectric constant. In contrast, it decreased when Ce was doped into the Ti site. The substitution of Ce for different sites reduced the reflectivity of the material, while the transparency of the materials before and after doping was almost the same. The materials were transparent to incident light when the photon energy was below 10 eV, whereas opacity was in the ultraviolet range of 10–13 eV and beyond 20 eV. The theoretical calculation of different properties provides a new idea for the theoretical study of the BaTiO₃-based system. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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8 pages, 2751 KiB

Open AccessArticle

Effect of Sintering Conditions on the Electrical Properties of Lead-Free Piezoelectric Potassium Sodium Niobate-Based Ceramics

by Yan Tang, Lingyan Wang, Wei Ren, Yi Quan, Jinyan Zhao, Zhe Wang, Kun Zheng, Jian Zhuang and Gang Niu

Crystals 2022, 12(12), 1784; https://doi.org/10.3390/cryst12121784 - 8 Dec 2022

Cited by 1 | Viewed by 1463

Abstract

Lead-free piezoelectric 0.92(K_0.445Na_0.5Li_0.05)NbO₃-0.08BaZrO₃ (KNLN-BZ) ceramics were prepared via conventional sintering. Single-step, 2-step and 3-step temperature-controlled conditions were designed. The structure and electrical properties of ceramics obtained using different temperature-controlled procedures were systematically studied. It was found that ceramic prepared using the 3-step method with a holding time of 20 h showed the highest electrical properties. The Curie temperature was approximately 286 °C, and the dielectric constant and dielectric loss at room temperature were 1350 and 4.5% at the frequency of 1 kHz, respectively. The highest remanent polarization, piezoelectric strain and piezoelectric coefficient, d₃₃*, were obtained 60 °C, indicating a phase transition between ferroelectric phases. Although the ceramics did not show excellent piezoelectric properties, the 3-step sintering method can be considered an effective method to optimize the electrical performances of KNN-based ceramics. Combined with an appropriate composition, ceramics with excellent electrical properties could be obtained. This study provides a path to enhance the density and electrical properties for KNN-based ceramics with simple composition and potential for industry application. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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12 pages, 4395 KiB

Open AccessArticle

The Effect of Nb₂O₅ Precursor on KNN-Based Ceramics’ Piezoelectricity and Strain Temperature Stability

by Ruilin Han, Tingting Gao, Yining Xie, Lixu Xie, Yuan Cheng, Xu Li, Hao Chen, Jie Xing and Jianguo Zhu

Crystals 2022, 12(12), 1778; https://doi.org/10.3390/cryst12121778 - 7 Dec 2022

Cited by 3 | Viewed by 1927

Abstract

The performance of potassium sodium niobate ((K, Na) NbO₃, KNN)-based lead-free piezoelectric ceramics has significantly improved over the past decade. However, the performance bottlenecks of KNN-based ceramics cannot be ignored. Here, the Nb₂O₅ precursor is obtained after thermal pretreatment, which can evidently improve the piezoelectric properties and strain temperature stability of KNN-based ceramics. With the help of the Nb₂O₅ precursor treated at 800 °C, the optimal piezoelectric constant d₃₃ of 303 pC/N, inverse piezoelectric constant

{\overset{*}{d}}_{33}

of 378 pm/V, Curie temperature T_C of 310 °C and electromechanical coupling factor k_p of 42% are obtained, and the value of d₃₃ improves by about 30% compared with that of the ceramic prepared with untreated Nb₂O₅ as raw material. Additionally, in comparison with the strain temperature stability of the ceramics prepared with untreated Nb₂O₅ as raw material, the temperature stability is enhanced. Therefore, this study provides a useful approach to break the existing performance bottleneck and further improve the properties of KNN-based ceramics. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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11 pages, 4561 KiB

Open AccessArticle

Facile Preparation, Microstructure and Dielectric Properties of La(Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃ Perovskite High-Entropy Ceramics

by Zhifeng Tian, Ying Zhang, Junzhan Zhang and Peng Shi

Crystals 2022, 12(12), 1756; https://doi.org/10.3390/cryst12121756 - 4 Dec 2022

Cited by 2 | Viewed by 1914

Abstract

Preparation and properties of La(Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃ high-entropy ceramics are investigated. La(Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃ high-entropy ceramics are prepared by a traditional two-step solid-state reaction method in air. La(Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃ single-phase powders are synthesized by calcining the mixed oxides at 1000 °C for 20 h. The high-entropy ceramics are sintered at 1350–1650 °C in a muffle furnace for 4 h by using the above powders. The phase compositions of the high-entropy ceramics at different temperatures are characterized by X-ray diffraction (XRD) with Cu Kα radiation. A field-emission scanning electron microscope with energy-dispersive spectroscopy (EDS) is used to observe the microstructures and analyze the elemental distributions. The hardness and dielectric properties are measured and discussed. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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16 pages, 4551 KiB

Open AccessArticle

Study of Co-Doped K₂Ti₆O₁₃ Lead-Free Ceramic for Positive Temperature Coefficient Thermistor Applications

by Mohammad Shariq, Mohd Asim Siddiqui, Muhammad Azam Qamar, Y. Altowairqi, Syed Kashif Ali, Osama Madkhali, Mohammed M. Fadhali, T. Alharbi, Mohd. Shakir Khan, Imam Saheb Syed, Zeyad M. Ahmed and Majed Yousef Awaji

Crystals 2022, 12(11), 1569; https://doi.org/10.3390/cryst12111569 - 3 Nov 2022

Cited by 5 | Viewed by 1638

Abstract

Cobalt-doped potassium hexa-titanate (Co_x:K₂Ti₆O₁₃ (x = 0.05, 0.10, 0.15 mole%)) ceramics were synthesized by the solid-state reaction method. The XRD patterns confirmed single-phase development in a monoclinic symmetry of various samples, and they were used for different structural calculations of Co_x:K₂Ti₆O₁₃ ceramics. The dielectric constant, tanδ, electrical modulus, and ac conductivity of Co-doped K₂Ti₆O₁₃ were studied in the temperature range of 100–500 °C. Anomalies were observed in graphs of the dielectric constant versus temperature, showing the transition phase in the studied samples. Dielectric peaks at transition temperature decreased with an increasing frequency, and the peaks shifted toward higher temperatures, illustrating the relaxation of the dielectric materials. The composition with x = 0.10 showed low dielectric loss and a higher dielectric constant and can be utilized for high-temperature dielectric material. Small doping of cobalt improved the ac conductivity of K₂Ti₆O₁₃ ceramics due to the increase in the spin–phonon interaction and dominant electron hopping conduction; however, the conductivity diminished with substantial doping because of the contraction of the tunnel space and ambushing of conduction electrons. The uniqueness of this study is in the high dielectric optimization of lead-free ceramic Co_x:K₂Ti₆O₁₃ and the discovery of positive temperature coefficients of the resistivity of these ceramic samples. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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13 pages, 3750 KiB

Open AccessArticle

Effects of Sb Doping on Electrical Conductivity Properties in Fine-Grain KNN-Based Ferroelectric Ceramics

by Jiahao Jiang, Shuaimin Chen, Chunlin Zhao, Xiao Wu, Min Gao, Tengfei Lin, Changqing Fang and Cong Lin

Crystals 2022, 12(9), 1311; https://doi.org/10.3390/cryst12091311 - 17 Sep 2022

Cited by 7 | Viewed by 2127

Abstract

In this work, the effects of Sb doping on the electrical conductivity of fine-grain 0.9(K_0.5Na_0.5)(Nb_1−xSb_x)O₃-0.1Bi(Ni_2/3Nb_1/3)O₃ (KNNSx-BNN) ceramics were systemically investigated. It was found that the grain size decreases from ~900 nm (x = 0) to ~340–400 nm (x = 0.06–0.08), and then increases again to ~700 nm (x = 0.10). This is because the solubility limit of Sb doping is about 0.08 in this ceramic, and more Sb doping will facilitate the grain growth as the sintering aids. Impedance and conductivity analyses reveal that the grain resistance and its activation energy show a similar changing tendency with grain size, while grain boundary conductivity steadily increases after Sb doping. In this process, the grain contribution on ceramic conductivity changes with grain size variation, and grain boundary contribution becomes more obvious with increasing doping content. The reduction in grain size, improvement in grain boundary density and doping ions entering into the grain boundary should contribute to the evolution of electrical conductivity properties after Sb doping in KNN-based ferroelectric ceramics. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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11 pages, 4770 KiB

Open AccessArticle

Fabrication and Characterization of Lead-Free BNT-6BT Ultrasonic Transducers Designed by an Intelligent Optimization Algorithm

by Junshan Zhang, Jianxin Zhao, Yi Quan, Jingrong He, Yi Li, Zhe Wang, Kun Zheng, Jian Zhuang, Zhishui Jiang, Li Wen and Wei Ren

Crystals 2022, 12(8), 1181; https://doi.org/10.3390/cryst12081181 - 22 Aug 2022

Cited by 2 | Viewed by 2214

Abstract

Lead-free piezoelectric material-based ultrasonic transducers have been researched for several years, but the inefficient properties and design difficulties have troubled lead-free ultrasonic transducers for a long time. To improve the performance and design efficiency of lead-free ultrasonic transducers, in this work, an equivalent circuit model and intelligent optimization algorithm were combined for use in a transducer design. Firstly, 0.94(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃(BNT-6BT) lead-free piezoelectric ceramics were prepared and characterized. Then, BNT-6BT ceramics were used to fabricate the ultrasonic transducers. An equivalent circuit model-based software, PiezoCAD, and a genetic algorithm-based back-propagation neural network were used to optimize the design of the transducers. A 3.03 MHz center frequency and 60.3% −6 dB bandwidth of the optimized transducers were achieved, which were consistent with the neural networks optimization results. To verify the application potential of the lead-free transducers, tungsten rods phantom imaging and polystyrene spheres with 300 μm diameter manipulation were completed by the transducers, and the experiment results indicate that the BNT-6BT lead-free transducers have great potential in further biological and biomedical applications. Full article

(This article belongs to the Special Issue Lead-free Ferro-/Piezoelectric Ceramics and Thin Films)

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