Crystals

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11 pages, 3769 KiB

Open AccessArticle

Enhancement of Thermoelectric Performance for InTe by Selective Substitution and Grain Size Modulation

by Menghui Zhou, Juan Li, Guoying Dong, Shufang Gao, Jianghe Feng and Ruiheng Liu

Crystals 2023, 13(4), 601; https://doi.org/10.3390/cryst13040601 - 1 Apr 2023

Cited by 4 | Viewed by 1544

The different masses, ionic radii, and chemical valences of the nonequivalent crystallographic sites of thermoelectric (TE) compounds provide an effective way to modulate the thermoelectric performance by selective substitution. In this work, the selective substitution of In⁺ by Pb for the binary [...] Read more.

The different masses, ionic radii, and chemical valences of the nonequivalent crystallographic sites of thermoelectric (TE) compounds provide an effective way to modulate the thermoelectric performance by selective substitution. In this work, the selective substitution of In⁺ by Pb for the binary InTe material monotonically reduces the carrier concentration, which is greatly beneficial to the mechanism investigation of serious grain boundary scattering (GBS). This is the first time this point has been mentioned with regard to InTe material. As a result, we found that GBS was dominated by the grain size when the carrier concentration was higher than 0.7 × 10¹⁹ cm⁻³ but was inversely governed by the carrier concentration when the carrier was situated at a lower density. In particular, the occupation of Pb on the targeted In⁺ site could further reduce the lattice thermal conductivity. Finally, In_0.9999Pb_0.0001Te achieved the improved power factor and average zT value, which could contribute to high-power generation below a medium temperature. This effect of increasing the carrier concentration on the suppression of GBS sheds light on the possibility of improving electron mobility by increasing the carrier concentration. Full article

(This article belongs to the Special Issue Advanced Electronic Materials and Devices)

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18 pages, 14308 KiB

Open AccessArticle

Effect of Bi³⁺ Doping on the Electronic Structure and Thermoelectric Properties of (Sr_0.889-xLa_0.111Bi_x)TiO_2.963: First-Principles Calculations

by Lingyun Gong, Ping Zhang, Zhihao Lou, Ziyao Wei, Zhuozhao Wu, Jie Xu, Xuanjie Chen, Weihang Xu, Yiqi Wang and Feng Gao

Crystals 2023, 13(2), 178; https://doi.org/10.3390/cryst13020178 - 19 Jan 2023

Cited by 2 | Viewed by 1582

Abstract

The electronic structure and thermoelectric properties of Bi³⁺-doped (Sr_0.889-xLa_0.111Bi_x)TiO_2.963 were studied by the first principles method. Doping Bi³⁺ can increase the cell parameters, cell asymmetry and band gap. With increasing Bi³⁺ content, [...] Read more.

The electronic structure and thermoelectric properties of Bi³⁺-doped (Sr_0.889-xLa_0.111Bi_x)TiO_2.963 were studied by the first principles method. Doping Bi³⁺ can increase the cell parameters, cell asymmetry and band gap. With increasing Bi³⁺ content, the asymmetry of DOS relative to the Fermi level increases, which results in an enhanced Seebeck coefficient, increasing carrier mobility and decreasing carrier concentration. An appropriate Bi³⁺-doping concentration (7.4–14.8%) can increase the lattice distortion and reduce the lattice thermal conductivity of the material. An appropriate Bi³⁺-doping concentration (7.4%) can effectively optimize the electrical transport performance and improve the thermoelectric properties of strontium titanate. The optimal Bi³⁺-doping concentration is 7.4%, and Sr_0.815La_0.111Bi_0.074TiO_2.963 obtains a maximum ZT of 0.48. This work shows the mechanism of Bi³⁺ doping in enhancing the thermoelectric properties of strontium titanate. Full article

(This article belongs to the Special Issue Advanced Electronic Materials and Devices)

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8 pages, 2106 KiB

Open AccessArticle

Positive and Negative Electrocaloric Effect in Lead-Free Silver Niobate Antiferroelectric Ceramic Depending on Affluent Phase Transition

by Jinhua Du, Ye Zhao, Yong Li, Ningning Sun and Xihong Hao

Crystals 2023, 13(1), 86; https://doi.org/10.3390/cryst13010086 - 2 Jan 2023

Cited by 1 | Viewed by 1574

Abstract

We prepared a dense AgNbO₃ ceramic using a conventional solid-state reaction method. The phase structure, electrical properties and electrocaloric effect (ECE) were systematically investigated. Large negative and positive ECEs (−4.38 °C at 65 °C and 2.3 °C at 210 °C) under an [...] Read more.

We prepared a dense AgNbO₃ ceramic using a conventional solid-state reaction method. The phase structure, electrical properties and electrocaloric effect (ECE) were systematically investigated. Large negative and positive ECEs (−4.38 °C at 65 °C and 2.3 °C at 210 °C) under an external electric field of 180 kV·cm⁻¹ were obtained in the eco-friendly AgNbO₃ antiferroelectric (AFE) ceramic due to affluent phase transition and a high electric field. The large positive and negative ECEs originated from the phase transition between ferrielectric (FIE) phases (the orthorhombic space group (Pmc2₁) and AFE phases (Pbcm) tuned by an applied external field. Additionally, a probable mechanistic model was proposed to illustrate the generation of positive and negative ECEs. This study may provide guidelines for the design of high-efficiency solid-state cooling devices. Full article

(This article belongs to the Special Issue Advanced Electronic Materials and Devices)

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15 pages, 4688 KiB

Open AccessArticle

Electrical and Dielectric Properties of Ca-Doped Bi-Deficient Sodium Bismuth Titanate Na_0.5Bi_0.49−xCa_xTiO_3−δ (0 ≤ x ≤ 0.08)

by Fan Yang, Yidong Hu, Qiaodan Hu, Patrick Wu and Derek C. Sinclair

Crystals 2022, 12(12), 1800; https://doi.org/10.3390/cryst12121800 - 10 Dec 2022

Cited by 4 | Viewed by 2204

Abstract

Bismuth-deficient sodium bismuth titanate (nominal Na_0.5Bi_0.49TiO_2.985, NB_0.49T) presents high oxide ion conductivity, which makes it a potential electrolyte material for intermediate-temperature solid oxide fuel cells. Acceptor doping has been proven an effective approach to enhance [...] Read more.

Bismuth-deficient sodium bismuth titanate (nominal Na_0.5Bi_0.49TiO_2.985, NB_0.49T) presents high oxide ion conductivity, which makes it a potential electrolyte material for intermediate-temperature solid oxide fuel cells. Acceptor doping has been proven an effective approach to enhance the bulk conductivity (σ_b) of NB_0.49T. Here, divalent Ca²⁺ ions were selected to partially replace Bi³⁺ on the A-site of NB_0.49T, and the temperature and composition dependences of σ_b and permittivity were investigated. Results showed that Ca²⁺ doping was effective for enhancing σ_b of NB_0.49T by creating oxygen vacancies. The highest σ_b (0.006 S·cm⁻¹ at 500 °C) was achieved by 2% Ca²⁺ doping. Further increase in the doping level decreased σ_b, which was more pronounced at temperatures below ~350 °C. Most importantly, Ca doping increased the temperature at which the activation energy for bulk conduction changed from ~0.80 eV (at low temperatures) to ~0.40 eV (at high temperatures), and reduced the temperature dependence of permittivity of NB_0.49T. Results from the average structural parameters and the local defect associates are discussed. The findings of this work are helpful for understanding the defect and conduction mechanisms for acceptor-doped NB_0.49T, and are also useful for developing NBT-based dielectrics with temperature-independent permittivity. Full article

(This article belongs to the Special Issue Advanced Electronic Materials and Devices)

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10 pages, 3688 KiB

Open AccessArticle

Rare Earth Ion-Doped Y_2.95R_0.05MgAl₃SiO₁₂ (R = Yb, Y, Dy, Eu, Sm) Garnet-Type Microwave Ceramics for 5G Application

by Zijun Ye, Yu Jiang, Minmin Mao, Zhiyu Xiu, Mengjiao Chi, Guofa Wu, Bing Liu, Dawei Wang, Bin Yang and Kaixin Song

Crystals 2022, 12(11), 1608; https://doi.org/10.3390/cryst12111608 - 11 Nov 2022

Cited by 6 | Viewed by 1674

Abstract

In this work, Y_2.95R_0.05MgAl₃SiO₁₂ (R = Yb, Y, Dy, Eu, Sm) microwave single-phase dielectric ceramics were successfully prepared via a conventional ceramic sintering technology by doping a series of rare earth elements (Yb, Y, Dy, Eu, [...] Read more.

In this work, Y_2.95R_0.05MgAl₃SiO₁₂ (R = Yb, Y, Dy, Eu, Sm) microwave single-phase dielectric ceramics were successfully prepared via a conventional ceramic sintering technology by doping a series of rare earth elements (Yb, Y, Dy, Eu, Sm) with different ionic radii for the first time. The effects of A-sites occupied by rare earth elements on the microwave dielectric properties of Y_2.95R_0.05MgAl₃SiO₁₂ were studied using crystal structure refinement, a scanning electron microscope (SEM), bond valence theory, P-V-L theory, and infrared reflection spectroscopy. It was found that the ionicity of the Y-O bond, the lattice energy, the bond energy, and the bond valance of the Al_(Tet)-O bond had important effects on the microwave dielectric properties. Particularly, the optimum microwave dielectric properties, ε_r = 9.68, Q × f = 68,866 GHz, and τ_f = −35.8 ppm/°C, were obtained for Y_2.95Dy_0.05MgAl₃SiO₁₂ when sintered at 1575 °C for 6 h, displaying its potential for 5G communication. Full article

(This article belongs to the Special Issue Advanced Electronic Materials and Devices)

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11 pages, 1109 KiB

Open AccessFeature PaperArticle

Electron and Hole Mobility of SnO₂ from Full-Band Electron–Phonon and Ionized Impurity Scattering Computations

by Zhen Li, Patrizio Graziosi and Neophytos Neophytou

Crystals 2022, 12(11), 1591; https://doi.org/10.3390/cryst12111591 - 9 Nov 2022

Cited by 9 | Viewed by 2933

Abstract

Mobility is a key parameter for SnO₂, which is extensively studied as a practical transparent oxide n-type semiconductor. In experiments, the mobility of electrons in bulk SnO₂ single crystals varies from 70 to 260 cm²V⁻¹s [...] Read more.

Mobility is a key parameter for SnO₂, which is extensively studied as a practical transparent oxide n-type semiconductor. In experiments, the mobility of electrons in bulk SnO₂ single crystals varies from 70 to 260 cm²V⁻¹s⁻¹ at room temperature. Here, we calculate the mobility as limited by electron–phonon and ionized impurity scattering by coupling the Boltzmann transport equation with density functional theory electronic structures. The linearized Boltzmann transport equation is solved numerically beyond the commonly employed constant relaxation-time approximation by taking into account all energy and momentum dependencies of the scattering rates. Acoustic deformation potential and polar optical phonons are considered for electron–phonon scattering, where polar optical phonon scattering is found to be the main factor which determines the mobility of both electrons and holes at room temperature. The calculated phonon-limited electron mobility is found to be 265 cm²V⁻¹s⁻¹, whereas that of holes is found to be 7.6 cm²V⁻¹s⁻¹. We present the mobility as a function of the carrier concentration, which shows the upper mobility limit. The large difference between the mobilities of n-type and p-type SnO₂ is a result of the different effective masses between electrons and holes. Full article

(This article belongs to the Special Issue Advanced Electronic Materials and Devices)

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7 pages, 2291 KiB

Open AccessArticle

Bi_0.5Na_0.5TiO₃-Bi_3.25La_0.75Ti₃O₁₂ Lead-Free Thin Films for Energy Storage Applications through Nanodomain Design

by Wenfeng Yue, Tingting Jia, Yanrong Chen, Wenbin Dai, Liang Yu, Yali Cai, Ting Li, Lixia Liu, Quansheng Guo and Shuhui Yu

Crystals 2022, 12(11), 1524; https://doi.org/10.3390/cryst12111524 - 26 Oct 2022

Cited by 6 | Viewed by 1653

Abstract

Dielectric capacitors have received increasing attention due to their high power density. The Bi-based Aurivillius phase compound Bi_3.25La_0.75Ti₃O₁₂ (BLT) is considered a potential material in the field of energy storage due to its excellent ferroelectric properties [...] Read more.

Dielectric capacitors have received increasing attention due to their high power density. The Bi-based Aurivillius phase compound Bi_3.25La_0.75Ti₃O₁₂ (BLT) is considered a potential material in the field of energy storage due to its excellent ferroelectric properties and good fatigue resistance, and temperature stability. In this paper, 0.4Bi_0.5Na_0.5TiO₃-0.6Bi_3.25La_0.75Ti₃O₁₂ (0.4NBT4BNT-0.6BLT)-thin films were prepared on Pt/Ti/SiO₂/Si substrates with the sol-gel method. The addition of BNT destroys the long-range ferroelectric order of BLT and forms nanodomains. By increasing the BNT content, the BLT is transformed from a ferroelectric state to a relaxed state, and its application in the field of energy storage is realized. The recoverable energy density is 42.41 J/cm³, and the recoverable energy storage density is relatively stable in the range of 25–200 °C with good thermal stability. The energy storage efficiency is 75.32% at ~2663 kV/cm. The leakage current density at 300 kV/cm is 1.06 × 10⁻⁹ A/cm². Full article

(This article belongs to the Special Issue Advanced Electronic Materials and Devices)

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11 pages, 3437 KiB

Open AccessArticle

High Thermal Stability and Color Purity of Y₂SrAl₄SiO₁₂: Eu³⁺ Garnet-Variant-Structured Phosphor for Warm White Light LED-Lamp

by Xinhua Chen, Qingliang Xu, Fayaz Hussain, Chen Yang, Weiqin Sheng, Xinjiang Luo, Bing Liu, Shikuan Sun, Dawei Wang and Kaixin Song

Crystals 2022, 12(10), 1382; https://doi.org/10.3390/cryst12101382 - 29 Sep 2022

Cited by 6 | Viewed by 2182

Abstract

Red LEDs with a high color purity and high color rendering index are often used to compensate for the lack of red-light components in current white LEDs. Therefore, the new type of garnet-structured high color purity red phosphor Y_2−xSrAl₄SiO [...] Read more.

Red LEDs with a high color purity and high color rendering index are often used to compensate for the lack of red-light components in current white LEDs. Therefore, the new type of garnet-structured high color purity red phosphor Y_2−xSrAl₄SiO₁₂: xEu³⁺ was synthesized by the solid-state method. The band gap structure of the host matrix was studied through the DFT calculation and found that the matrix belongs to a direct band gap structure with a band gap size of 4.535 ev. The phosphor exhibits a wide excitation spectrum under the monitoring of 710 nm. The strongest excitation wavelength is 393 nm, and it exhibits bright red light under the excitation of 393 nm, and the emission peak positions are located at 570 nm, 597 nm, 613 nm, 650 nm, 710 nm and 748 nm, respectively, which are attributed to the ⁵D₀→⁷F_j of Eu³⁺ (j = 0–5) electronic transitions. In the crystal structure of Y₂SrAl₄SiO₁₂, Eu³⁺ occupies a symmetry site. The compositional changes and thermal studies found favorable at 20% mol. At this concentration, the luminescence intensity gradually weakened due to the Eu³⁺ electric multi-level interaction. It is worth noting that the emission intensity of Y₂SrAl₄SiO₁₂: 20%Eu³⁺ at 433 K can be maintained to 92% of that at 293 K. Finally, we combined it with the NUV chip and packaged it into a red LED with a color purity of up to 90% and a correlated color temperature of 1492 K. The high purity, low color temperature and thermal stability indicate that it has a place in LED applications. Full article

(This article belongs to the Special Issue Advanced Electronic Materials and Devices)

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