Article
Nanoscience & Nanotechnology
Xiaodong Liu, Demie Kepaptsoglou, Zhaohe Gao, Andrew Thomas, Krishnendu Maji, Emmanuel Guilmeau, Feridoon Azough, Quentin M. Ramasse, Robert Freer
Summary: This study focuses on the preparation of donor-doped TiO2 ceramics and their effects on thermoelectric properties at a microscopic level; optimizing carrier concentration and electrical conductivity by controlling defect structures to achieve an enhanced power factor; meanwhile, successfully reducing lattice thermal conductivity for improved thermoelectric conversion efficiency.
ACS APPLIED MATERIALS & INTERFACES
(2021)
Article
Materials Science, Ceramics
Nhat Quang Minh Tran, Anh Tuan Thanh Pham, Cuong Chi Nguyen, Tien Thuy Nguyen Tran, Hoa Thi Lai, Thu Bao Nguyen Le, Chalicheemalapalli Kulala Jayasankar, Wisanu Pecharapa, Thang Bach Phan
Summary: This study introduces a novel strategy for improving the thermoelectric performance of oxide-based materials by synthesizing nanostructured phonon-glass multi-phase ceramic material. The addition of a secondary pentacolumn phase further reduces the lattice thermal conductivity and enhances the ZT value to twice the intrinsic value of the base materials.
CERAMICS INTERNATIONAL
(2023)
Article
Materials Science, Ceramics
Yixuan Shi, Zahra Sepahi, Leilane R. Macario, Cheryl Sturm, Nour Mashmoushi, Yaron Amouyal, Holger Kleinke
Summary: We studied the impact of varying amounts of CaO layers on the thermoelectric properties of the Ruddlesden-Popper series CaO(CaMnO3)(m) with m = 1, 2, 3, infinity. Dense pellets were obtained through extended ball-milling and hot-pressing, with the sample containing the most CaO layers (m = 1) exhibiting the lowest electrical and thermal conductivity and the highest Seebeck coefficient. Ultimately, the perovskite CaMnO3 (m = infinity) without CaO layers showed the best thermoelectric properties.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2023)
Review
Chemistry, Physical
Xiaoping Wu, Haibo Wang, Yu Wang
Summary: Magneli phase titanium oxides, also known as titanium sub-oxides, are electrically conducting ceramic materials with attractive properties such as electrical conductivity, corrosion resistance and optical properties. The synthesis of nanostructured titanium sub-oxides has been making progress and they have potential applications in conducting materials, fuel cells, coatings, and electronic and optoelectronic devices.
Review
Materials Science, Multidisciplinary
Albert A. Voskanyan, Alexandra Navrotsky
Summary: This review summarizes the recent research on crystallographic shear structures, including the geometrical and mechanistic aspects of shear plane formation and propagation. It also discusses the energetics and thermodynamic stability of shear compounds, along with highlighting the remaining challenges and proposing future directions in this area.
ANNUAL REVIEW OF MATERIALS RESEARCH, VOL 51, 2021
(2021)
Article
Nanoscience & Nanotechnology
Xiaodong Liu, Demie Kepaptsoglou, Ewa Jakubczyk, Jincheng Yu, Andrew Thomas, Bing Wang, Feridoon Azough, Zhaohe Gao, Xiangli Zhong, Robert Dorey, Quentin M. Ramasse, Robert Freer
Summary: High-performance Nb-doped TiO2 thick films with enhanced thermoelectric performance are fabricated using facile and scalable screen-printing techniques. The films exhibit different defect structures, including crystallographic shear (CS) structures, twin boundaries, and Al-segregated CS structures, which contain abundant oxygen vacancies and enable energy-filtering effects. These CS structures contribute to the simultaneous enhancement of electrical conductivity and Seebeck coefficients, resulting in the highest power factor observed in TiO2-based TE films at elevated temperatures. The microstructure modification strategy provides a novel route for atomic-level defect engineering.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Nanoscience & Nanotechnology
Bojana Visic, Luka Pirker, Marko Opacic, Ana Milosavljevic, Nenad Lazarevic, Boris Majaron, Maja Remskar
Summary: Four distinct tungsten suboxide nanomaterials were synthesized and their crystal structures were found to play a significant role in their optical properties. The different crystal structures affect the bandgap, localized surface plasmon resonances, and excitonic transitions.
Article
Physics, Applied
Tingting Yuan, Na Jin, Wenyu Cheng, Yuyang Yun, Xin Tian, Lu Wang, Jinwen Ye
Summary: In this study, the impact of doping on the thermodynamic and structural stability of Ti4O7 was investigated using density functional theory and machine learning. The results showed that certain rare earth elements and transition metals can improve the stability of Ti4O7, and machine learning can be used to predict the stability of doped materials, providing a new approach for defect engineering.
APPLIED PHYSICS LETTERS
(2022)
Article
Chemistry, Multidisciplinary
Hiren S. Patel, Vishnu A. Dabhi, Aditya M. Vora
Summary: This study investigates the electronic, optical, thermodynamic, and thermoelectric properties of strontium oxide (SrO) and strontium peroxide (SrO2) using density functional theory. The materials show promising optoelectronic properties and potential applications in ultraviolet sensors. The maximum figure of merit for the thermoelectric properties reaches 0.5.
Article
Materials Science, Multidisciplinary
Jung Sang You, Man Jin Eom, Minhyea Lee, Y. J. Jo, C. J. Won, S-W Cheong, Kyoo Kim, Jun Sung Kim
Summary: The study revealed that stripe-charge ordering in IrTe2 leads to Fermi surface reconstruction, resulting in abrupt changes in thermoelectric power and Hall effect, which are attributed to multiband conduction.
Article
Chemistry, Inorganic & Nuclear
Roger I. Bickley, Gerald R. Garside, Teresita Gonzalez-Carreno, Agustin R. Gonzalez-Elipe, J. Antonio Navio
Summary: A model is proposed to determine the size of acicular octadecahedral microcrystallites of rutile titanium dioxide powder. Reduction, ESR, electrical conductivity and controlled re-oxidation techniques were used to study reduced microcrystallites. The model suggests the presence of paramagnetic and spin-paired sites on the external crystal faces and polygonal bulk crystallographic shear structures. These shear structures are oxidized at different rates on the microcrystallite faces by anionic vacancy transfer.
JOURNAL OF SOLID STATE CHEMISTRY
(2023)
Article
Engineering, Electrical & Electronic
Pan Ren, Trevor P. Bailey, Alexander A. Page, Quanxin Yang, Tu Lv, Guiying Xu
Summary: This study reports the preparation and thermoelectric properties of iodine-doped n-type nano-polycrystalline MoTe2, which showed significantly enhanced carrier concentration and power factor, and reduced thermal conductivity. The research also revealed that dislocation scattering is the main mechanism, with thermal conductivity rapidly decreasing with increasing temperature and doping.
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS
(2021)
Article
Chemistry, Inorganic & Nuclear
Yuheng Gao, Xin Niu, Lin Pan, Yudong Lang, Changchun Chen, Yifeng Wang
Summary: The effects of MoS2 addition on the thermoelectric properties of Bi2O2Se were investigated in this study. The results show that the introduction of MoS2 can improve the efficiency of the liquid assisted shear exfoliation process, increase the porosity and inhibit the grain growth of Bi2O2Se. Accordingly, the electrical conductivity decreases first and then increases with the increase of the MoS2 content. Besides, the absolute Seebeck coefficient |S| of the composite sample rises first and then decreases with the increase of the MoS2 content due to the offset effect between |S| and sigma. In addition, the enhanced phonon scattering combined with the increased porosity by MoS2 addition significantly inhibited the lattice thermal conductivity of Bi2O2Se. Finally, a ZTmax of 0.55 for 0.3 mol%MoS2/Bi2O2Se at 773 K was obtained.
SOLID STATE SCIENCES
(2023)
Article
Engineering, Electrical & Electronic
Salman Ali Khan, Hidayat Ullah Khan, Shahid Mehmood, Zahid Ali
Summary: The study of structural phases of silver tantalate using density functional theory confirmed the stability of the monoclinic phase compared to the rhombohedral phase, with potential applications in optoelectronic devices. The compound showed promising optical properties and thermoelectric properties, making it a potential candidate for thermoelectric devices.
MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING
(2021)
Article
Crystallography
Yuui Yokota, Shigeru Horii, Hiraku Ogino, Yoshiyuki Yoshida, Akira Yoshikawa
Summary: By controlling the growth rate, the morphology and thermoelectric properties of La:STO/TO eutectic crystals can be adjusted, with faster growth rates leading to higher figures of merit ZT.
JOURNAL OF CRYSTAL GROWTH
(2022)
Article
Physics, Applied
Akira Kawata, Kenta Murayama, Shogo Sumitani, Shunta Harada
Summary: An automatic detection algorithm was designed to detect the positions of dislocation contrasts in semiconductor crystals, utilizing the characteristic feature of black and white contrasts of the dislocations and a variance filter to identify large changes in contrast levels. The algorithm successfully achieves a relatively high precision and sensitivity in detecting the dislocation contrasts.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2021)
Article
Physics, Applied
Nobuhiko Kokubo, Yosuke Tsunooka, Sho Inotsume, Fumihiro Fujie, Shoichi Onda, Hisashi Yamada, Mitsuaki Shimizu, Shunta Harada, Miho Tagawa, Toru Ujihara
Summary: Raman spectroscopy was used to demonstrate the strain field of tilted threading dislocations in a c-plane GaN single crystal grown by hydride vapor-phase epitaxy. The high-contrast areas and deformed contrast regions observed in the 2D mapping images provide insights into the Burgers vector edge component and tilted dislocations. Simulation results showed that a 60-degree tilted dislocation exhibited contrast extending in one direction, consistent with experimental line profiles of the E-2(H) peak shift.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2021)
Article
Nanoscience & Nanotechnology
Dengshan Zhou, Zhenghao Chen, Kazuki Ehara, Kodai Nitsu, Katsushi Tanaka, Haruyuki Inui
Summary: Research shows that the macroscopic mechanical strength of single crystals of equiatomic Cr-Mn-Fe-Co-Ni high entropy alloy, which are expected to develop short-range ordering during thermal annealing, is not affected. The hardness, critical resolved shear stress, and activation volume values of the alloy do not significantly vary with the annealing temperature.
SCRIPTA MATERIALIA
(2021)
Article
Materials Science, Multidisciplinary
Fumihiro Fujie, Hongyu Peng, Tuerxun Ailihumaer, Balaji Raghothamachar, Michael Dudley, Shunta Harada, Miho Tagawa, Toru Ujihara
Summary: The contrast features of synchrotron X-ray topographic images of screw-type basal plane dislocations in on-axis 4H-SiC wafers have been studied, and the correlation between the contrast features and the depth of the screw BPDs below the crystal surface has been demonstrated for estimating the depth.
Article
Chemistry, Physical
Shunta Harada, Naoki Kosaka, Miho Tagawa, Toru Ujihara
Summary: The ordered arrangement of planar faults in titanium oxide natural superlattices exhibits picoscale structural perfection, with an average periodicity disorder of 36 pm and interface roughness estimated to be 15 pm. Calculation of the specularity parameter indicates that the smooth interfaces in the titanium oxide NSL system can coherent control phonons with frequencies less than 23 THz.
JOURNAL OF PHYSICAL CHEMISTRY C
(2021)
Article
Chemistry, Multidisciplinary
Hayato Sumi, Noboru Ohta, Hiroshi Sekiguchi, Shunta Harada, Toru Ujihara, Katsuo Tsukamoto, Miho Tagawa
Summary: The study investigated the structural changes of DNA-functionalized nanoparticle superlattices after dehydration, finding that an optimal volume fraction of nanoparticles minimized distortion of the dehydrated superlattice for both bcc and fcc structures. The results suggest that crystal structures of solid nanoparticle superlattices can be designed via DNA-guided assembly followed by dehydration under nonequilibrium conditions.
CRYSTAL GROWTH & DESIGN
(2021)
Article
Chemistry, Physical
Mikio Oomae, Takeshi Teramoto, Katsushi Tanaka
Summary: The variations in positive temperature dependence of yield stress for L12 intermetallic compounds in pseudobinary alloys of Co3(Al, W)-Co3Ti were investigated. The activation energies are intermediate values between those of Co3(Al, W) and Co3Ti, and the composition dependence of the temperature dependence of yield stress can be predicted from the physical properties of the base compounds.
Article
Chemistry, Physical
Shunta Harada, Shunya Sugimoto, Naoki Kosaka, Miho Tagawa, Toru Ujihara
Summary: The atomic structure of titanium-chromium oxide natural superlattices with ordered crystallographic shear planes was investigated using STEM and electron diffraction. It was found that the atomic arrangements of CS planes changed depending on the chromium concentration. The CS planes in titanium-chromium oxides behaved as coherent interfaces for phonons.
JOURNAL OF PHYSICAL CHEMISTRY C
(2021)
Article
Materials Science, Multidisciplinary
Tuerxun Ailihumaer, Hongyu Peng, Fumihiro Fujie, Balaji Raghothamachar, Michael Dudley, Shunta Harada, Toru Ujihara
Summary: A more sophisticated simulation model based on ray-tracing principle has been developed to simulate synchrotron X-ray topographic contrast of dislocations in 4H-SiC crystals. Surface relaxation effects and photoelectric absorption effects play significant roles in determining dislocation contrast, with distinctive features observed in simulated dislocation images correlating well with experimental topographic images.
MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS
(2021)
Article
Materials Science, Multidisciplinary
Takeshi Teramoto, Momoko Narasaki, Katsushi Tanaka
Summary: In order to understand the complex mechanism of solid-solution strengthening in high-entropy alloys (HEAs), this study evaluates the effective atomic radii of constituent elements experimentally and finds a different order compared to previous theoretical calculations. While theoretical calculations suggest a correlation between yield stress and average atomic displacement in HEAs, this correlation is not confirmed by experimental results in this study.
PHILOSOPHICAL MAGAZINE LETTERS
(2022)
Article
Nanoscience & Nanotechnology
Shunta Harada, Naoki Kosaka, Takashi Yagi, Shunya Sugimoto, Miho Tagawa, Toru Ujihara
Summary: Research has shown that introducing crystallographic shear structures in titanium oxide superlattices can decrease thermal conductivity, although the decrease is not monotonic with increasing density of shear planes. Calculation of thermal conductivity and mean free path for phonons revealed a transition from incoherent to coherent thermal conduction, with coherent interfaces formed as thermodynamically stable phases in bulk titanium oxide superlattices with nanoscale periodicity.
SCRIPTA MATERIALIA
(2022)
Article
Materials Science, Multidisciplinary
Fumihiro Fujie, Shunta Harada, Hiromasa Suo, Balaji Raghothamachar, Michael Dudley, Kenji Hanada, Haruhiko Koizumi, Tomohisa Kato, Miho Tagawa, Toru Ujihara
Summary: The expansion of double Shockley stacking faults (DSFs) in an n-type 4H-SiC substrate with a nitrogen concentration of 3.9 x 10(19) cm(-3) was found to be suppressed and immobilized above 1590 K, with the shape of partial dislocation (PD) changing from straight to zig-zag configuration. Possible mechanism of this immobilization was proposed to involve non-conservative motion induced by the interaction between PDs and point defects.
Article
Chemistry, Physical
Takeshi Teramoto, Kentaro Kitasumi, Ryota Shimohara, Yusuke Ito, Ryouga Shimizu, Katsushi Tanaka, Rintaro Ueji
Summary: The variation in chemical short-range order (CSRO) in Cr-Co-Ni medium entropy alloy was studied using electrical resistivity measurements. The results showed that thermodynamic equilibrium above 1075 K could not be achieved in conventional sample preparations. The resistivity quenched at different temperatures increased with lower annealing temperature, especially below 873 K. The activation energy was determined to be 240-270 kJ mol-1 and was similar to atomic diffusion in the Cr-Mn-Fe-Co-Ni high-entropy alloy, indicating a link between resistivity change and atomic arrangement. Compression tests on single crystals with varying degrees of CSRO showed that the degree of CSRO did not significantly affect the early stages of plastic deformation.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Chemistry, Multidisciplinary
Wancheng Yu, Can Zhu, Yosuke Tsunooka, Wei Huang, Yifan Dang, Kentaro Kutsukake, Shunta Harada, Miho Tagawa, Toru Ujihara
Summary: In the design of a crystal growth system, efficiently regulating intertwined geometrical parameters is crucial. A machine learning approach developed in this study effectively accelerates the geometry optimization process, generating various possible solutions through a global search at a relatively high speed. This innovative strategy presents an attractive option for the development of crystal growth systems with superior characteristics.
Article
Chemistry, Multidisciplinary
Yifan Dang, Can Zhu, Motoki Ikumi, Masaki Takaishi, Wancheng Yu, Wei Huang, Xinbo Liu, Kentaro Kutsukake, Shunta Harada, Miho Tagawa, Toru Ujihara
Summary: An adaptive control method based on high-speed machine learning prediction models was proposed and applied to the solution growth of SiC crystals, ensuring consistently suitable growth conditions in an unsteady growth system with dynamic environmental changes. The hybrid of machine learning models and CFD simulation accelerated the entire design and optimization process significantly, leading to better growth performance.