• Title, Summary, Keyword: crystal structure

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Mechanism of Piezoelectricity for Langasite Based on the Framework Crystal Structure

  • Ohsato, Hitoshi;Iwataki, Tsuyoshi;Morikoshi, Hiroki
    • Transactions on Electrical and Electronic Materials
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    • v.13 no.2
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    • pp.51-59
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    • 2012
  • Piezoelectric langasite crystals have superior properties such as high temperature performance and high quality Q and can be applied in combustion pressure sensors and surface acoustic wave (SAW) filters. Crystal growth, crystal structure and properties of langasite group are reviewed, and the mechanism of piezoelectricity of langasite is presented based on the crystal structure and deformation under high pressure. Finally, for the discovery of new piezoelectric materials, this paper presents the role of the framework, and recommends the search of framework crystal structure, because the characteristic of the mechanism exists on the framework of the crystal structure.

Annealing Effect with Various Ambient Conditions of ITO Thin Film (XPS와 XRD 분석을 이용한 ITO 박막의 결정성과 비정질 특성에 관한 연구)

  • Ko, Jung Whan;Jung, Bo Young;Oh, Teresa
    • Journal of the Semiconductor & Display Technology
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    • v.14 no.4
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    • pp.20-24
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    • 2015
  • This study was explained the correlation between the O 1s spectra and the crystallization of ITO thin films. The crystal structure of ITO thin films changed with various annealing temperatures and annealing methods such as atmosphere or vaccum conditions. The amorphous structure observed from XRD pattern showed the O 1s spectra with 531.2 eV, and the crystal structure of annealed ITO films analyzed by XRD pattern had the O 1s spectra of 529.8 eV as lower binding energy then the 531.2 eV. Oxygen in view of ITO films was related to the crystallization, and the ITO films annealed in an atmosphere pressure showed higher crystal structure than the ITO annealed in a vaccum. It was indicated that the amorphous structure had higher binding energy than the crystal structure analyzed by O 1s spectra of ITO films.

B20 Crystal Structure and Electromagnetic Property of MnGe and MnSi (B20 결정구조와 MnGe와 MnSi의 전자구조 및 자기적 특성)

  • Jeong, Tae Seong
    • Korean Journal of Materials Research
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    • v.29 no.8
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    • pp.477-482
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    • 2019
  • The magnetic properties and electronic structures of the B20 crystal structure MnGe and MnSi were investigated using the density functional theory with local density approximation. The low symmetry of the B20 crystal structure plays a very important role to make electromagnetic characteristics of these materials. The important result of the calculations is that it can be observed the appearance of a pair of gaps in the density of states near the Fermi level in both compounds. These features are results from d-band splitting by the low symmetry of the crystal field from B20 crystal structure. It can be seen that there is half-metallic characteristics from the density of states in both compounds. The calculation shows that the value of magnetic moment of MnGe is 5 times bigger than that of MnSi even though they have same crystal structure. The electronic structures of paramagnetic case have a very narrow indirect gap just above the Fermi level in both compounds. These gaps acquire some significance in establishing the stability of the ferromagnetic states within the local density approximation. Calculation shows that the Mn 3d character dominates the density of states near the Fermi level in both materials.

The Growth and Optical Properties of $MgGa_2Se_4$ Single Crystal ($MgGa_2Se_4$ 단결정의 성장과 광학적 특성)

  • 김형곤;이광석;이기형
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.25 no.4
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    • pp.402-406
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    • 1988
  • The MgGa2Se4 single crystal for study of optical properties is for the first time grown by Bridgmna method. The crystal structure of grown MgGa2Se4 single crystal has the Rhomobohedral structure (R3m) and its lattice constant are a=3.950\ulcorner c=38.893\ulcornerin Hexagonal structure. The energy band structure of grown MgGa2Se4 single crystal structure has direct band gap and the optical energy gap measured from optical absorption in this crystal is 2.20eV at 290K. The temperature dependence of energy gap was given Eg(T)=Eg(O)-aT\ulcorner)B+T), from varshni equation, where Eg(O)=2.34eV, a=8.79x10**-4eV/and b=250K.

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The Crystal and Molecular Structure of Thiamphenicol

  • Shin, Whan-chul;Kim, Sang-soo
    • Bulletin of the Korean Chemical Society
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    • v.4 no.2
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    • pp.79-83
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    • 1983
  • The structure of thiamphenicol, one of the congeners of chloramphenicol which is a well-known antibiotic, has been determined by single crystal x-ray diffraction techniques. The crystal structure was determined using diffractometer data obtained by the $2{\theta}:{\omega}$ scan technique with $MoK{\alpha}$ radiation from a crystal having space group symmetry $P2_{1}2_{1}2_{1}$, and unit cell parameters a = 5.779, b = 15.292 and c = 17.322 ${\AA}$ . The structure was solved by direct methods and refined by least squares to an R = 0.070 for the 2116 reflections. The overall V-shaped conformation of thiamphenicol revealed in this study is consistent with those from the crystallographic studies and the proposed models from the theoretical and nmr studies of chloramphenicol. However there is no intramolecular hydrogen bond and the propanediol moiety is fully extended in the thiamphenicol molecule, while the crystal structures of chloramphenicol show the existence of the hydrogen bond between the two hydroxyl groups of the propanediol moiety forming an acyclic ring. All of the thiamphenicol molecules in the crystal are linked by a threedimensional hydrogen bonding network.

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EFFECT OF METAL CONTACT ON THE CZT DETECTOR PERFORMANCE

  • Park, Se-Hwan;Park, Hyung-Sik;Lee, Jae-Hyung;Kin, Han-Soo;Ha, Jang-Ho
    • Journal of Radiation Protection and Research
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    • v.34 no.2
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    • pp.65-68
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    • 2009
  • Metal-semiconductor contact is very important for the operating property of semiconductor detector. $Cd_{0.96}$ $Zn_{0.04}$ Te semiconductor crystal was grown with Bridgman method, and the crystal was cut and polished. EPMA (Electron Probe Micro Analyzer) and ICP-MS (Inductively Coupled Plasma Mass Spectrometry) analysis were done to obtain the chemical composition and impurity of the crystal. Metal contact was deposited with thermal evaporator on both sides of the crystal. Detectors with Au/CZT/Au and In/CZT/Au structure were made, and I-V curve and the energy spectrum were measured with the detectors. It could be seen that the detector with the In/CZT/Au structure has superior property than the detector with Au/CZT/Au structure when the crystal resistivity was low. However, the metal contact structure effect becomes low when the crystal resistivity was high.

Crystal Structure and Characterization of a New Eight Coordinated Cadmium Complex

  • Hakimi, Mohammad;Moeini, Keyvan;Mardani, Zahra;Khorrami, Farzaneh
    • Journal of the Korean Chemical Society
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    • v.57 no.3
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    • pp.352-356
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    • 2013
  • In this work, a new cadmium complex $[Cd(L)(CH_3COO)_2].2H_2O$ (1) with the ligand L, N,N'-bis(2-pyridinecarboxalidene)-1,2-cyclohexanediamine was prepared and identified by elemental analysis, FT-IR, Raman, $^1H$ NMR spectroscopy and single-crystal X-ray diffraction. The cadmium atom in the crystal structure of 1 has distorted triangular dodecahedral geometry by coordination of the four nitrogen atoms of L and four oxygen atoms of the two acetate ions. Two water molecules are also incorporated in the crystal network. The $O-H{\cdots}O$ hydrogen bonds present in the crystal structure of 1. In this work, three structural surveys including coordination numbers of the cadmium atom, coordination modes of L and resonance in pyridine-2-ylmethanimine-based compounds are presented.

Development of Various Inorganic Crystal Structure Database Retrieval System (다양한 무기결정구조데이터베이스(ICSD) 검색 시스템 개발)

  • 김지영;이상호;한정민
    • Proceedings of the Korea Contents Association Conference
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    • pp.529-534
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    • 2004
  • KISTI has intended to provide domestic researchers of chemistry and materials with the Inorganic Crystal Structure Database free of charge. Therefore, we construct the database and develop new web-based information searching system with the use of the ICSD data licensed by the FIZ Karlsruhe, Germany. We organize several menus possible to search the structure of crystal in a variety of ways on the web and the search results show not only numerical data of the structure of crystal but also the graphic of X-ray diffraction pattern and the 3-dimension structure of crystal. The data will be updated continuously and the searching system will be improved in order to provide researchers with information easily and swiftly.

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Additional Damage of A17075-T651 under $90^{\circ}C$ Out-of phase Biaxial Loading from Crystal Structure Dependence ($90^{\circ}C$위상차의 이축하중 하에서 A17075-T651의 부가적 손상에 관한 결정구조 의존성에 관한 연구)

  • Lee, Hyun-Woo;Oh, Se-Jong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.1
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    • pp.104-111
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    • 1997
  • Accounting for the additional damages come out from non-proportional loading path effect, material damage according to crystal structure dependence was studied. Microscopic observations of damaged material by SEM(Scanning Electron Microscope) showed crystal structure dependence. Biaxial in-phase loaded specimens showed the slips of same direction, which pararell each other, but biaxial 90.deg. out-of-phase loaded specimens showed multiply crossed slips. S. H. Doong and D. F. Socie reported that wavy/planar or planar slip material showed the increase in the cyclic hardening level during non-proportional cycling. From these results, the additional hardening and non-proportional loading effects were related with slip mechanism, and the slip mechanism was related with crystal structure. In the present study, a damage mechanism which accounts for the non-proportional loading effect from crystal structure dependence was considered and applied to A17075-T651.

Crystal Structure and Piezoelectric Properties of Four Component Langasite A3B Ga3Si2O14 (A = Ca or Sr, B = Ta or Nb)

  • Ohsato, Hitoshi;Iwataki, Tsuyoshi;Morikoshi, Hiroki
    • Transactions on Electrical and Electronic Materials
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    • v.13 no.4
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    • pp.171-176
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    • 2012
  • As langasite $A_3BC_3D_2O_{14}$ compounds with piezoelectric properties exhibit no phase transition up to the melting point of 1,400-$1,500^{\circ}C$, many high temperature applications are expected for the SAW filter, temperature sensor, pressure sensor, and so on, based on the digital transformation of wider bandwidth and higher-bit rates. It has a larger electromechanical coupling factor compared to quartz and also nearly the same temperature stability as quartz. The $La_3Ga_5SiO_{14}$ (LGS) crystal with the $Ca_3Ga_2Ge_4O_{14}$-type crystal structure was synthesized and the crystal structure was analyzed by Mill et al. It is also an important feature that the growth of the single crystal is easy. In the case of three-element compounds such as $[R_3]_A[Ga]_B[Ga_3]_C[GaSi]_DO_{14}$ (R=La, Pr and Nd), the piezoelectric constant increases with the ionic radius of R. In this study, crystal structures of four-element compounds such as $[A_3]_A[B]_B[Ga_3]_C[Si_2]_DO_{14}$ (A = Ca or Sr, B = Ta or Nb) are analyzed by a single crystal X-ray diffraction, and the mechanism and properties of the piezoelectricity depending on the species of cation was clarified based on the crystal structure.