• Title, Summary, Keyword: Vegard's law

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Energy-band-gap Variation of InxGaN1-x Thin Films with Indium Composition (인듐량에 따른 InxGaN1-x 박막의 에너지밴드갭 변화)

  • Park, Ki-Cheol;Ma, Tae-Young
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.22 no.8
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    • pp.677-681
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    • 2009
  • $In_xGa_{1-x}N$ alloys with 20-nm-thickness were deposited onto Mg:GaN/AlN/SiC substrates by MOCVD at $800\;^{\circ}C$. TMGa, TMIn and $NH_3$ were used as the precursor of gallium, indium and nitrogen, respectively. The mole ratio of indium in $In_xGa_{1-x}N$ films varied between 0 and 0.2. The energy-band-gaps of the films were obtained from the photoluminescence and cathodoluminescence peaks. The mole ratios of $In_xGa_{1-x}N$ films were calculated by applying Vegard's law to XRD results. The energy-band-gap versus indium composition plot for $In_xGa_{1-x}N$ alloys were well fit with a bowing parameter of 2.27.

Evolution of Metastable $L1_2-Al_3(Nb_xZr_{1-x})$ Phases in Rapidly Quenched Al-Nb-Zr Alloys

  • Park, Min-Woo
    • Journal of Korea Foundry Society
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    • v.27 no.6
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    • pp.250-254
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    • 2007
  • 3원계 Al-Nb-Zr의 용응 합금을 스프렛 ?봬?(splat-quenching) 방법을 이용하여 급속냉각응고 한 후, 응고된 시편을 698K에서 200시간까지 열처리하여 상전이를 연구하였다. 급속응고 및 열처리된 시편의 미세구조는 X-선 회절 및 투과전자 현미경으로 분석하였다. Al-1.95Nb-0.65Zr, Al-1.3Nb-1.3Zr, 및 Al-0.65Nb-1.95Zr (at%) 3원 합금계를 연구하였다. 각 합금의 조성은 Vegard's 법칙을 적용하여 Al(${\alpha}$)의 기지조직과 $L1_2-Al_3(Nb,Zr)$의 석출상들이 정합을 이루도록 선택되었다. 급속응고된 후 각 합금은 과고용된 Al(${\alpha}$)의 고용상을 형성하였다. Al-1.3Nb-1.3Zr, 및 Al-0.65Nb-1.95Zr의 급속응고된 상태의 시편을 698K에서 열처리하여 알루미늄 기지와 정합의 계면을 갖는 $L1_2-Al_3(Nb_{0.5}Zr_{0.5})$$L1_2-Al_3(Nb_{0.25}Zr_{0.75})$의 상을 각각 석출하였다. 반면 Al-1.95Nb-0.65Zr 합금은 평형상인 $D0_{22}-Al_3(Nb_{0.75}Zr_{0.25})$ 상을 석출하였다. 준안정상의 정합 $Al_3(Nb,Zr)$ 미세 분산상 석출은 입자의 조대화를 억제하고 재료의 고온 강도를 증가될 것으로 사료된다.

Application of Laser Beam Deflection Technique to Analysis of Stresses Generated during Hydrogen Diffusion through Pd Foil Electrode

  • Han Jeong-Nam;Pyun Su-Il
    • Journal of the Korean Electrochemical Society
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    • v.4 no.2
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    • pp.70-76
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    • 2001
  • The present work describes the capabilities of laser beam deflection (LBD) technique for the analysis of the stresses developed during hydrogen diffusion through Pd foil electrode. First, we explain briefly the elasto-diffusive (Gorsky effect) and diffusion-elastic phenomena. A model for the diffusion-elastic phenomenon is theoretically derived from the solution of the Fick's equation for given initial and boundary conditions, Vegard's second law and Hooke's law. Second, we introduce how to apply the principle of LBD technique to the study on the stresses generated during hydrogen diffusion. From the comparison of the deflection transients numerically calculated with those experimentally measured, we finally discuss the change in the tensile deflection with time in terms of hydrogen concentration profile transient and hydrogen diffusivity.

The recombination velocity at III-V compound heterojunctions with applications to Al/$_x$/Ga/$_1-x$/As-GaAs/$_1-y$/Sb/$_y$/ solar cells

  • 김정순
    • 전기의세계
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    • v.28 no.4
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    • pp.53-63
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    • 1979
  • Interface recombination velocity in $Al_{x}$G $a_{1-x}$ As-GaAs and $Al_{0.85}$, G $a_{0.15}$ As-GaA $s_{1-y}$S $b_{y}$ heterojunction systems is studied as a function of lattice mismatch. The results are applied to the design of highly efficient III-V heterojunction solar cells. A horizontal liquid-phase epitaxial growth system was used to prepare p-p-p and p-p-n $Al_{x}$G $a_{1-x}$ As-GaA $s_{1-y}$S $b_{y}$-A $l_{x}$G $a_{1-x}$ As double heterojunction test samples with specified values of x and y. Samples were grown at each composition, with different GaAs and GaAs Sb layer thicknesses. A method was developed to obtain the lattice mismatch and lattice constants in mixed single crystals grown on (100) and (111)B oriented GaAs substrates. In the AlGaAs system, elastic lattice deformation with effective Poisson ratios .mu.$_{eff}$ (100=0.312 and .mu.$_{eff}$ (111B) =0.190 was observed. The lattice constant $a_{0}$ (A $l_{x}$G $a_{1-x}$ As)=5.6532+0.0084x.angs. was obtained at 300K which is in good Agreement with Vegard's law. In the GaAsSb system, although elastic lattice deformation was observed in (111) B-oriented crystals, misfit dislocations reduced the Poisson ratio to zero in (100)-oriented samples. When $a_{0}$ (GaSb)=6.0959 .angs. was assumed at 300K, both (100) and (111)B oriented GaAsSb layers deviated only slightly from Vegard's law. Both (100) and (111)B zero-mismatch $Al_{0.85}$ G $a_{0.15}$As-GaA $s_{1-y}$S $b_{y}$ layers were grown from melts with a weight ratio of $W_{sb}$ / $W_{Ga}$ =0.13 and a growth temperature of 840 to 820 .deg.C. The corresponding Sb compositions were y=0.015 and 0.024 on (100) and (111)B orientations, respectively. This occurs because of a fortuitous in the Sb distribution coefficient with orientation. Interface recombination velocity was estimated from the dependence of the effective minority carrier lifetime on double-heterojunction spacing, using either optical phase-shift or electroluminescence timedecay techniques. The recombination velocity at a (100) interface was reduced from (2 to 3)*10$^{4}$ for y=0 to (6 to 7)*10$^{3}$ cm/sec for lattice-matched $Al_{0.85}$G $a_{0.15}$As-GaA $s_{0.985}$S $b_{0.015}$ Although this reduction is slightly less than that expected from the exponential relationship between interface recombination velocity and lattice mismatch as found in the AlGaAs-GaAs system, solar cells constructed from such a combination of materials should have an excellent spectral response to photons with energies over the full range from 1.4 to 2.6 eV. Similar measurements on a (111) B oriented lattice-matched heterojunction produced some-what larger interface recombination velocities.ities.ities.s.

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Microstructure and Magnetic Property of Nanostructured NiZn Ferrite Powder

  • Nam, Joong-Hee
    • Journal of the Korean Ceramic Society
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    • v.39 no.12
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    • pp.1119-1123
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    • 2002
  • Nanostructured spinel NiZn ferrites were prepared by the sol-gel method from metal nitrate raw materials. Analyses by X-ray diffraction and scanning electron microscopy showed the average particle size of NiZn ferrite was under 50 nm. The single phase of NiZn ferrites was obtained by firing at 250${\circ}C$, resulting in nanoparticles exhibiting normal ferrimagnetic behavior. The nanostructured $Ni_{1-X}Zn_XFe_2O_4$ (x=0.0∼1.0) were found to have the cubic spinel structure of which the lattice constants ${\alpha}_2$ increases linearly from 8.339 to 8.427 ${\AA}$ with increasing Zn content x, following Vegard's law, approximately. The saturation magnetization $M_s$ was 48 emu/g for x=0.4 and decreased to 8.0 emu/g for higher Zn contents suggesting the typical ferrimagnetism in mixed spinel ferrites. Pure NiZn ferrite phase substituted by Cu was observed before using the additive but hematite phase was partially appeared at $Ni_{0.2}Zn_{0.2}Cu_{0.6}Fe_2O_4$. On the other hand, the hematite phase in this NiZn Cu ferrite was disappeared after using the additive of acethyl aceton with small amount. The saturation magnetization Ms of $Ni_{0.2}Zn_{0.8-y}Cu_yFe_2O_4$(y=0.2∼0.6) as measured was about 51 emu/g at 77K and 19 emu/g at room temperature, respectively.

Perovskite-Like Strontium Titanium Zirconium Oxide Solid Solutions Prepared at Atmospheric Pressure

  • Choy, Jin-Ho;Kim, Ha-Suck;Kwon, Young-Uk;Kim Chong Hee
    • Bulletin of the Korean Chemical Society
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    • v.6 no.6
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    • pp.344-347
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    • 1985
  • Perovskite type oxides of $SrTiO_3,SrZrO_3,and\;SrTi_{1-x}Zr_xO_3$ have been systematically synthesized at $1250^{\circ}C$and $1550^{\circ}C$ with specimens containing additions of up to x=0.9 of zirconium by solid state reactions and characterized by X-ray diffraction. X-ray diffraction studies showed that the compound $SrTi_{1-x}Zr_xO_3$ has cubic structure. The lattice paramters of $SrTi_{1-x}Zr_xO_3$ solid solutions obey the Vegard's law and fairly large increase in volume can acompany the formation of this solution with increasing Zr content(X). Assuming the lattice constants of perovskite type compounds $A(B_{1-x}B'_x)O_3$where $B_{1-x}B'_x$ is $Ti_{1-x}Zr_x$, to be a linear function of the ionic radii of B and B' ions, the disordered ion pair of $Ti^{4+}$and $Zr^{4+}$ was verified from the lattice constants of a series compounds varying x=0,0.05, 0.25, 0.5, 0.75, 0.9, and 1.0 with known isovalent pairs.

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Variation of Dielectric Properties and Phase Stabilities with Substitution of A-Site in $Pb(Zn_{0.6}Mg_{0.4})_{1/3}Nb_{2/3}O_3$[PZMN] System ($Pb(Zn_{0.6}Mg_{0.4})_{1/3}Nb_{2/3}O_3$ [PZMN] 계에서 A-자리 치환에 따른 상안정화 및 유전 특성 변화)

  • 김봉철;김정주;김남경;조상희
    • Journal of the Korean Ceramic Society
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    • v.33 no.10
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    • pp.1131-1137
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    • 1996
  • The dielectric properties and phase stabilities of Pb(Zn0.6Mg0.4)1/3Nb2/3O3 [PZMN]system were investigated into substitution of A-site with Ba, Sr and Ca ions. The A-site substitutions led to the complexity of components of perovskite phase and then DPT coefficient increased. The A-site substitutions of Ba or Sr ion perovskite single phase could be easily formed by columbite process due to increase of perovskite phase stability. The variation of lattice parameters in specimen obeyed Vegard's law and curie temperature and dielectric constant of specimen decreased linearly. But Ca substitution led to perovskite phae instability. The lattice parameter dielectric constant and curie temperature of specimens drasticaly decreased with formation of pyrochlore phase.

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Crystal Structure Refinement and Persistent Luminescence Properties of Lu3Al5-xGaxO12:Ce3+,Cr3+ Phosphors (Lu3Al5-xGaxO12:Ce3+,Cr3+ 형광체의 결정구조 분석 및 잔광성 발광 특성)

  • Kim, Ji-Won;Kim, Yeong-Jin
    • Korean Journal of Materials Research
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    • v.30 no.8
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    • pp.413-420
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    • 2020
  • Lu3Al5-xGaxO12:Ce3+,Cr3+ powders are prepared using a solid-state reaction method. To determine the crystal structure, Rietveld refinement is performed. The results indicate that Ga3+ ions preferentially occupied tetrahedral rather than octahedral sites. The lattice constant linearly increases, obeying Vegard's law, despite the strong preference of Ga3+ for the tetrahedral sites. Increasing x led to a blue-shift of the Ce3+ emission band in the green region and a change in the emission intensity. Persistent luminescence is observed from the powders prepared with x = 2-3, occurring through a trapping and detrapping process between Ce3+ and Cr3+ ions. The longest persistent luminescence is achieved for x = 2; its lifetime is at least 30 min. The findings are explained using crystal structure refinement, crystal field splitting, optical band gap, and electron trapping mechanism.

Band Lineup Types Based on Ge1-xSnx/Ge1-ySny(001) (Ge1-xSnx/Ge1-ySny(001)의 band lineup 유형)

  • 박일수;전상국
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.15 no.9
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    • pp.770-775
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    • 2002
  • We present the band lineups of G $e_{1-}$x S $n_{x}$ G $e_{1-}$y S $n_{y(001)}$ heterostructures for the new devices. The energy gap of the bulk G $e_{1-}$x S $n_{x}$ alloy is calculated by taking into account the Vegard's law. The change of the energy gap due to the strain is understood in terms of the deformation Potential theory The valence band offset is obtained from the average bond energy model, where the changes of the band offset due to alloy compositions and strain are included. It is found that Ge/G $e_{1-}$y S $n_{y(001)}$ heterostructure has a staggered lineup type for 0$\leq$0.06 and a straddling one for 0.06$\leq$0.26. Meanwhile, Ge/G $e_{l-y}$ S $n_{y(001)}$ heterostructure has a staggered lineup type for 0$\leq$0.19 and a broken-gap one for 0.19$\leq$0.26. As a result, the various type of the G $e_{1-}$x S $n_{x}$ G $e_{1-}$y S $n_{y(001)}$ heterostructure can be applied for the useful device.evice.

ATOMIC MIGRATION IN MIXED FERRITE $Ni_{x}Co_{1-x}Fe_{2}O_{4}$

  • Lee, Seung-Wha;Park, Seung-Iel;Um, Young-Rang;Lee, Young-Jong;Kim, Sung-Baek;Kim, Chul-Sung
    • Journal of the Korean Magnetics Society
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    • v.5 no.5
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    • pp.778-781
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    • 1995
  • The mixed ferrite $Ni_{x}Co_{1-x}Fe_{2}O_{4}$ have been investigated by X-ray and $M\"{o}ssbauer$ spectoscpy. From the results of X-ray diffraction measurement the structure for this system is spinel, and the lattice constant is in accord with Vegard's law. $M\"{o}ssbauer$ spectra of $Ni_{x}Co_{1-x}Fe_{2}O_{4}$ have been taken at various temperature ranging from 13 to 800 K. The isomer shifts indicate that the valence states of the irons at both A(tetrahedral) and B(octahedral) sithe are found to be in ferric high-spin states. The variation of magnetic hyperfine fields at the A and B sites are explained on the basis on A-B and B-B supertransferred hyperfine interactions. It is found that Debye temperatures for the A and B sites of $CoFe_{2}O_{4}$ and $NiFe_{2}O_{4}$ are found to be ${\theta}_{A}=734{\pm}5K,\;{\theta}_{B}=248{\pm}5K,\;and\;{\theta}_{A}=378{\pm}5K,\;{\theta}_{B}=357{\pm}5K$, respectively. Atomic migration of $Ni_{0.3}Co_{0.7}Fe_{2}O_{4}$ starts near 450 K and increases rapidly with increasing temperature to such a degree that 61 % of the ferric ions at the A site have moved over to the B site by 700 K.

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