The Combined Influence of Gadolinium Doping and Non-stoichiometry on the Structural and Electrochemical Properties of Uranium Dioxide

Kim, Jandee,Lee, Jeongmook,Youn, Young-Sang,Liu, Nazhen,Kim, Jong-Goo,Ha, Yeong-Keong,Bae, Sang-Eun,Shoesmith, David W.,Kim, Jong-Yun Pergamon Press 2017 Electrochimica Acta Vol. No.

<P><B>Abstract</B></P> <P>The influence of Gd-doping level and oxygen stoichiometry on the structural properties and electrochemical reactivity of U<SUB>1−y</SUB>Gd<SUB>y</SUB>O<SUB>2±x</SUB> have been investigated. The stoichiometry of UO<SUB>2</SUB> matrices with different Gd contents was determined using the lattice parameter obtained by XRD. The extent of lattice contraction, defined by a contraction factor, was found to be dependent on the stoichiometry. The surface morphologies exhibited differences in grain size which varied with stoichiometry and its influence on the U atom diffusivity during fabrication. The differences in grain size and, hence, the density of grain boundaries was reflected in variations in electrical conductivity, with hyperstoichiometric specimens with a low number of boundaries, yielding an increase in conductivity with increasing Gd content. Cyclic voltammetry showed that a variation in Gd content had only a minor influence on the electrochemical reactivity of stoichiometric U<SUB>1−y</SUB>Gd<SUB>y</SUB>O<SUB>2</SUB>. By contrast, the reactivity of hypostoichiometric U<SUB>1−y</SUB>Gd<SUB>y</SUB>O<SUB>2−x</SUB> and hyperstoichiometric U<SUB>1−y</SUB>Gd<SUB>y</SUB>O<SUB>2+x</SUB> increased and decreased, respectively, with increasing Gd content. The formation of Gd-O<SUB>v</SUB> clusters in hyperstoichiometric U<SUB>1−y</SUB>Gd<SUB>y</SUB>O<SUB>2+x</SUB> has a more marked influence on reactivity than the accompanying changes in grain size and electrical conductivity.</P>

Oxygen stoichiometry controlled sharp insulator-metal transition in highly oriented VO2/TiO2 thin films

임지석,아눕,손민균,강대준,정상윤,이상한,조지영 한국물리학회 2018 Current Applied Physics Vol.18 No.6

The insulator-metal transition (IMT) in vanadium dioxide (VO2) which occurs above room temperature (67 °C) is highly sensitive to atomic defects caused by oxygen stoichiometry. The strained growth and the degree of oxygen deficiency in VO2 epitaxial films result in lowering of transition temperature below room temperature as well as the broadening of transition parameters such as transition width and hysteresis width, which limit its application potential. Here we demonstrate the growth of highly oriented strain-relaxed VO2 thin films on (001)-oriented TiO2 substrates at various oxygen partial pressures, exhibiting the narrow transition and hysteresis width. The cross-sectional transmission electron microscopy and x-ray diffraction analyses of the films reveal the highly oriented growth of insulating monoclinic VO2. The IMT parameters associated with temperature-dependent phase transition vary with the oxygen partial pressure used during the deposition. The presence of multiple and mixed valence states of vanadium in the films was confirmed by Raman and XPS analyses. We have achieved a narrow transition width (2.3 °C) and hysteresis width (1.2 °C) through controlling the oxygen stoichiometry during the growth of VO2/TiO2 films.

Oxygen stoichiometry controlled sharp insulator-metal transition in highly oriented VO₂/TiO₂ thin films

Im, Ji-Seok,Anoop, Gopinathan,Sohn, Min Kyun,Kang, Dae Joon,Jeong, Sang Yun,Lee, Sanghan,Jo, Ji Young ELSEVIER 2018 Current Applied Physics Vol.18 No.6

<P><B>Abstract</B></P> <P>The insulator-metal transition (IMT) in vanadium dioxide (VO<SUB>2</SUB>) which occurs above room temperature (67 °C) is highly sensitive to atomic defects caused by oxygen stoichiometry. The strained growth and the degree of oxygen deficiency in VO<SUB>2</SUB> epitaxial films result in lowering of transition temperature below room temperature as well as the broadening of transition parameters such as transition width and hysteresis width, which limit its application potential. Here we demonstrate the growth of highly oriented strain-relaxed VO<SUB>2</SUB> thin films on (001)-oriented TiO<SUB>2</SUB> substrates at various oxygen partial pressures, exhibiting the narrow transition and hysteresis width. The cross-sectional transmission electron microscopy and x-ray diffraction analyses of the films reveal the highly oriented growth of insulating monoclinic VO<SUB>2</SUB>. The IMT parameters associated with temperature-dependent phase transition vary with the oxygen partial pressure used during the deposition. The presence of multiple and mixed valence states of vanadium in the films was confirmed by Raman and XPS analyses. We have achieved a narrow transition width (2.3 °C) and hysteresis width (1.2 °C) through controlling the oxygen stoichiometry during the growth of VO<SUB>2</SUB>/TiO<SUB>2</SUB> films.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly oriented epitaxial VO<SUB>2</SUB> films were grown on (001)-oriented TiO<SUB>2</SUB> substrate. </LI> <LI> Insulator to metal transition (IMT) parameters of the VO<SUB>2</SUB> film varies with the oxygen stoichiometry. </LI> <LI> IMT in VO<SUB>2</SUB> varied depending on the degree of crystallinity and microstructure of the films. </LI> <LI> The VO<SUB>2</SUB> film grown at high deposition oxygen pressure showed a sharp transition with a narrow hysteresis width. </LI> </UL> </P>

Phase-controlled synthesis of SnO_x thin films by atomic layer deposition and post-treatment

Park, Bo-Eun,Park, Jaehong,Lee, Sangyoon,Lee, Sanghun,Kim, Woo-Hee,Kim, Hyungjun Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.480 No.-

<P><B>Abstract</B></P> <P>Tin oxide (SnO<SUB>x</SUB>) is a promising oxide semiconductor due to the distinct properties of n-type SnO<SUB>2</SUB> and p-type SnO based on its stoichiometry. However, the stoichiometry control of SnO<SUB>x</SUB> remains challenging due to the thermodynamic instability of SnO. In the study, we focus on establishing the controllable stoichiometry of SnO<SUB>x</SUB> via atomic layer deposition (ALD) and subsequent treatment. The controllable synthesis of SnO<SUB>2</SUB> and SnO is investigated by multiple analyses involving the chemical composition, crystal structure, and band structure. The ALD SnO<SUB>x</SUB> is composed mostly of Sn<SUP>4+</SUP> O bonds with intrinsic oxygen vacancies and is transformed into crystalline SnO<SUB>2</SUB> phase via post-annealing. The refractive index (~1.8) and optical bandgap energy (~3.6 eV) of ALD SnO<SUB>x</SUB> correspond to those of SnO<SUB>2</SUB>. Post-deposition treatment with H<SUB>2</SUB> plasma enables the effective transformation of SnO<SUB>2</SUB> into SnO due to the easy penetration of H<SUP>+</SUP> ion into the film and de-bonding of SnO via ion bombardment. The transformed SnO exhibits a significant amount of Sn<SUP>2+</SUP> O bonds with a refractive index of 2.8 and optical bandgap energy of ~2.9 eV. Specifically, the transformed SnO exhibits promise as an oxide semiconductor because it exhibits excellent stability with respect to re-oxidation into SnO<SUB>2</SUB> or further reduction into Sn metal. The present study advances practical applications that require a stable p-n junction through n-type SnO<SUB>2</SUB> and p-type SnO in various forms of device architectures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Formation of SnO<SUB>2</SUB> and SnO was controlled by atomic layer deposition and post-process. </LI> <LI> Chemical composition, crystal structure, and band structure of SnO<SUB>x</SUB> were analyzed. </LI> <LI> As-deposited SnO<SUB>x</SUB> exhibits typical characteristics of SnO<SUB>2</SUB>. </LI> <LI> Post-deposition treatment with H<SUB>2</SUB> plasma effectively transforms SnO<SUB>2</SUB> into SnO. </LI> <LI> Transformed SnO is stable against re-oxidation or reduction during post-process. </LI> </UL> </P>

국내 주요 강 생태계 내 동물플랑크톤의 탄소, 질소, 인 비율 해석

김현우 ( Hyun Woo Kim ),라긍환 ( Geung Hwan La ),정광석 ( Kwang Seuk Jeong ),김동균 ( Dong Kyun Kim ),황순진 ( Soon Jin Hwang ),이재용 ( Jaeyong Lee ),김범철 ( Bom Chul Kim ) 한국하천호수학회(구 한국육수학회) 2013 생태와 환경 Vol.46 No.4

The amounts of carbon (C), nitrogen (N) and phosphorus (P) in relation to dry weight (D.W.) were measured in zooplankton from the large four rivers (Han R., Geum R., Yeongsan R. and Seomjin R.) during 2004~2008. The stoichiometry of total zooplankton in four river systems was highly variable. The ranges of average C, N and P-contents were 70~620 mgC mg-1 D.W., 7.1~85.5 μgN mg-1 D.W. and 2.5~7.4 μgP mg-1 D.W., respectively. The mean C:N: P atomic ratios reflected large spatial differences. The C: P and N: P ratios of the zooplankton community ranged from 38 to 392: 1 and from 4 to 65: 1 in all sampling sites. Self- Organizing Map (SOM) was applied to the survey data, and the study sites were clearly classified into 3 clusters. Clustering was largely affected by the distribution pattern of C, N, P-contents, which is related with characteristics of river systems on the basis of stoichiometry.

Calculation of All Possible Stoichiometric Coefficients and Theoretical Yields of Microbial Global Reactions

Rafael Eduardo Hernández-Guisao,Aranda-Barradas Juan Silvestre,Badillo-Corona Agustín,García-Peña Elvia Inés,Salgado-Manjarrez Edgar 한국생물공학회 2022 Biotechnology and Bioprocess Engineering Vol.27 No.5

Stoichiometric analysis is a crucial step in biochemical processes because it allows us to find the proportions in which the substrates and products react. A system of algebraic equation is obtained from an elemental balance of the participating substances and determined, overdetermined or underdetermined systems can result depending on the number of substances and elements. Underdetermined systems are the most common ones as there are, generally, more substances than elemental balances. However, such systems have been poorly studied and a straightforward way to establish the solution space has not yet been reported. In this work a novel approach for finding all the possible solutions to such underdetermined systems is reported for the first time. The solutions space is expressed as a set of vectors which are here referred as extreme stoichiometries. To illustrate the general applicability and some uses of the proposed approach, three different fermentation systems are analyzed: growth of Chlamydomonas reinhardtii, a mixed culture for hydrogen production, and the growth of Saccharomyces cerevisiae. It is shown how the full stoichiometric spaces can be calculated for heterotrophy, autotrophy, mixotrophy, growth of mixed cultures in mixed substrates and how the experimental results should be contained in such spaces, what permits a consistency analysis. With the proposed method, it is now possible to estimate the maximum yields for any given microbial growth reaction and to assess the congruence of experimental data, even when the system is underdetermined.

PEM 단위 연료전지 가시화 셀을 이용한 당량비 변화에 따른 플러딩 현상에 관한 연구

남기훈(Ki Hoon Nam),변재기(Jae Ki Byun),최영돈(Young Don Choi) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.6

본 논문은 고분자 전해질 연료전지 공기극 유로 내부에서 당량비에 따라 발생하는 플러딩 현상을 가시화를 통해 확인하고, 전류 변화에 따른 물의 운송 특성에 관한 연구를 수행하였다. 공기극 당량비는 1.5, 2.0, 연료극 당량비는 1.5로 고정하여 실험을 수행하였다. 연료전지 공기측 당량비 2.0로 공급하였을 때 1.5와 비교하여 짧은 시간에 물이 생성되기 시작하였으며, 플러딩 영역이 빠르게 생성되는 결과가 나타났다. 또한, 공기극 당량비 1.5로 유지하는 경우 플러딩 영역 이후에 건조화 7.8A 이후 구간에서 건조화가 진행되며, 8A 이후구간에서 건조화가 시작되는 공기극 당량비 2.0에서 작동하는 연료전지와 비교하여 넓은 영역에서 물 생성이 활발하게 이루어져 MEA의 내구성과 수소이온전도도가 우수한 결과를 확인하였다. The objective of this paper is to demonstrate the cathode channel flooding effects at different stoichiometries in proton exchange membrane (PEM) fuel cells by using visualization techniques. The phenomena of liquid water formation and removal caused by current variations were also examined experimentally. Tests were conducted at cathode stoichiometries of 1.5 and 2.0, and the anode stoichiometry was fixed at 1.5. It is found that at an air-side stoichiometry of 2.0, liquid water begins to form and the flooding occurs faster than at an air-side stoichiometry of 1.5. Also, when the air-side stoichiometry of 1.5 is maintained, the dry-out phenomena is observed in the dry-out area 7.8 A following the field of flooding. Thus, a stoichiometry of 1.5 produced better performance in terms of membrane electrode assembly (MEA) durability and hydrogen ion conductivity than did a stoichiometry of 2.0, in which dry-out occurs beyond 8A.

Stoichiometry 변화에 따른 PEMFC내에서의 플러딩에 관한 실험적 연구

한성호(Han SeongHo),김경록(Kim KyoungRock),최영돈(Choi YoungDon) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

This is the experimental research that tries to explain a variety of stoichiometry is how to affect the performance and the flooding phenomenon of proton exchange membrane fuel cell. A value of stoichiometry changes to 1.2, 2.0 and 2.5 as its variation, either a temperature of cell changes to 50, 60 and 70. Into the comparison between theoretical and experimental value, this study analyzes that a variety of stoichiometry is how to affect flooding of cathode in the proton exchange membrane fuel cell. The effect of air stoichiometry, cell temperature, air humidity, different flow fields are also discussed in this paper. This study has accomplished the measurement of performance as the variety of stoichiometry in the cathode of proton exchange membrane fuel cell, moreover it has recorded the visualization of flooding in the cathode with a high-speed micro camera.

미생물 성장 특성에 기초한 독립영양탈질의 화학양론식 연구

이수원,김규동,최영균,김동한,정태학 대한상하수도학회 2004 상하수도학회지 Vol.18 No.2

It is necessary to supply external carbon source for enhancement of biological nitrogen removal from domestic wastewater with low influent C/N ratio. Sulfide was chosen as a cost effective electron donor and reaction stoichiometry for autotrophic denitrification was investigated by conducting bench-scale experiments in this study. Higher sulfur to nitrogen (S/N) ratio than the calculated value from theoretical reaction stoichiometry was required when the anoxic reactor was operated at open condition because dissolved oxygen introduced by surface aeration reacted with sulfide with ease. In addition, higher sulfate production and lower yield of microorganism could be observed under the same condition. It was possible to obtain reliable reaction stoichiometry for autotrophic denitrification by establishing pure anoxic condition. Linear relationship between bacterial growth and consumption of nitrate, sulfide, alkalinity, and sulfate production enabled to derive a relatively correct reaction stoichiometry for autotrophic denitrification when sulfide was used as an electron donor.

A-site Non-stoichiometry Effects on the Dielectric and the Piezoelectric Properties of Pb-free (Na_(0.50+x)Li_(0.03+y)K_(0.47))(Nb_(0.8)Ta_(0.2))O_3 Ceramics

김신웅,이태화,이정훈,성연수,조종호,송태권,김명호,M. S. Kim,J. S. Song 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.31

The effects of A-site non-stoichiometry were investigated in (Na_(0.50+x)Li_(0.03+y)K_(0.47))(Nb_(0.8)Ta_(0.2))O_3 (NLKNT) piezoelectric ceramics prepared by using a solid state reaction method. The content of Na was controlled to be -0.04 ≤ x ≤ +0.04 while the content of Li was controlled to be -0.02 ≤ y ≤ +0.02. A perovskite structure was maintained at all compositions although an impurity phase started forming in the case of x < 0 and y = 0. A polymorphic phase transition temperature between the orthorhombic and the tetragonal phases (T_(O−T)) was observed to vary with both Na and Li non-stoichiometry. The highest piezoelectric coefficient (d_(33)) of 200 pC/N was obtained in the case of x = 0 and y = +0.01, for which T_(O−T) was around room temperature.