[90] Iron-Based Layered Perovskite Oxyfluoride Electrocatalyst for Oxygen Evolution: Insights from Crystal Facets with Heteroanionic Coordination
Ryusuke Mizuochi, Yuuki Sugawara, Kengo Oka, Yoshiyuki Inaguma, Shunsuke Nozawa, Toshiyuki Yokoi, Takeo Yamaguchi, Kazuhiko Maeda
Journal of the American Chemical Society 146, 47, 32343–32355 2024年11月27日 [査読有り]

[89] Pressure-Induced YbFe2O4-Type to Spinel Structural Change of InGaMgO4
Takehiro Koike、Hena Das、Kengo Oka、Yoshihiro Kusano、Fernando Cubillas、Francisco Brown、Bojorqez Victor、Emmanuel Alvarez-Montano、Shigekazu Ito、 Kei Shigematsu、Hayato Togano、Ikuya Yamada、Hiroki Ishibashi、Yoshiki Kubota、Shigeo Mori、Noboru Kimizuka、Masaki Azuma
Solids 5(3), 422-433 2024年8月19日 [査読有り]

[88] Mechanism of intermetallic charge transfer and bond disproportionation in BiNiO3 and PbNiO3 revealed by hard x-ray photoemission spectroscopy
Tatsuya Yamaguchi、Mizuki Furo、Yuki Sakai、Takumi Nishikubo、Hajime Hojo、Masaki Azuma、Kengo Oka、Daisuke Mori、Yoshiyuki Inaguma、Masaichiro Mizumaki、Kento Yamamoto、Jan Kune、Takashi Mizokawa、Atsushi Hariki
Physical Review B 109, 205131 2024年5月13日 [査読有り]

[87]リバイスドローンペアーモデルで説明される6s電子と2p電子の相互作用によるバンドギャップの縮小と可視光応答光触媒特性の発現
岡 研吾、野間 直樹、岩崎 光伸
色材協会誌 96(5) 176-179 2023年5月20日 [査読有り]

[86] Compaction of α”-Fe16N2 particles by high-pressure treatment at several gigapascals
K. Oka、T. Ogawa、H. Yamamoto、C. Sakaguchi、R. Gallage、N. Kobayashi、M. Azuma
Scripta Materialia 229 115390-115390 2023年3月3日 [査読有り]

[85] Anionic ordering in Pb2Ti4O9F2 revisited by nuclear magnetic resonance and density functional theory
Kengo Oka、Tom Ichibha、Daichi Kato、Yasuto Noda、Yusuke Tominaga、Kosei Yamada、Mitsunobu Iwasaki、Naoki Noma、Kenta Hongo、Ryo Maezono、Fernando A. Reboredo
Dalton Transactions 51 15361-15369 2022年9月23日 [査読有り]

[84] 巨大負熱膨張材料の研究
東 正樹、岡 研吾、山本 孟、酒井 雄樹
粉体および粉末冶金 69(8) 356-361 2022年8月15日 [査読有り]

[83] Negative Thermal Expansion in Fluoroapatite Pb5(VO4)3F Enhanced by the Steric Effect of Pb2+
Kengo Oka、Miho Takasu、Wataru Nishiki、Takumi Nishikubo、Masaki Azuma、Naoki Noma、Mitsunobu Iwasaki
Inorganic Chemistry 61 12552-12558 2022年8月15日 [査読有り]

[82] Site preference of fluoride anion and potential ionic conductivity in fluorapatites A5(VO4)3F (A = Pb, Sr, and Ba)
Kengo Oka、Wataru Nishiki、Miho Takasu、Naoki Noma、Mitsunobu Iwasaki
Journal of the Ceramic Society of Japan 130(1) 35-38 2022年1月1日 [査読有り]

[81] A two-dimensional perovskite oxyfluoride Pb3Fe2O5F2 as a catalyst for electrochemical oxidation of water to oxygen
Ryusuke Mizuochi、Kengo Oka、Yoshiyuki Inaguma、Kazuhiko Maeda
Sustainable Energy & Fuels 6 2423-2427 2022年4月11日 [査読有り]

[80] Exploring novel functional properties arose from anion order in mixed anion compounds
Kengo OKA
Journal of the Ceramic Society of Japan 129(9) 555-560 2021年9月1日 [査読有り]

[79] Functional Transition Metal Perovskite Oxides with 6s2 Lone Pair Activity Stabilized by High-Pressure Synthesis
Masaki Azuma、Hajime Hojo、Kengo Oka、Hajime Yamamoto、Keisuke Shimizu、Kei Shigematsu、Yuki Sakai
Annual Review of Materials Research 51(1) 329-349 2021年7月26日 [査読有り]

[78] Improvement of a Pb2Ti2O5.4F1.2 Photoanode for Solar Water Splitting by Refining the Cocatalyst and Electrolyte
Kazuhiko Maeda、Naoki Hirayama、Hiroko Nakata、Kengo Oka
Bulletin of the Chemical Society of Japan 94(7) 1869-1874 2021年7月15日 [査読有り]

[77] Electrocatalytic activity of tetravalent FeCo mixed oxide for oxygen and hydrogen evolution reactions
Masaya Kinoshita、Ikuya Yamada、Shogo Kawaguchi、Kengo Oka、Shunsuke Yagi
Materials Transactions 61(8) 1507-1509 2020年8月1日 [査読有り]

[76] Negative Thermal Expansion in Lead-Free La-Substituted Bi0.5Na0.5VO3
Hayato Ishizaki、Yuki Sakai、Takumi Nishikubo、Zhao Pan、Kengo Oka、Hajime Yamamoto、Masaki Azuma
Chemistry of Materials 32(11) 4832-4837 2020年6月9日 [査読有り]

[75] Enhanced Catalytic Activity and Stability of the Oxygen Evolution Reaction on Tetravalent Mixed Metal Oxide
Ikuya Yamada、Masaya Kinoshita、Seiji Oda、Hirofumi Tsukasaki、Shogo Kawaguchi、Kengo Oka、Shigeo Mori、Hidekazu Ikeno、Shunsuke Yagi
Chemistry of Materials 32(9) 3893-3903 2020年5月12日 [査読有り]

[74] Activation of a Pt-loaded Pb2Ti2O5.4F1.2 photocatalyst by alkaline chloride treatment for improved H-2 evolution under visible light
Haruki Wakayama、Kosaku Kato、Kodai Kashihara、Tomoki Uchiyama、Akinobu Miyoshi、Hiroko Nakata、Daling Lu、Kengo Oka、Akira Yamakata、Yoshiharu Uchimoto、Kazuhiko Maeda
Journal of Materials Chemistry A 8(18) 9099-9108 2020年5月 [査読有り]

[73] Oxyfluoride Pb2Ti4O9F2 as a Stable Anode Material for Photoelectrochemical Water Oxidation
Kazuhiko Maeda、Naoki Hirayama、Hiroko Nakata、Haruki Wakayama、Kengo Oka
The Journal of Physical Chemistry C 124(3) 1844-1850 2020年1月23日 [査読有り]

[72] 圧力誘起相転移を利用した巨大負熱膨張物質の開発
東 正樹, 酒井 雄樹, 西久保 匠, 岡 研吾, 山本 孟
高圧力の科学と技術 30(3) 187-194 2020年 [査読有り]

[71] Light Absorption Properties and Electronic Band Structures of Lead-Vanadium Oxyhalide Apatites Pb5(VO4)3X (X = F, Cl, Br, I)
Masashi Nakamura、Kenji Oqmhula、Keishu Utimula、Miharu Eguchi、Kengo Oka、Kenta Hongo、Ryo Maezono、Kazuhiko Maeda
Chemistry - An Asian Journal 15(4) 540-545 2020年1月 [査読有り]

[70] Enhanced Negative Thermal Expansion Induced by Simultaneous Charge Transfer and Polar-Nonpolar Transitions
Takumi Nishikubo、Yuki Sakai、Kengo Oka、Tetsu Watanuki、Akihiko Machida、Masaichiro Mizumaki、Koki Maebayashi、Takashi Imai、Takahiro Ogata、Keisuke Yokoyama、Yoichi Okimoto、Shin-ya Koshihara、Hajime Hojo、Takashi Mizokawa、Masaki Azuma
Journal of the American Chemical Society 141(49) 19397-19403 2019年11月 [査読有り]

[69] Solar-Driven Photoelectrochemical Water Oxidation over an n-Type Lead Titanium Oxyfluoride Anode
Hirayama Naoki、Nakata Hiroko、Wakayama Haruki、Nishioka Shunta、Kanazawa Tomoki、Kamata Ryutaro、Ebato Yosuke、Kato Kosaku、Kumagai Hiromu、Yamakata Akira、Oka Kengo、Maeda Kazuhiko
Journal of the American Chemical Society 141(43) 17158-17165 2019年10月30日 [査読有り]

[68] High-pressure synthesis of highly oxidized Ba0.5Sr0.5Co0.8Fe0.2O3-delta cubic perovskite
Yamada Ikuya、Odake Takao、Asai Kaisei、Oka Kengo、Kawaguchi Shogo、Wada Kouhei、Yagi Shunsuke
Materials Chemistry Frontiers 3(6) 1209-1217 2019年6月1日 [査読有り]

[67] 相転移型巨大負熱膨張物質
東正樹、岡研吾、山本孟、酒井雄樹
応用物理 88(3) 185‐188 2019年3月10日 [査読有り]

[66] Negative thermal expansion in electron doped PbVO3-xFx
Ogata Takahiro、Oka Kengo、Azuma Masaki
Applied Physics Express 12(2) 023005 2019年2月 [査読有り]

[65] 金属フッ化物 アニオンが秩序配列した酸フッ化物の創製とその機能
岡研吾
セラミックス 54(9) 625-628 2019年 [査読有り]

[64] Pronounced Negative Thermal Expansion in Lead-Free BiCoO3-Based Ferroelectrics Triggered by the Stabilized Perovskite Structure
Zhao Pan、Xingxing Jiang、Takumi Nishikubo、Yuki Sakai、Hayato Ishizaki、Kengo Oka、Zheshuai Lin、Masaki Azuma
Chemistry of Materials 31 6187-6192 2019年1月1日 [査読有り]

[63] High-pressure synthesis of highly oxidized Ba0.5Sr0.5Co0.8Fe0.2O3−δ cubic perovskite
Ikuya Yamada、Takao Odake、Kaisei Asai、Kengo Oka、Shogo Kawaguchi、Kouhei Wada、Shunsuke Yagi
Materials Chemistry Frontiers 3 1209-1217 2019年 [査読有り]

[62] Light Absorption Properties and Electronic Band Structures of Lead Titanium Oxyfluoride Photocatalysts Pb2Ti4O9F2 and Pb2Ti2O5.4F1.2
Haruki Wakayama、Keishu Utimula、Tom Ichibha、Ryo Kuriki、Kenta Hongo、Ryo Maezono、Kengo Oka、Kazuhiko Maeda
The Journal of Physical Chemistry C 122(46) 26506-26511 2018年11月22日 [査読有り]

[61] Development of Bismuth Ferrite as a Piezoelectric and Multiferroic Material by Cobalt Substitution
H. Hojo、K. Oka、K. Shimizu、H. Yamamoto、R. Kawabe、M. Azuma
Advanced Materials 30(33) 1705665 2018年8月16日 [査読有り]

[60] Incorporation of sulfur ions into La2−xSrxCuO4 superconducting cuprate
Kengo Oka、Kensuke Shirota、Yoshiki Sato、Katsuyoshi Oh-ishi
Journal of Asian Ceramic Societies 6(3) 284-288 2018年7月3日 [査読有り]

[59] Optimized negative thermal expansion induced by gradual intermetallic charge transfer in Bi1− x Sb x NiO3
Takumi Nishikubo、Yuki Sakai、Kengo Oka、Masaichiro Mizumaki、Tetsu Watanuki、Akihiko Machida、Naoyuki Maejima、Shigenori Ueda、Takashi Mizokawa、Masaki Azuma
Applied Physics Express 11(6) 061102-061102 2018年5月10日 [査読有り]

[58] A Stable, Narrow-Gap Oxyfluoride Photocatalyst for Visible-Light Hydrogen Evolution and Carbon Dioxide Reduction
Ryo Kuriki、Tom Ichibha、Kenta Hongo、Daling Lu、Ryo Maezono、Hiroshi Kageyama、Osamu Ishitani、Kengo Oka、Kazuhiko Maeda
Journal of the American Chemical Society 140(21) 6648-6655 2018年5月7日 [査読有り]

[57] Synthesis, Crystal Structure, and Optical Properties of Layered Perovskite Scandium Oxychlorides: Sr2ScO3Cl, Sr3Sc2O5Cl2, and Ba3Sc2O5Cl2
Yu Su、Yoshihiro Tsujimoto、Kotaro Fujii、Makoto Tatsuta、Kengo Oka、Masatomo Yashima、Hiraku Ogino、Kazunari Yamaura
Inorganic Chemistry 57(9) 5615-5623 2018年5月7日 [査読有り]

[56] Experimental and theoretical studies of the metallic conductivity in cubic PbVO3 under high pressure
Kengo Oka、Touru Yamauchi、Sudipta Kanungo、Taku Shimazu、Katsuyohi Oh-ishi、Yoshiya Uwatoko、Masaki Azuma、Tanusri Saha-Dasgupta
Journal of the Physical Society of Japan 87(2) 024801 2018年 [査読有り]

[55] Systematic charge distribution changes in Bi- and Pb-3d transition metal perovskites
Masaki Azuma、Yuki Sakai、Takumi Nishikubo、Masaichiro Mizumaki、Tetsu Watanuki、Takashi Mizokawa、Kengo Oka、Hajime Hojo、Makoto Naka
Dalton Transactions 47(5) 1371-1377 2018年 [査読有り]

[54] Ultrafast Control of the Polarity of BiCoO3 by Orbital Excitation as Investigated by Femtosecond Spectroscopy
Y. Okimoto、S. Naruse、R. Fukaya、T. Ishikawa、S. Koshihara、K. Oka、M. Azuma、K. Tanaka、H. Hirori
Physical Review Applied 7(6) 064016 2017年6月12日 [査読有り]

[53] Analysis of CO2 absorption reaction of Li4SiO4 on the basis of madelung potential of Li site in crystal structure
Katsuyoshi Oh-Ishi、Ryota Kobayashi、Kengo Oka
Journal of the Ceramic Society of Japan 125(5) 383-386 2017年5月 [査読有り]

[52] Hydrothermal Synthesis, Structure, and Superconductivity of Simple Cubic Perovskite (Ba0.62K0.38)(Bi0.92Mg0.08)O-3 with T-c similar to 30 K
Mirza H. K. Rubel、Takahiro Takei、Nobuhiro Kumada、M. Mozahar Ali、Akira Miura、Kiyoharu Tadanaga、Kengo Oka、Masaki Azuma、Eisuke Magome、Chikako Moriyoshi、Yoshihiro Kuroiwa
Inorganic Chemistry 56(6) 3174-3181 2017年3月 [査読有り]

[51] A-Site and B-Site Charge Orderings in an s-d Level Controlled Perovskite Oxide PbCoO3
Yuki Sakai、Junye Yang、Runze Yu、Hajime Hojo、Ikuya Yamada、Ping Miao、Sanghyun Lee、Shuki Torii、Takashi Kamiyama、Marjana Lezaic、Gustav Bihlmayer、Masaichiro Mizumaki、Jun Komiyama、Takashi Mizokawa、Hajime Yamamoto、Takumi Nishikubo、Yuichiro Hattori、Kengo Oka、Yunyu Yin、Jianhong Dai、Wenmin Li、Shigenori Ueda、Akihisa Aimi、Daisuke Mori、Yoshiyuki Inaguma、Zhiwei Hu、Takayuki Uozumi、Changqing Jin、Youwen Long、Masaki Azuma
Journal of the American Chemical Society 139(12) 4574-4581 2017年3月 [査読有り]

[50] Preparation of Mo-Re-C samples containing Mo7Re13C with the beta-Mn-type structure by solid state reaction of planetary-ball-milled powder mixtures of Mo, Re and C, and their crystal structures and superconductivity
Katsuyoshi Oh-ishi、Kenta Nagumo、Kazuya Tateishi、TakafumiOhnishi、Kenta Yoshikane、Machiko Sugiyama、Kengo Oka、Ryota Kobayashi
Journal of Solid State Chemistry 245 207-212 2017年1月 [査読有り]

[49] 放射光で解き明かすサイト間電荷移動誘起巨大負熱膨張
岡研吾、東正樹
放射光 29(5) 245‐252 2016年9月30日 [査読有り]

[48] Glassy Distribution of Bi3+/Bi5+ in Bi1−xPbxNiO3 and Negative Thermal Expansion Induced by Intermetallic Charge Transfer
K. Nakano、K. Oka、T. Watanuki、M. Mizumaki、A. Machida、A. Agui、H. Kim、J. Komiyama、T. Mizokawa、T. Nishikubo、Y. Hattori、S. Ueda、Y. Sakai、M. Azuma
Chemistry of Materials 28(17) 6062-6067 2016年9月 [査読有り]

[47] Temperature-Independent, Large Dielectric Constant Induced by Vacancy and Partial Anion Order in the Oxyfluoride Pyrochlore Pb2Ti2O6−δF2δ
Kengo Oka、Hajime Hojo、Masaki Azuma、Katsuyoshi Oh-ishi
Chemistry of Materials 28(15) 5554-5559 2016年8月 [査読有り]

[46] Spin Structure Change in Co-Substituted BiFeO3
Hajime Yamamoto、Takumi Kihara、Kengo Oka、Masashi Tokunaga、Ko Mibu、Masaki Azuma
Journal of the Physical Society of Japan 85(6) 064704 2016年6月 [査読有り]

[45] High-Pressure Polymorph of NaBiO3
Octavianti Naa、Nobuhiro Kumada、Akira Miura、Takahiro Takei、Masaki Azuma、Yoshihiro Kusano、Kengo Oka
Inorganic Chemistry 55(12) 5747-5749 2016年6月 [査読有り]

[44] High-Temperature Monoclinic Cc Phase with Reduced c/a Ratio in Bi-based Perovskite Compound Bi2ZnTi1−xMnxO6
Runze Yu、Narumi Matsuda、Ken Tominaga、Keisuke Shimizu、Hajime Hojo、Yuki Sakai、Hajime Yamamoto、Kengo Oka、Masaki Azuma
Inorganic Chemistry 55(12) 6124-6129 2016年6月 [査読有り]

[43] Hydrothermal Synthesis, Crystal Structure, and Superconductivity of a Double-Perovskite Bi Oxide
Mirza H. K. Rubel、Takahiro Takei、Nobuhiro Kumada、M. Mozahar Ali、Akira Miura、Kiyoharu Tadanaga、Kengo Oka、Masaki Azuma、Masatomo Yashima、Kotaro Fujii、Eisuke Magome、Chikako Moriyoshi、Yoshihiro Kuroiwa、James R. Hester、Maxim Aydeev
Chemistry of Materials 28(2) 459-465 2016年1月 [査読有り]

[42] Pb・Biを含むベロブスカイト型酸化物の高圧合成と構造、物性
岡 研吾
高圧力の科学と技術 26(2) 178-188 2016年 [査読有り]

[41] Observation of Anion Order in Pb2Ti4O9F2
Kengo Oka、Katsuyoshi Oh-ishi
Inorganic Chemistry 54(21) 10239-10242 2015年11月

[40] Melting of Pb Charge Glass and Simultaneous Pb-Cr Charge Transfer in PbCrO3 as the Origin of Volume Collapse
Runze Yu、Hajime Hojo、Tetsu Watanuki、Masaichiro Mizumaki、Takashi Mizokawa、Kengo Oka、Hyunjeong Kim、Akihiko Machida、Kouji Sakaki、Yumiko Nakamura、Akane Agui、Daisuke Mori、Yoshiyuki Inaguma、Martin Schlipf、Konstantin Z. Rushchanskii、Marjana Lezaic、Masaaki Matsuda、Jie Ma、Stuart Calder、Masahiko Isobe、Yuichi Ikuhara、Masaki Azuma
Journal of the American Chemical Society 137(39) 12719-12728 2015年10月 [査読有り]

[39] Differences in local structure around Co and Fe of the BiCo1−xFexO3 system determined by x-ray absorption fine structure
N. Ishimatsu、T. Watanabe、K. Oka、M. Azuma、M. Mizumaki、K. Nitta、T. Ina、N. Kawamura
Physical Review B 92(5) 054108 2015年8月 [査読有り]

[38] Hydrothermal synthesis of a new Bi-based (Ba0.82K0.18)(Bi0.53Pb0.47)O3 superconductor
Mirza H.K. Rubel Takahiro Takei Nobuhiro Kumada M.M. Ali Akira Miura Kiyoharu Tadanaga K. Oka M. Azuma E. Magomae C. Moriyoshi Y. Kuroiwa
Journal of Alloys and Compounds 634(15) 208-214 2015年6月1日 [査読有り]

[37] Negative thermal expansion induced by intermetallic charge transfer
Masaki Azuma、Kengo Oka、Koichiro Nabetani
Science and Technology of Advanced Materials 16(3) 034904 2015年6月 [査読有り]

[36] New PbTiO3-Type Giant Tetragonal Compound Bi2ZnVO6 and Its Stability under Pressure
Runze Yu、Hajime Hojo、Kengo Oka、Tetsu Watanuki、Akihiko Machida、Keisuke Shimizu、Kiho Nakano、Masaki Azuma
Chemistry of Materials 27(6) 2012-2017 2015年3月 [査読有り]

[35] Suppression of temperature hysteresis in negative thermal expansion compound BiN1−xFexO3 and zero-thermal expansion composite
K. Nabetani、Y. Muramatsu、K. Oka、K. Nakano、H. Hojo、M. Mizumaki、A. Agui、Y. Higo、N. Hayashi、M. Takano、M. Azuma
Applied Physics Letters 106(6) 061912 2015年2月 [査読有り]

[34] Superconductivity in Noncentrosymmetric Iridium Silicide Li2IrSi3
Sunseng Pyon、Kazutaka Kudo、Jun-ichi Matsumura、Hiroyuki Ishii、Genta Matsuo、Minoru Nohara、Hajime Hojo、Kengo Oka、Masaki Azuma、V. Ovidiu Garlea、Katsuaki Kodama、Shin-ichi Shamoto
Journal of the Physical Society of Japan 83(9) 093706 2014年9月 [査読有り]

[33] High-pressure synthesis of BaVO3: A new cubic perovskite
Kousuke Nishimura、Ikuya Yamada、Kengo Oka、Yuichi Shimakawa、Masaki Azuma
Journal of Physics and Chemistry of Physics 75(6) 710-712 2014年6月 [査読有り]

[32] Superconducting Double Perovskite Bismuth Oxide Prepared by a Low-Temperature Hydrothermal Reaction
Mirza H. K. Rubel、Akira Miura、Takahiro Takei、Nobuhiro Kumada、M. Mozahar Ali、Masanori Nagao、Satoshi Watauchi、Isao Tanaka、Kengo Oka、Masaki Azuma、Eisuke Magome、Chikako Moriyoshi、Yoshihiro Kuroiwa、A. K. M. Azharul Islam
Angewandte Chemie International Edition 53(14) 3599-3603 2014年4月 [査読有り]

[31] BiNi1‐xFexO3 のサイト間電荷移動誘起負の熱膨張における温度履歴の抑制
奈部谷光一郎、岡研吾、東正樹
粉体および粉末冶金 61(1) 35-38 2014年 [査読有り]

[30] 巨大な負の熱膨張を示すペロブスカイトBiNiO3 を用いたゼロ熱膨張コンポジットの作製
村松裕也、奈部谷光一郎、岡研吾、東正樹
粉体および粉末冶金 61(1) 39-43 2014年 [査読有り]

[29] Spin Frustration from cis-Edge or -Corner Sharing Metal-Centered Octahedra
Romain Gautier、Kengo Oka、Takumi Kihara、Nitesh Kumar、Athinarayanan Sundaresan、Masashi Tokunaga、Masaki Azuma、Kenneth R. Poeppelmeier
Journal of the American Chemical Society 135(51) 19268-19274 2013年12月10日 [査読有り]

[28] Crystal and magnetic structure in Co-substituted BiFeO3
Izabela Sosnowska、Masaki Azuma、Radosław Przeniosło、Dariusz Wardecki、Wei-Tin Chen、Kengo Oka、Yuichi Shimakawa
Inorganic Chemistry 52(22) 13269-13277 2013年11月18日 [査読有り]

[27] BiCo1-xFexO3の分極回転現象
岡研吾、東正樹、森茂生
日本結晶学会誌 55(5) 278-284 2013年10月31日 [査読有り]

[26] Direct observation of negative thermal expansion in SrCu3Fe4O12
Ikuya Yamada、Kentaro Shiro、Kengo Oka、Masaki Azuma、Tetsuo Irifune
Journal of the Ceramic Society of Japan 121(1418) 912-914 2013年10月 [査読有り]

[25] Structure and Magnetic Properties of BiFe1–xCoxO3 and Bi0.9Sm0.1Fe1–xCoxO3
Makoto Kubota、Kengo Oka、Hisato Yabuta、Kaoru Miura、 Masaki Azuma
Inorganic Chemistry 52, 18, 10698–10704 (2013) 2013年9月 [査読有り]

[24] The Thermal Transformation Arrest Phenomenon in NiCoMnAl Heusler Alloys
Xiao Xu、Wataru Ito、Masashi Tokunaga、Takumi Kihara、Kengo Oka、Rie Umetsu、Takeshi Kanomata、Ryosuke Kainuma
Metals 3(3) 298-311 2013年8月22日 [査読有り]

[23] Tuning negative thermal expansion in Bi(1-x)Ln(x)NiO(3) (Ln = La, Nd, Eu, Dy)
Kengo Oka、Koichiro Nabetani、Chika Sakaguchi、Hayato Seki、Michal Czapski、Yuichi Shimakawa、Masaki Azuma
Applied Physics Letters 103(6) 061909 2013年8月 [査読有り]

[22] Intermetallic charge-transfer transition in Bi1-xLa xNiO3 as the origin of the colossal negative thermal expansion
Kengo Oka、Masaichiro Mizumaki、Chika Sakaguchi、Alexandra Sinclair、Clemens Ritter、J. Paul Attfield、Masaki Azuma
Physical Review B 88(1) 014112 2013年7月29日 [査読有り]

[21] ぺロブスカイトBiNiO3におけるサイト間電荷移動と巨大負の熱膨張
東正樹、岡研吾
日本結晶学会誌 54(6) 325-331 2012年12月31日 [査読有り]

[20] Magnetic ground state of the frustrated honeycomb lattice antiferromagnet Bi3Mn4O12(NO3)
N. Onishi、K. Oka、M. Azuma、Y. Shimakawa、Y. Motome、T. Taniguchi、M. Hiraishi、M. Miyazaki、T. Masuda、A. Koda、K. M. Kojima、R. Kadono
Physical Review B 85(18) 184412 2012年5月 [査読有り]

[19] Sm置換BiFeO3の相転移挙動
久保田 純、岡 研吾、中村 嘉孝、薮田 久人、三浦 薫、島川 祐一、東 正樹
粉体および粉末冶金 59(5) 239-245 2012年5月 [査読有り]

[18] Crystal Structural, Magnetic, and Transport Properties of Layered Cobalt Oxyfluorides, Sr2CoO3+xF1-x (0 <= x <= 0.15)
Yoshihiro Tsujimoto、Clastin I. Sathish、Kun-Pyo Hong、Kengo Oka、Masaki Azuma、Yanfeng Guo、Yoshitaka Matsushita、Kazunari Yamaura、Eiji Takayama-Muromachi
Inorganic Chemistry 51(8) 4802-4809 2012年4月 [査読有り]

[17] Polarization Rotation in the Monoclinic Perovskite BiCo1-xFexO3
Kengo Oka、Tsukasa Koyama、Tomoatsu Ozaaki、Shigeo Mori、Yuichi Shimakawa、Masaki Azuma
Angewandte Chemie International Edition 51(32) 7977-7980 2012年 [査読有り]

[16] Structural Transformation of Hexagonal (0001)BaTiO3 Ceramics to Tetragonal (111)BaTiO3 Ceramics
Takayuki Watanabe、Mikio Shimada、Toshiaki Aiba、Hisato Yabuta、Kaoru Miura、Kengo Oka、Masaki Azuma、Satoshi Wada、Nobuhiro Kumada
Japanese Journal of Applied Physics 50(9) 09ND01 2011年9月 [査読有り]

[15] Sequential Phase Transitions in Sm Substituted BiFeO3
Makoto Kubota、Kengo Oka、Yoshitaka Nakamura、Hisato Yabuta、Kaoru Miura、Yuichi Shimakawa、Masaki Azuma
Japanese Journal of Applied Physics 50(9) 09NE08 2011年9月 [査読有り]

[14] Co-O-O-Co superexchange pathways enhanced by small charge-transfer energy in multiferroic BiCoO3
T. Sudayama、Y. Wakisaka、T. Mizokawa、H. Wadati、G. A. Sawatzky、D. G. Hawthorn、T. Z. Regier、K. Oka、M. Azuma、Y. Shimakawa
Physical Review B 83(23) 235105 2011年6月 [査読有り]

[13] Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer
Masaki Azuma、Wei-tin Chen、Hayato Seki、Michal Czapski、Smirnova Olga、Kengo Oka、Masaichiro Mizumaki、Tetsu Watanuki、Naoki Ishimatsu、Naomi Kawamura、Shintaro Ishiwata、Matthew G. Tucker、Yuichi Shimakawa、J. Paul Attfield
Nature Communications 2 347-351 2011年6月 [査読有り]

[12] Pressure-Induced Spin-State Transition in BiCoO3
Kengo Oka、Masaki Azuma、Wei-tin Chen、Hitoshi Yusa、Alexei A. Belik、Eiji Takayama-Muromachi、Masaichiro Mizumaki、Naoki Ishimatsu、Nozomu Hiraoka、Masahiko Tsujimoto、Matthew G. Tucker、J. Paul Attfield、Yuichi Shimakawa
Journal of the American Chemical Society 132(27) 9438-9443 2010年7月 [査読有り]

[11] Intermetallic Charge Transfer in A-Site-Ordered Double Perovskite BiCu3Fe4O12
Youwen Long、Takashi Saito、Takenori Tohyama、Kengo Oka、Masaki Azuma、Yuichi Shimakawa
Inorganic Chemistry 48(17) 8489-8492 2009年9月 [査読有り]

[10] Effect of Zn substitution for Cu on Ca2-xNaxCuO2Cl2 near the hole concentration of 1/8 per Cu
Kohki H. Satoh、Masatoshi Hiraishi、Masanori Miyazaki、Soshi Takeshita、Akihiro Koda、Ryosuke Kadono、Ikuya Yamada、Kengo Oka、Masaki Azuma、Yuichi Shimakawa、Mikio Takano
Physica B 404(5-7) 713-716 2009年4月 [査読有り]

[9] Pressure-Induced Transformation of 6H Hexagonal to 3C Perovskite Structure in PbMnO3
Kengo Oka、Masaki Azuma、Shigeto Hirai、Alexei A. Belik、Hiroshi Kojitani、Masaki Akaogi、Mikio Takano、Yuich Shimakawa
Inorganic Chemistry 48(5) 2285-2288 2009年3月 [査読有り]

[8] Hydrothermal Synthesis of a New Double Perovskite-Type Bismuthate, (Ba0.75K0.14H0.11)BiO3•nH2O
Hong Jiang、Nobuhiro Kumada、Yoshinori Yonesaki、Takahiro Takei、Nobukazu Kinomura、Masatorno Yashima、Masaki Azuma、Kengo Oka、Yuichi Shimakawa
Japanese Journal of Applied Physics 48(1) 010216 2009年1月 [査読有り]

[7] Rhombohedral-tetragonal phase boundary with high curie temperature in (1-x)BiCoO3-xBiFeO3 solid solution
Masaki Azuma、Seiji Niitaka、Naoaki Hayashi、Kengo Oka、Mikio Takano、Hiroshi Funakubo、Yuichi Shimakawa
Japanese Journal of Applied Physics 47(9) 7579-7581 2008年9月19日 [査読有り]

[6] Magnetic Ground-State of Perovskite PbVO3 with Large Tetragonal Distortion
Kengo Oka、Ikuya Yamada、Masaki Azuma、Soshi Takeshita、Kohki H. Satoh、Akihiro Koda、Ryosuke Kadono、Mikio Takano、Yuichi Shimakawa
Inorganic Chemistry 47(16) 7355-7359 2008年8月 [査読有り]

[5] Charge and magnetic orderings in the triangular-lattice antiferromagnet InFe2O4
Kengo Oka、Masaki Azuma、Naaki Hayashi、Shigetoshi Muranaka、Yasuo Narumi、Koichi Kindo、Shinya Ayukawa、Masatsune Kato、Yoji Koike、Yuichi Shimakawa、Mikio Takano
Journal of the Physical Society of Japan 77(6) 064803 2008年6月 [査読有り]

[4] Bi，Pb-3d遷移金属ペロブスカイトの構造物性研究
東正樹、岡研吾、辻本将彦、齊藤高志、磯田正二、島川祐一、高野幹夫、新高誠司、BELIK Alexei、石渡晋太郎
日本結晶学会誌 49(6) 335-340 2007年12月25日 [査読有り]

[3]三角格子反強磁性体ＩｎＦｅ２Ｏ４の合成と物性
岡 研吾、東 正樹、鳴海 康雄、金道 浩一、林 直顕、島川 祐一、高野 幹夫
粉体および粉末冶金 54(1) 53-57 2007年 [査読有り]

[2] Active state of tungsten oxides on WO3/ZrO2 catalyst for steam reforming of dimethyl ether combined with CuO/CeO2
Kengo Oka、Toshiya Nishiguchi、Hiroyoshi Kanai、Kazunori Utani、Seiichiro Imamura
Applied Catalysis A: General 309(2) 187-191 2006年8月 [査読有り]

[1] Durability of WO3/ZrO2–CuO/CeO2 catalysts for steam reforming of dimethyl ether
Toshiya Nishiguchi、Kengo Oka、Tomoaki Matsumoto、Hiroyoshi Kanai、Kazunori Utani、Seiichiro Imamura
Applied Catalysis A: General 301(1) 66-74 2006年2月 [査読有り]