"Takehiro Koike,Hena Das,Kengo Oka,Yoshihiro Kusano,Fernando Cubillas,Francisco B.  Bojorqez,Victor Emmanuel  Alvarez-Montano,Shigekazu Ito,Kei Shigematsu,Hayato  Togano,Ikuya Yamada,Hiroki Ishibashi,Kubota Yoshiki,Shigeo Mori,Noboru  Kimizuka,Masaki Azuma","Pressure-Induced YbFe2O4-Type to Spinel Structural Change of InGaMgO4",,"Solids",,"vol. 5","no. 3","pp. 422-433",2024,Aug.
"東 正樹,岡 研吾,山本 孟,酒井 雄樹","相転移型巨大負熱膨張物質",,"応用物理",,"Vol. 88","No. 3",,2019,Mar.
"Takahiro Ogata,Kengo Oka,Masaki Azuma","Negative thermal expansion in electron doped PbVO<sub>3</sub><sub>ー</sub><sub>x</sub>F<sub>x</sub>",,"Applied Physics Express",,"Vol. 12","No. 2","pp. 023005",2019,Jan.
"Hajime Hojo,Kengo Oka,Keisuke Shimizu,Hajime Yamamoto,Ryo Kawabe,Masak Azuma","Development of Bismuth Ferrite as a Piezoelectric and Multiferroic Material by Cobalt Substitution",,"ADVANCED MATERIALS",,"Vol. 30","No. 33","p. 1705665",2018,Aug.
"Takumi Nishikubo,Yuki Sakai,Kengo Oka,Masaichiro Mizumaki,Tetsu Watanuki,Akihiko Machida,Naoyuki Maejima,Shigenori Ueda,Takashi Mizokawa,Masaki Azuma","Optimized negative thermal expansion induced by gradual intermetallic charge transfer in Bi<sub>1</sub><sub>-</sub><sub>x</sub>Sb<sub>x</sub>NiO<sub>3</sub>",,"Applied physics express",,"Vol. 11","No. 6","p. 061102",2018,June
"M. Azuma,Y. Sakai,T. Nishikubo,M. Mizumaki,T. Watanuki,T. Mizokawa,K. Oka,H. Hojo,M. Naka","Systematic charge distribution changes in Bi- and Pb-3d transition metal perovskites",,"Dalton Transactions",,"Vol. 47","No. 5","p. 1371-1377",2018,Feb.
"K.Oka,T.Yamauchi,S.Kanungo,T.Shimazu,K.Ohishi,Y. Uwatoko,M.Azuma,T.Saha-Dasgupta","Experimental and Theoretical Studies of the Metallic Conductivity in Cubic PbVO<sub>3</sub> under High Pressure",,"JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN",,"Vol. 87","No. 2","p. 024801",2018,Feb.
"Y. Okimoto,S. Naruse,R. Fukaya,T. Ishikawa,S. Koshihara,K. Oka,M. Azuma,K. Tanaka,H. Hirori","Ultrafast Control of the Polarity of BiCoO<sub>3</sub> by Orbital Excitation as Investigated by Femtosecond Spectroscopy",,"Physical Review Applied",,"Vol. 7","No. 6","p. 064016",2017,June
"Yuki Sakai,Junye Yang,Runze Yu,Hajime Hojo,Ikuya Yamada,Ping Miao,Sanghyun Lee,Shuki Torii,Takashi Kamiyama,Marjana Le?ai?,G.Bihlmayer,M. Mizumaki,J.Komiyama,T.Mizokawa,H.Yamamoto,T.Nishikubo,Y.Hattori,K. Oka,Y.Yin,J.Dai,W.Li,S.Ueda,A.Aimi,D.Mori,Y. Inaguma,Z.Hu,T. Uozumi,C.Jin,Y.Long,Masaki Azuma","A-site and B-site charge orderings in an s-d level controlled perovskite oxide PbCoO<sub>3</sub>",,"Journal of the American Chemical Society",,"Vol. 139","No. 12","pp. 4574-4581",2017,Mar.
"Mirza HK Rubel,Takahiro  Takei,Nobuhiro Kumada,M Mozahar Ali,Akira  Miura,Kiyoharu Tadanaga,Kengo Oka,Masaki Azuma,Eisuke Magome,Chikako Moriyoshi","Hydrothermal Synthesis, Structure, and Superconductivity of Simple Cubic Perovskite (Ba<sub>0. 62</sub>K<sub>0. 38</sub>)(Bi<sub>0. 92</sub>Mg<sub>0. 08</sub>) O<sub>3</sub> with T<sub> c</sub>? 30 K",,"Inorganic Chemistry",,,,,2017,Feb.
"Nakano Kiho,Oka Kengo,Watanuki Tetsu,Mizumaki Masaichiro,Machida  Akihiko,Agui Akane,Kim  Hyunjeong,Komiyama Jun,Mizokawa Takashi,Nishikubo Takumi,Masaki Azuma","Glassy Distribution of Bi3+/Bi5+ in Bi1?x Pb x NiO3 and Negative Thermal Expansion Induced by Intermetallic Charge Transfer",,"Chemistry of Materials",,"Vol. 28","No. 17","pp. 6062-6067",2016,Aug.
"Kengo Oka,Hajime Hojo,Masaki Azuma,Katsuyoshi Oh-ishi","Temperature-Independent, Large Dielectric Constant Induced by Vacancy and Partial Anion Order in the Oxyfluoride Pyrochlore Pb<sub>2</sub>Ti<sub>2</sub>O<sub>6</sub>− <sub>δ</sub>F<sub>2</sub><sub>δ</sub>",,"Chemistry of Materials",,"Vol. 28","No. 15","pp. 5554-5559",2016,July
"Octavianti Naa,Nobuhiro Kumada,Akira Miura,Takahiro Takei,Masaki Azuma,Yoshihiro Kusano,Kengo Oka","High-Pressure Polymorph of NaBiO<sub>3</sub>",,"Inorganic Chemistry",,"Vol. 55","No. 12","pp. 5747-5749",2016,June
"Naa Octavianti,Nobuhiro Kumada,Miura  Akira,Takahiro Takei,Masaki Azuma,Yoshihiro Kusano,Kengo Oka","High-Pressure Polymorph of NaBiO3",,"Inorganic chemistry",,"Vol. 55","No. 12","pp. 5747-5749",2016,June
"Runze Yu,Narumi Matsuda,Ken Tominaga,Keisuke Shimizu,Hajime Hojo,Yuki Sakai,Hajime Yamamoto,Kengo Oka,Masaki Azuma","High-Temperature Monoclinic Cc Phase with Reduced c/a Ratio in Bi-based Perovskite Compound Bi<sub>2</sub>ZnTi<sub>1</sub>−<sub>x</sub>Mn<sub>x</sub>O<sub>6</sub>",,"Inorganic Chemistry",,"Vol. 55","No. 12","pp. 6124-6129",2016,June
"Hajime Yamamoto,Takumi Kihara,Kengo Oka,Tokunaga Masashi,Ko Mibu,Masaki Azuma","Spin Structure Change in Co-Substituted BiFeO<sub>3 </sub>",,"Journal of the Physical Society of Japan",,"Vol. 85",,"pp. 064704-1-4",2016,May
"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 Avdeev","Hydrothermal Synthesis, Crystal Structure, and Superconductivity of a Double-Perovskite Bi Oxide",,"Chem Mater",,"Vol. 28",,"pp. 459-465",2016,
"Masaki Azuma,Kengo Oka,Koichiro Nabetani","Negative thermal expansion induced by intermetallic charge transfer",,"Science and Technology of Advanced Materials",,"Vol. 16",,"pp. 034904 1-8",2015,Sept.
"Runze Yu,Hajime Hojo,Tetsu Watanuki,Masaichiro Mizumaki,Takashi Mizokawa,Kengo Oka,Hyunjeong  Kim,Akihiko Machida,Kouji Sakaki,Yumiko Nakamura,Aguin Akane,Daisuke Mori,Yoshiyuki Inaguma,Martin Schlipf,Konstantin  Z. Rushchanskii,Marjana Lezaic,Masaaki Matsuda,Jie Ma,Stuart Calder,Masahiko Isobe,Yuichi Ikuhara,Masaki Azuma","Melting of Pb Charge Glass and Simultaneous Pb−Cr Charge Transfer in PbCrO<sub>3 </sub> as the Origin of Volume Collapse",,"Journal of the American Chemical Society",,"Vol. 137",,"pp. 12719-12728",2015,Sept.
"松田奈瑠美,于 潤澤,北條 元,東 正樹,岡研吾","適度な c/a 比を持つ単斜晶 ヘ?ロフ?スカイトBi<sub>2</sub>ZnTi<sub>1-x</sub>Mn<sub>x</sub>O<sub>6</sub>","強誘電体応用会議",,,,,,2015,May
"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","Hydrothermal synthesis of a new  Bi-based (Ba<sub>0.82</sub>K<sub>0.18</sub>)(Bi<sub>0.53</sub>Pb<sub>0.47</sub>)O<sub>3</sub> superconductor",,"Journal of Alloys and Compounds",,"Vol. 634",,"pp. 208?214",2015,
"K. Nabetani,Y. Muramatsu,K. Oka,Kiho Nakano,H. Hojo,M. Mizumaki,A. Agui,Y.  Higo,N. Hayashi,M. Takano,M. Azuma","Suppression of temperature hysteresis in negative thermal expansion compound BiNi1− x Fe x O3 and zero-thermal expansion composite",,"APPLIED PHYSICS LETTERS",,"Vol. 106",,"pp. 061912",2015,
"N. Ishimatsu,T. Watanabe,K. Oka,M. Azuma,M. Mizumaki,K. Nitta,T. Ina,N. Kawamura","Differences in local structure around Co and Fe of the BiCo<sub>1</sub>−<sub>x</sub> Fe<sub>x</sub> O<sub>3</sub> system determined by x-ray absorption fine structure",,"PHYSICAL REVIEW B",,"Vol. 92",,"pp. 054108-1-9",2015,
"Sunseng Pyon,Kazutaka Kudo,Jun-ichi Matsumura,Hiroyuki Ishii,Genta Matsuo,Nohara Minoru,Hojo Hajime,Oka Kengo,Azuma Masaki,Garlea. V.  Ovidiu","Superconductivity in Noncentrosymmetric Iridium Silicide Li2IrSi3",,"JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN",,"Vol. 83","No. 9","pp. 093706",2014,Sept.
"Kousuke Nishimura,Ikuya Yamada,Kengo Oka,Yuichi Shimakawa,Masaki Azuma","High-pressure synthesis of BaVO3: A new cubic perovskite",,"JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS",,"Vol. 75","No. 6","pp. 710-712",2014,June
"Rubel Mirza H. K,Miura Akira,Takei Takahiro,Kumada Nobuhiro,Ali M. Mozahar,Nagao Masanori,Watauchi Satoshi,Tanaka Isao,Oka Kengo,Azuma Masaki,Magome Eisuke,Moriyoshi Chikako,Kuroiwa Yoshihiro,Islam A. K. M. Azharul","Superconducting Double Perovskite Bismuth Oxide Prepared by a Low-Temperature Hydrothermal Reaction",,"ANGEWANDTE CHEMIE-INTERNATIONAL EDITION",,"Vol. 53","No. 14","pp. 3599-3603",2014,Apr.
"奈部谷 光一郎,岡 研吾,東 正樹","BiNi<sub>1</sub>−<sub>x</sub>Fe<sub>x</sub>O<sub>3 </sub>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",,"粉体および粉末冶金",,"Vol. 61","No. 1","pp. 35-37",2014,Jan.
"村松 裕也,奈部谷 光一郎,岡 研吾,東 正樹","巨大な負の熱膨張を示すペロブスカイトBiNiO<sub>3</sub> を用いたゼロ熱膨張コンポジットの作製",,"粉体および粉末冶金",,"Vol. 61","No. 1","pp. 39-43",2014,Jan.
"Romain  Gautier,Kengo Oka,Takumi Kihara,Nitesh Kumar,Athinarayanan Sundaresan,M  Tokunaga,Masaki Azuma,Kenneth R. Poeppelmeier","Spin Frustration from cis-Edge or -Corner Sharing Metal-Centered Octahedra",,"Journal of the american chemical society",,"Vol. 135",,"pp. 19268-19274",2013,Dec.
"Izabela Sosnowska,Masaki Azuma,Rados?aw Przenios?o,Dariusz Wardecki,Wei-tin Chen,Kengo Oka,Yuichi Shimakawa","Crystal and Magnetic Structure in Co-Substituted BiFeO<sub>3</sub>",,"Inorganic Chemistry",,"Vol. 52",,"pp. 13269-13277",2013,Nov.
"岡 研吾,東 正樹,森 茂生","BiCo<sub>1</sub>?<sub>x</sub>Fe<sub>x</sub>O<sub>3</sub> の分極回転現象",,"日本結晶学会誌",,"Vol. 55","No. 5","pp. 278-284",2013,Oct.
"Ikuya YAMADA,Kentaro  SHIRO,Kengo OKA,Masaki AZUMA,Tetsuo IRIFUNE","Direct observation of negative thermal expansion in SrCu?Fe?O??",,"Journal of the Ceramic Society of Japan",,"Vol. 121","No. 1418","pp. 912-914",2013,Oct.
"Makoto Kubota,Kengo Oka,Hisato Yabuta,Kaoru Miura,Masaki Azuma","Structure and Magnetic Properties of BiFe<sub>1</sub>−<sub>x</sub>Co<sub>x</sub>O<sub>3 </sub>andBi<sub>0.9</sub>Sm<sub>0.1</sub>Fe<sub>1</sub>−<sub>x</sub>Co<sub>x</sub>O<sub>3</sub>",,"Inorganic Chemistry",,"Vol. 52",,"pp. 10698-10704",2013,Sept.
"Kengo Oka,Koichiro Nabetani,Chika Sakaguchi,Hayato Seki,Michel  Czapski,Yuichi Shimakawa,Masaki Azuma","Tuning negative thermal expansion in Bi<sub>1</sub>-<sub>X</sub>Ln<sub>X</sub>NiO<sub>3</sub>(Ln=La,Nd,Eu,Dy)",,"APPLIED PHYSICS LETTERS",,"Vol. 103",,"pp. 061909-1-3",2013,Aug.
"Kengo Oka,Masaichiro Mizumaki,Chika Sakaguchi,Alexandra  Sinclair,Clemens  Ritter,J. Paul Attfield,Masaki Azuma","Intermetallic charge-transfer transition in Bi<sub>1</sub>−<sub>x</sub>La<sub>x</sub>NiO<sub>3</sub> as the origin of the colossal negative thermal expansion",,"PHYSICAL REVIEW B",,"Vol. 88",,,2013,July
"東 正樹,岡 研吾","ぺロブスカイトBiNiO?におけるサイト間電荷移動と巨大負の熱膨張",,"日本結晶学会誌",,"Vol. 54","No. 6","pp. 325-331",2012,Dec.
"Kengo Oka,Tsukasa koyama,Tomoatsu Ozaki,Yuichi Shimakawa,Masaki Azuma,Shigeo Mori","Polarization Rotation in the Monoclinic  Perovskite  BiCo1_xFex03",,"Angewandte Chemie-International Edition",,"Vol. 51","No. 32","pp. 7977-7980",2012,Aug.
"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","Sm置換BiFeO?の相転移挙動",,"粉体および粉末冶金",,"Vol. 59","No. 5","pp. 239-245",2012,May
"N. Onishi,K. Oka,M. Azuma,Y. Shimakawa,Yukitoshi Motome,Toshifumi Taniguchi,M. Hiraishi,M. Miyazaki,Tetsuya Masuda,A. Koda,R. Kadono,Kenji Kojima","Magnetic ground state of the frustrated honeycomb lattice antiferromagnet Bi3Mn4O12(NO3)",,"PHYSICAL REVIEW B",,"Vol. 85",,"pp. 184412 1-6",2012,May
"Yoshihiro Tsujimoto,Clastin I.  Sathish,Kun-Pyo Hong,Kengo Oka,Masaki Azuma,Yanfeng  Guo,Yoshitaka Matsushita,Kazunari Yamaura,Eiji Takayama-Muromachi","Crystal Structural, Magnetic, and Transport Properties of Layered Cobalt Oxyfluorides, Sr2CoO3+xF1−x (0 ? x ? 0.15)",,"Inorganic Chemistry",,"Vol. 51",,"pp. 4802−4809",2012,Apr.
"Makoto Kubota,Kengo Oka,Yoshitaka Nakamura,Hisato Yabuta,Kaoru Miura,Yuichi Shimakawa,Masaki Azuma","Sequential Phase Transitions in Sm Substituted BiFeO3",,"Jpn. J. Appl. Phys.",,"Vol. 50","No. 9","pp. 09NE08",2011,Sept.
"Watanabe Takayuki,Mikio Shimada,Toshiaki Aiba,Hisato Yabuta,Kaoru Miura,Kengo Oka,Masaki Azuma,Satoshi Wada,Nobuhiro Kumada","Structural Transformation of Hexagonal (0001)BaTiO3 Ceramics to Tetragonal (111)BaTiO3 Ceramics",,"JAPANESE JOURNAL OF APPLIED PHYSICS",,"Vol. 50","No. 9","pp. 09ND01-1-4",2011,Sept.
"Sudayama, T,Y. Wakisaka,H.  Wadati,Mizokawa,G. A. Sawatzky,D.G. Hawthorn,T. Z. Regier,Kengo Oka,Masaki Azuma,M. Shimakawa, Y","Co-O-O-Co superexchange pathways enhanced by small charge-transfer energy in multiferroic BiCoO(3)",,"Pysical Review B",,"Vol. 83",,"pp. 235105-1-5",2011,June
"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","Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer",,"NATURE COMMUNICATIONS",,"Vol. 2","No. 347","pp. 1-5",2011,June
"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","Pressure-Induced Spin-State Transition in BiCoO3",,"JOURNAL OF THE AMERICAN CHEMICAL SOCIETY",,"Vol. 132","No. 27","p. 9438",2010,July
"Kengo Oka,Masaki Azuma,Alexei A. Belik,Hiroshi Kojitani,Masaki Akaogi,Mikio Takano,Yuichi Shimakawa","Pressure-Induced Transformation of 6H Hexagonal to 3C Perovskite Structure in PbMnO3",,"Inorganic Chemistry",,"Vol. 48","No. 5","pp. 2285",2009,Mar.
"Long, Y.W.,T. Saito,T. Tohyama,K. Oka,M. Azuma,Y. Shimakawa","Intermetallic Charge Transfer in A-Site-Ordered Double Perovskite BiCu3Fe4O12.",,"Inog. Chem.",,"Vol. 48",,"pp. 8489-8492",2009,
"Kohki Satoh,Masatoshi Hiraishi,Masanori Miyazaki,Satoshi Takeshita,Akihiro Koda,R. Kadono,I. Yamada,K. Oka,M. Azuma,Y. Shimakawa,M. Takano","Effect of Zn substitution for Cu on Ca2-xNaxCuO2Cl2 near the hole concentration of 1/8 per Cu.",,"Physica B-Condensed Matter",,"Vol. 404",,"pp. 713-716",2009,
"H. Jiang,N. Kumada,Y. Yonesaki,T. Takei,N. Kinomura,M. Yashima,M. Azuma,K. Oka,Y. Shimakawa","Hydrothermal Synthesis of a New Double Perovskite-Type Bismuthate, (Ba0.75K0.14H0.11)BiO3?nH2O",,"Jpn. J. Appl. Phys.",,"Vol. 48",,"pp. 010216-1-3",2009,
"Kengo Oka,Masaki Azuma,Ikuya Yamada,Soshi Takeshita,Kohki Satoh,Akihiro Koda,Ryosuke Kadono,Mikio Takano,Yuichi Shimakawa","Magnetic ground-state of perovskite PbVO3 with large tetragonal distortion",,"Inorganic Chemistry",,"Vol. 47","No. 16","pp. 7355",2008,Aug.
"Kengo Oka,Masaki Azuma,Naoaki Hayashi,Shigetoshi Muranaka,Yasuo Narumi,Koichi Kindo,Masatsune Kato,Yoji Koike,Yuichi Shimakawa,Mikio Takano","Charge and magnetic orderings in the triangular-lattice antiferromagnet InFe2O4",,"Journal of the Physical Society of Japan",,"Vol. 77","No. 6","pp. 064803",2008,June
"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","三角格子反強磁性体InFe2O4の合成と物性",,"粉体および粉末冶金",,"Vol. 54","No. 1","pp. 53-57",2007,
"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,Alexei Belik","Bi, Pb-3d遷移金属ペロブスカイトの構造物性研究",,"日本結晶学会誌",,"Vol. 49","No. 6","pp. 335-340",2007,
"Kengo Oka,Siichiro Imamura","Active state of tungsten oxides on WO3/ZrO2 catalyst for steam reforming of dimethyl ether combined with CuO/CeO2",,"Applied Catalysis A-General",,"Vol. 309","No. 2","pp. 187",2006,Aug.