"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