Divalent chromium in the octahedral positions of the novel hybrid perovskites CH3NH3Pb1-xCrx(Br,Cl)3 (x ¼ 0.25, 0.5): induction of narrow bands inside the bandgap - Serrano-Sánchez, F.; Conesa, J. C.; Rodrigues, João Elias Figueiredo Soares; Marini, C.; Martínez, José L.; Alonso, José A. (Journal of Alloys and Compounds, 2020)