Uniaxial negative thermal expansion in the [(CH3)2NH2]PbBr3 hybrid perovskite

The [(CH 3 ) 2 NH 2 ]PbBr 3 perovskite exhibits an unusual thermal expansion, and we propose a novel thermomechanical mechanism that differs from the typical “ wine-rack ”. Also, we probed the presence of an H-bond between the DMA cation and the framework.