Test Of The Dynamic-Domain And Critical Scattering Hypotheses In Cubic Methylammonium Lead Triiodide

We investigate the hypothesis of dynamic tetragonal domains occurring in cubic CH3NH3PbI3 using high-resolution neutron spectroscopy to study a fully deuterated single crystal. The R-point scattering above the 327.5 K cubic-tetragonal phase transition is always resolution limited in energy and therefore inconsistent with dynamic-domain predictions. This behavior is instead consistent with the central peak phenomenon observed in other perovskites. The scattering may originate from small, static, tetragonalphase domains nucleating about crystal defects, and the temperature dependence demonstrates the transition is first order.