Multidimensional Rietveld refinement of high‐pressure neutron diffraction data of PbNCN

High‐pressure neutron powder diffraction data from PbNCN were collected on the high‐pressure diffraction beamline SNAP located at the Spallation Neutron Source (SNS) of Oak Ridge National Laboratory (Tennessee, USA). The diffraction data were analyzed using the novel method of multidimensional (two dimensions for now, potentially more in the future) Rietveld refinement and, for comparison, employing the conventional Rietveld method. To achieve two‐dimensional analysis, a detailed description of the SNAP instrument characteristics was created, serving as an instrument parameter file, and then yielding both cell and spatial parameters as refined under pressure for the first time for solid‐state cyanamides/carbodiimides. The bulk modulus B0 = 25.1 (15) GPa and its derivative B′0 = 11.1 (8) were extracted for PbNCN following the Vinet equation of state. Surprisingly, an internal transition was observed beyond 2.0 (2) GPa, resulting from switching the bond multiplicities (and bending direction) of the NCN2− complex anion. The results were corroborated using electronic structure calculation from first principles, highlighting both local structural and chemical bonding details. The results are presented of a high‐pressure neutron powder diffraction study on lead cyanamide, carried out with the novel method of multidimensional Rietveld refinement. In addition to better resolution than the standard one‐dimensional case, the results show the first evidence of changing C—N bond multiplicities as a function of pressure, numerically quantified from density functional theory calculations.