Neutron diffraction studies on the thermal expansion and anomalous mechanics in the perovskite-type [C(ND2)3]Me2+(DCOO)3 [Me = Cu, Mn, Co]

Abstract

The thermomechanical characteristics of [C(ND₂)₃]Me²⁺(DCOO)₃ [Me = Cu, Co, Mn] have been evaluated by single-crystal and powder neutron diffraction. [C(ND₂)₃]Cu²⁺(DCOO)₃, presenting with the polar space group Pna2₁, exhibits lattice expansion along the a and c axes, while the b-axis shows a crossover from negative to positive thermal expansion. The relative change in lattice parameters is independent in all directions, resulting in anisotropic thermal characteristics. The thermomechanical response is a collective effect of hingeing and deformation, with the former as the dominant factor. In this study, every individual hinge and strut are evaluated, unlike the conventional averaging of the mechanical units. The Mn cousin displays a higher magnitude of octahedral tilting than the Co-twin. Such an effect has direct consequences on higher expansivity for manganese guanidinium formate along all directions. Hingeing is the dominant factor in both Mn and Co-twins, with their relative values much closer than reported earlier.