Influence of microstructure on symmetry determination of piezoceramics. Issue 3 (20th April 2018) - Hinterstein, M.
Abstract : This study shows that with temperature‐dependent high‐resolution X‐ray and neutron diffraction the physical origin of observations cannot be revealed on the basis of agreement factors alone. However, when the diffraction results were combined with additional electron microscopy and electron probe microanalysis, it was possible to confirm that a segregation of substituents results in a complex reflection splitting and phase coexistence that can be misinterpreted as monoclinic symmetry. Abstract : The origin of the complex reflection splitting in potassium sodium niobate doped with lithium and manganese was investigated using temperature‐dependent high‐resolution X‐ray and neutron diffraction as well as electron probe microanalysis and scanning electron microscopy. Two structural models were developed from the diffraction data. A single‐phase monoclinic Pm model is known from the literature and is able to reproduce the diffraction patterns perfectly. However, a model with phase coexistence of two classical orthorhombic Amm 2 phases can also reproduce the diffraction data with equal accuracy. Scanning electron microscopy in combination with electron probe microanalysis revealed segregation of the A ‐site substituents potassium and sodium. This favours the model with phase coexistence and confirms the need for comprehensive analyses with complementary methods to cover a broad range of length scales as well as to assess both average and local structure.