POLYMORPHISM of crystal structures—alternative crystalstructures resulting from variations in ionic and molecularpacking1 and conformation2—is important ina number of fields in solid-state chemistry, includingbiomineralization3 (in the mineral phases of calciumcarbonate3, for example), polymer science(polypropylene4, for example), explosives (ammonium nitrate,lead azide5), nonlinear optical materials6,ceramics and catalysis (zeolites and metal oxides7). In thepharmaceutical and fine-chemicals industries, polymorphism is central to bothproduction process design and product activity8. Here we showthat crystal twinning can stabilize a crystal polymorph that is otherwise notthe most stable form. We use electron microscopy, X-ray diffraction and Ramanspectroscopy to show that the apparently indefinite persistence of a metastablepolymorph of terephthalic acid can be explained on this basis. If twinning canbe engineered, it may therefore provide a means for stabilizing crystal phaseswith useful physical properties.

Abstract The structure of vapour-deposited Fe-Cu alloys was analysed and compared with that obtained by quenching from the liquid and solid state. Transmission electron microscopy was used to observe grain size at room temperature and precipitation at elevated temperatures. A discussion of... mehr

Copyright: Copyright 1978 Chapman and Hall Ltd. mehr

Abstract It is shown that the tetragonal phase can be stabilized in the sintered body of a partially stabilized zirconia (PSZ) containing low concentrations of yttria. Such sintered body containing the metastable phase undergoes stress-induced phase transformation by the absorption of thermal or... mehr

Copyright: Copyright 1977 Chapman and Hall Ltd. mehr

It is known that a metastable crystalline thin-film structure can often be stabilized by choosing a suitable substrate. For single-crystal thin films, this pseudomorphic growth has been attributed to the stabilization of the metastable phase by epitaxial growth. However, in the polycrystalline... mehr