CATION NONSTOICHIOMETRY IN TIN-MONOXIDE-PHASE SN1-DELTA-O WITH TWEED MICROSTRUCTURE

We report a chemical, thermogravimetric, and electron-diffraction/micr oscopy study of a tin-monoxide phase. A large deviation from the ideal stoichiometry is observed due to metal vacancies, resulting in the fo rmula Sn1-deltaO. This nonstoichiometry is an intrinsic feature of thi s material and is accommodated through the formation of static transve rse displacive modulations along the (hh0) directions. giving a tweed microstructure without the introduction of complex arrangements of vac ancy interstitials (as in wustite). Our observation constitutes a diff erent way of accommodating large deviations from ideal stoichiometries , especially in comparison with the will-known behavior of the transit ion-metal monoxides with the NaCl-type structure. The difference arise s most likely from the layerlike nature of the alpha-PbO (B-10) struct ural type with average tetragonal symmetry and P4/nmm space group. Met al vacancies cause a strain coupling which stabilizes the highly disor dered nonstoichiometric phase. Dynamical instabilities were not observ ed. An origin for the thermal instability of the material is suggested . A comparison with PbO, the only isostructural compound, is outlined. SnO is shown to be a beam-sensitive material.