Downloaded by 80.82.77.83 on April 19, 2018 | https://pubs.acs.org Publication Date: January 1, 1963 | doi: 10.1021/ba-1964-0039.pr001
PREFACE
j h e stubborn opposition of Proust to Berthollet's contention that compounds could be of variable composition led to the acceptance of the law of constant composition by the end of the eighteenth century. The law was securely established by the superb analytical work of Stas more than a century ago. This was a necessary step in the approach to nonstoichiometry. The application of the phase rule to the study of systems in equilibrium showed that, in many binary systems, solid phases could have variable composition. Thus about a century later Berthollet's suspicions were seen to have some foundation. The advent of x-ray techniques for the study of crystalline solids contributed greatly to the construction of more detailed phase diagrams in the solidus region, revealing many more i n stances of nonstoichiometry. W i t h i n the last 30 years there has developed a lively interest i n the electronic properties of solids, many of w h i c h depend upon the existence of lattice defects and departures from stoichiometry. T h e deviation from ideal composition i n many cases was found to be well beyond the limits detectable by chemical analysis, while i n other instances broad regions of homogeneity were recorded. W i t h i n recent years, the development of more refined x-ray techniques, combined w i t h artful methods of annealing and of growing single crystals, has recealed that some hitherto board regions of homogeneity can be subdivided into rather sharply defined phases of essentially constant composition. It seemed an appropriate time to call a conference. The symposia of the Division of Inorganic Chemistry of the American C h e m i cal Society have usually been opened by a general lecture on the first day of the meeting, followed i n subsequent sessions by more specific papers. T h e collection of papers presented in this volume includes the general lecture presented by J . S. Anderson. Because solid state chemists tend to become specialized i n their interests, the symposium was arranged under the headings of oxides, hydrides, chalcogenides, and bronzes, although not all of the papers fall into these categories. A l l of the papers were by invitation, but in each of the divisions, one author was asked to give a general survey of the problem of nonstoichiometry. These were given by the following speakers: A . D . Wadsley on oxides, G . G . L i b o w i t z on hydrides, J . S. Prener on chalcogenides, and M . J . Sienko on bronzes. It is a pleasure to acknowledge the help given me by T . R . P. G i b b of Tufts University and E p h r a i m Banks of the Polytechnic Institute of Brooklyn i n arranging this symposium. ROLAND WARD
The University of Connecticut Storrs, Conn.
vii Ward; Nonstoichiometric Compounds Advances in Chemistry; American Chemical Society: Washington, DC, 1963.
