Chemistry Project Abstract
DESCRIPTION OF MAGNETIC TRANSITION TEMPERATURES IN TERMS OF GEOMETRICAL FACTORS FOR PEROVSKITE MANGANITES
Presenter:
Paul J. Dabrowski, Illinois Mathematics and Science Academy, 1500 West Sullivan Road, Aurora, IL, 60506; anubis@imsa.edu
Mentor:
Dr. Bogdan Dabrowski, Northern Illinois University, Faraday Hall West 202, DeKalb, IL, 60115; 815-753-6474; 815-753-8564; dabrowski@anl.gov
Abstract:
Recently, interest in perovskite oxide materials, which have a chemical formula of ABO3, has peaked after the discovery of their superconductivity and colossal magneto-resistance at high temperatures. The importance of these materials is in that a mixture of A-site cations can produce desired properties in the material. In general, this project has focused on materials where B=Mn and A holds a strong, electronegative cation (such as divalent Ba, Sr, Ca or trivalent La, Pr, Nd). The aim of this work was to develop a database and 3d plotting program that would relate structural to physical characteristics. In particular, the tolerance factor (t), variance in sizes of A-site cations (s), and the phase-transition temperature were taken into consideration. The tolerance factor has frequently been used to describe and predict temperatures at which the material will change from a paramagnetic to ferromagnetic or anti-ferromagnetic state (Tn), and is based on relative size of A and B-site cations (when t = 1, the material has cubic crystal structure). It has been concluded, by analysis of both recently obtained and old data, that a new tolerance factor that takes s into account would be more effective in predicting characteristics of perovskite manganites.