Landau theory for a cubic to tetragonal structural phase transformation

• Published in: Physica B + C Vol. 119; no. 1; p. 56
• Main Authors: Choy, T.C., Young, W., Lowde, R.D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.1983
• ISSN: 0378-4363
• DOI: 10.1016/0378-4363(83)90165-1

We present a new phenomenological description of a cubic to tetragonal martensitic phase transformation. The essential feature of the martensitic transition in which the transition takes a substantial temperature interval to complete is incorporated by starting from a free energy that contains the fractional volume of converted material as an additional order parameter. This model is remarkable in having a co-existing first- and second-order phase transition at the same critical temperature T M. The c-axis order parameter has a jump, while the a-axis and fractional conversion x remain continuous at T M. We have found it necessary to impose a generalised constraint condition related to the internal pressure on the system. We discuss the origin of this constraint and relate it to the magnetoelastic coupling which drives the phase transformation. Application of this theory to experiments on the alloy Mn 85Ni 9C 6 in its antiferromagnetic state ( T M< T N) is discussed.