Numéro
J. Phys. IV France
Volume 03, Numéro C7, Novembre 1993
The 3rd European Conference on Advanced Materials and Processes
Troisiéme Conférence Européenne sur les Matériaux et les Procédés Avancés
Page(s) C7-2047 - C7-2050
DOI http://dx.doi.org/10.1051/jp4:19937327
The 3rd European Conference on Advanced Materials and Processes
Troisiéme Conférence Européenne sur les Matériaux et les Procédés Avancés

J. Phys. IV France 03 (1993) C7-2047-C7-2050

DOI: 10.1051/jp4:19937327

Statistical thermodynamics of ordering systems

L. NOBILI, A. DEL PRETE, U. DUCATI and P.L. CAVALLOTTI

Politecnico di Milano, Dipartimento di Chimica Fisica Applicata, P.zza L. da Vinci 32, 20133 Milano, Italy


Abstract
A statistical thermodynamic approximation for cooperative phenomena in Ising and Heisemberg systems has been developed. Description of order-disorder transformation in alloys as well as evaluation of the magnetic contribution for the free energy of ferromagnets is provided with this approach. The constant coupling approximation is improved by introducing a second pairs reactions after averaging atomic groups, on the analogy of block construction in renormalization group techniques. Temperature variation after renormalizing is taken into account by two suitable temperature functions. As analytic expression for the system free energy is obtained which gives well approximate thermodynamic quantities (order parameter, internal energy, specific heat). In particular, the critical behaviour is properly described, with accurate thermodynamic quantities and right exponents. This approach has been applied to real system, showing what are the differences with ideal Ising system. In order-disorder alloys like β-brass, order parameter and specific heat as a function of temperature are obtained and ordering phenomena are discussed.



© EDP Sciences 1993