Weldemariam, Ashenafi (2007) Mean Field Theory for Structural Phase Transition in Y-Ba-Cu-O. Masters thesis, Addis Ababa University.
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Abstract
The spring-defect-model has been developed earlier for describing the structural phase transition in YBCO (from tetragonal to orthorhombic at ∼900K) in high Tc(. 92K) superconductor is now casted into effective strain-strain interaction Hamiltonian. In this model the connection between elastic distortion and oxygen ordering is described using mean field theory. The lattice static of the Cu-O basal plane is treated in the harmonic approximation in which oxygen and vacancy are modeled via pseudo spin Sˆ = ±1. The strain model is suitable for describing paraelastic (tetragonal) to ferroelastic (orthorhombic) transition in YBCO. The orthorhombic phase is known to be ferroelastic and it develop spontaneous strain due to oxygen ordering in one direction of lattice. We present the results for ferroelastic order parameter, static compliance, frequency dependent compliance and internal friction in terms of all the basic parameter like spring constants K, K0 distortion parameter α, lattice constants a0 of the model. The signature of phase transition is occurred through ferroelastic and anelastic relaxation from mean field approximation of the strain-strain model under the influence of an external in homogeneous stress. These are very important results as far as formation of tweed textures and mechanical behavior in YBCO is concerned. The model is 2D as our focus is on the Cu-O basal plane of 3D structures. Our main aim is to describe the statics and kinetics of the ferroelastic transition in YBCO
| Item Type: | Thesis (Masters) |
|---|---|
| Subjects: | Q Science > Q Science (General) Q Science > QC Physics |
| Divisions: | Africana |
| Depositing User: | Selom Ghislain |
| Date Deposited: | 24 Aug 2018 12:13 |
| Last Modified: | 24 Aug 2018 12:13 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/4892 |
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