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Study of conditions of crystallization and of thermodynamic properties of selected intermetallic compounds of lanthanides
Štěpánová, Karla ; Svoboda, Pavel (advisor) ; Javorský, Pavel (referee)
In this diploma work, I present the results of structural and thermodynamic studies of selected RNi4Si (R - La, Pr, Nd, Sm, Gd, Er, Ho, Dy) compounds. Contrary to its parent compound RNi5, these compounds do not crystallize in the hexagonal structure (CaCu5-type, space group P6/mmm). Instead of this, the orthorhombic structure with the space group Cmmm was found. The phase transition temperatures were determined from the zero-field specific heat measurement. Apart of PrNi4Si all compounds order ferromagnetically below the transition temperature. The phase transition temperature dependence of these compounds is in very good agreement with the de Gennes factor. Specific heat was analysed using a sum of the electronic, phonon and magnetic contribution. The significant magnetic contribution was fully described by the Schottky formula for n-level system. The magnetic entropy was calculated and is approaching the expected free ion entropy. Specific heat measurement of NdNi4Si compound showed structure transition at higher temperatures. Anisotropic properties cannot be studied on a polycrystalline sample and further studies must be carried out on the single-crystal. Trials to prepare single-crystals confirmed an incongruency of these samples. The mozaicity of measured samples is very high having the hexagonal...
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