Analysis of low temperature specific heat in the ferromagnetic state of the Ca-doped manganites

X-ray diffraction and Raman data on the pressure induced phase transitions of a nanometric zirconia, ZrO₂, are analyzed via a classical phenomenological Landau approach of the bulk. It is concluded that the initial tetragonal structure (D _4h ¹⁵), which is a metastable bulk state of zirconia at ambient conditions, evolves continuously towards the ideal cubic fluorite structure (O _h ⁵) via an intermediate tetragonal form (D _4h ¹⁴). The proposed phenomenological model describes consistently all experimental peculiarities, including the hybridization and softening of the low-frequency Raman active modes along with lattice-parameter anomalies.Received: 29 July 2003, Published online: 15 October 2003PACS: 64.70.Nd Structural transitions in nanoscale materials - 61.50.Ks Crystallographic aspects of phase transformations; pressure effects - 61.10.Nz X-ray diffraction