First Principles Study On Phase Stability Of Some Iron Materials

With the rapid development of computer technology and numerical algorithm, the first principle which based on the density functional theory have became the main method of researching the condensed matter performance. Due to the widely used in production and daily life of the ferroelectric materials and ferromagnetic materials, they have become the research hotspots now. The first principle calculation method’s effectiveness has been widely recognized in the study of the ferroelectric materials and ferromagnetic materials properties and phase stability. This paper using the first calculation principle study the phase stability of some iron materials, it includes the magnetic stability of the sp half-metal ferromagnetism SrC and BaC in in rocksalt (RS), zincblende (ZB) and nickel arsenide (NA) structures under external pressure, as well the electronic structure; the structure stability and electronic structure of the ferroelectrics PZT on the Morphotropic Phase Boundary. The study of above materials provide the theory basis and product design for the actual production.Using the first-principles full-potential linearized augmented plane-wave method based on the density functional theory, we investigated the magnetic stability of sp half-metal ferromagnets SrC and BaC in rocksalt (RS), zincblende (ZB) and nickel arsenide (NA) structures under external pressure. The magnetic moments, total energy of magnetic and non-magnetic phases, as well as lattice constants are calculated as a function of pressure. The calculations agree with each other very well and predict the occurrence of the magnetic phase transitions induced by pressure which is resulted from the band widening of anion p states. From our calculation we find that for both SrC and BaC, the rocksalt phase is more stable than the other phases. Moreover, in the same structure, the magnetic stability of SrC is better than that of BaC that indict the stability of magnetism decrease as the atomic number of metal element increase.The energetic stability, structural and electronic properties of rhombohedral and tetragonal PbZr0.5Ti0.5O3are systematically investigated by first-principles plane-wave pseudopotential and virtual crystal approximation (VCA) based on density functional theory, within the framework of local density approximation (LDA) and generalized gradient approximation (GGA). Our calculation results show that the total energy of the rhombohedral phase is lower than that of the tetragonal phase, which suggests that the rhombohedral structure is more energetically stable than the tetragonal one. Furthermore, the structural parameters calculated with the GGA are well consistent with experimental values. From the analysis of electronic structure, we can find the strong hybridization between Ti/Zr d and O2p both in two phases. Furthermore the hybridization between Ti-O is stronger than that between Zr-O; there also exists the hybridization between Pb s, d and O2s,2p. Moreover, the hybridization between Pb5d and O2s in the rhombohedral phase is stronger than that in the tetragonal phase, which indicates that the rhombohedral phase is more stable than the tetragonal phase.