Kristallstrukturverfeinerungen an Natriumtrifluorometallaten NaMF3 (M  Mg,Co, Ni,Zn): Oktaederkippung und Toleranzfaktor orthorhombischer Fluorperowskite

Crystal Structure Refinements of Sodium Trifluorometallates NaMF₃ (M ? Mg, Co, Ni, Zn): Tilting of Octahedra and Tolerance Factor of Orthorhombic Fluoroperovskites Based on newly measured X-ray single crystal data the crystal structures of the orthorhombic fluoroperovskites NaMF₃ (M ? Mg, Co, Ni, Zn) were refined in space group Pbnm (GdFeO₃ type, Z = 4). The octahedra are but slightly distorted; the average distances (and bridge angles M? F? M) are: Mg? F = 197.8 pm (150.9°), Co? F = 203.8 pm (146.1°), Ni? F = 200.3 pm (148.0°) and Zn? F = 202.3 pm (147.4°). With respect to the axes of the pseudocell (Z = 1) the octahedra are rotated by tilt angles which vary, including NaMnF₃ and NaFeF₃, between 14.6 and 18.8°. The tilting becomes the more pronounced, the smaller the tolerance factor of the compound, so as to yield uniformly average values of Na? F = 232 pm for the four shortest distances within the [NaF₈] coordination (distorted tetrahedron and bicapped trigonal prism, respectively). Measurements of magnetic powder susceptibilities show that tilting of octahedra is no sufficient cause to produce spin canting resulting in ferromagnetism: This property is confirmed only for NaNiF₃ (T_N = 150 K), whereas NaCoF₃ exhibits a sharp minimum in its χ^?l-T curve (T_N = 75 K) and remains uncanted antiferromagnetic then down to 4.2 K.     

First-principles calculation of the structural,electronic,and magnetic properties of cubic perovskite RbXF_3(X = Mn,V,Co,Fe)

First-principles calculations by means of the full-potential linearized augmented plane wave method using the generalized gradient approximation with correlation effect correction(GGA+U) within the framework of spin polarized density functional theory(DFT+U) are used to study the structural,electronic,and magnetic properties of cubic perovskite compounds RbXF_3(X = Mn,V,Co,and Fe).It is found that the calculated structural parameters,i.e.,lattice constant,bulk modulus,and its pressure derivative are in good agreement with the previous results.Our results reveal that the strong spin polarization of the 3d states of the X atoms is the origin of ferromagnetism in RbXF_3.Cohesive energies and the magnetic moments of RbXF_3 have also been calculated.The calculated electronic properties show the half-metallic nature of RbCoF_3 and RbFeF_3,making these materials suitable for spintronic applications.     

First Principles Investigation of Fluorine Based Strontium Series of Perovskites

Density functional theory is used to explore structural, elastic, and mechanical properties of SrLiF₃, SrNaF₃, SrKF₃ and SrRbF₃ fluoroperovskite compounds by means of an ab-initio Full Potential-Linearized Augmented Plane Wave (FP-LAPW) method. Several lattice parameters are employed to obtain accurate equilibrium volume (V_o). The resultant quantities include ground state energy, elastic constants, shear modulus, bulk modulus, young's modulus, cauchy's pressure, poisson's ratio, shear constant, ratio of elastic anisotropy factor, kleinman's parameter, melting temperature, and lame's coefficient. The calculated structural parameters via DFT as well as analytical methods are found to be consistent with experimental findings. Chemical bonding is used to investigate corresponding chemical trends which authenticate combination of covalent-ionic behavior. Furthermore electron density plots as well as elastic and mechanical properties are reported for the first time which reveals that fluorine based strontium series of perovskites are mechanically stable and posses weak resistance towards shear deformation as compared to resistance towards unidirectional compression while brittleness and ionic behavior is dominated in them which decreases from SrLiF₃ to SrRbF₃. Calculated cauchy's pressure, poisson's ratio and B/G ratio also proves ionic nature in these compounds. The present methodology represents an effective and influential approach to calculate the whole set of elastic and mechanical parameters which would support to understand various physical phenomena and empower device engineers for implementing these materials in numerous applications.