Structural Lattice Distortion Research Articles

Synthesis and thermoelectric properties of thermoelectric materials of the skutterudites In0.3Co4Sb12-xSex

Thermoelectric materials of the skutterudites In0.3Co4Sb12-xSex(x=0—0.3) were prepared by melt-annealing and spark plasma sintering. The existence forms of the element In were investigated, and the effect of doping Se in In filled-skutterudites on the structure and thermoelectric properties were also studied systematically. The element In could be filled into the hole structure of skutterudite, and the excessive In exists as InSb in the boundary of grains. After the substitution of Se for Sb, the lattice parameters decrease, and the filling fraction limit of In decreases. All the compounds of In0.3Co4Sb12-xSex(x=0—0.3) show n-type conduction. With the Se doping amount increasing, the carrier concentration and electrical conductivity decrease, and the Seebeck coefficient increases, and the power factor decreases slightly. Since the introduction of Se substitution brings about quality fluctuation and lattice distortion in structure, moderate amount of Se substitution can lower the thermal conductivity largely. The maximum ZT values of both In0.3Co4Sb12 and In0.3Co4Sb11.95Se0.05 samples reach above 1.0.

Magnetoelectricity in the ferrimagnetic Cu2OSeO3: symmetry analysis and Raman scattering study

sublattices ferrimagnet Cu2OSeO3 with a cubic symmetry and a linear magnetoelectric effect. There is no spectroscopic evidence for structural lattice distortions below TC=60K, which are expected due to magnetoelectric coupling. Using symmetry arguments we explain this observation by considering a special type of ferrimagnetic ground state which does not generate a spontaneous electric polarization. Interestingly, Raman scattering shows a strong increase of electric polarization of media through a dynamic magnetoelectric effect as a remarkable enhancement of the scattering intensity below TC. New lines of purely magnetic origin have been detected in the magnetically ordered state. A part of them are attributed as scattering on exchange magnons. Using this observation and further symmetry considerations we argue for strong Dzyaloshinskii–Moriya interaction existing in the Cu2OSeO3.

Muon-spin-relaxation studies of magnetic order and superfluid density in antiferromagnetic NdFeAsO,BaFe2As2, and superconductingBa1−xKxFe2As2

Recently, high-transition-temperature (high-T(c)) superconductivity was discovered in the iron pnictide RFeAsO(1-x)F(x) (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO(1-x)F(x) as the system is tuned from a semimetal to a high-T(c) superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x D 0 : 10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x > 0.06, resulting in an electronic phase diagram remarkably similar to that of the high-T(c) copper oxides. Comparison of the structural evolution of CeFeAsO(1-x)F(x) with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-T(c) superconductivity in these Fe pnictides.

Structural and magnetic phase diagram of CeFeAsO1− xFx and its relation to high-temperature superconductivity

Recently, high-transition-temperature (high-Tc) superconductivity was discovered in the iron pnictide RFeAsO(1-x)F(x) (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO(1-x)F(x) as the system is tuned from a semimetal to a high-Tc superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x=0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x>0.06, resulting in an electronic phase diagram remarkably similar to that of the high-Tc copper oxides. Comparison of the structural evolution of CeFeAsO(1-x)F(x) with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-Tc superconductivity in these Fe pnictides.

Low Energy Spin Waves and Magnetic Interactions inSrFe2As2

We report inelastic neutron scattering studies of magnetic excitations in antiferromagnetically ordered SrFe2As2 (T_{N}=200-220 K), the parent compound of the FeAs-based superconductors. At low temperatures (T=7 K), the magnetic spectrum S(Q,Planck's omega) consists of a Bragg peak at the elastic position (Planck's omega=0 meV), a spin gap (Delta< or =6.5 meV), and sharp spin-wave excitations at higher energies. Based on the observed dispersion relation, we estimate the effective magnetic exchange coupling using a Heisenberg model. On warming across T_{N}, the low-temperature spin gap rapidly closes, with weak critical scattering and spin-spin correlations in the paramagnetic state. The antiferromagnetic order in SrFe2As2 is therefore consistent with a first order phase transition, similar to the structural lattice distortion.