RESUMEN
It is known that as the FeAs4 tetrahedron in the Fe-based superconductor is close to the regular tetrahedron, critical temperature (Tc) can be greatly increased. Recently, a Co-based superconductor of LaCoSi (4 K) with "111" structure was found. In this work, we improve the Tc of LaCoSi through structural regulation. Tc can be increased by the chemical substitution of Co by Fe, while the superconductivity is suppressed by the Ni substitution. The combined analysis of neutron and synchrotron X-ray powder diffractions reveals that the change of the Si-Co-Si bond angles of the CoSi4 tetrahedron is possibly responsible for the determination of superconducting properties. The Fe chemical substitution is favorable for the formation of the regular tetrahedron of CoSi4. The present new Co-based superconductor of LaCoSi provides a possible method to enhance the superconductivity performance of the Co-based superconductors via controlling Co-based tetrahedra similar to those well established in the Fe-based superconductors.
RESUMEN
A 12-layer hexagonal perovskite Ba4SbMn3O12 (space group: R3Ìm; a = 5.72733(3) Å, and c = 28.1770(3) Å) has been synthesized by high-temperature solid-state reactions and studied using powder X-ray and neutron diffraction and magnetization measurements. This 12R polytype structure contains one corner-sharing (Sb, Mn)O6 octahedron and a trimer of face-sharing MnO6 octahedra per formula unit. Ba4SbMn3O12 displays a paramagnetic state of the Mn3 magnetic cluster at 100-200 K, which partially disassociates into individual Mn ions at 250-300 K. The ferromagnetic interaction between these Mn3 clusters is mainly mediated by Mn3+ at the M1 site, leading to dynamic ferromagnetic clusters below T D = â¼70 K and ferromagnetic spin freezing transition at T g = â¼11.5 K. The stability of Mn3 magnetic clusters in the 12R polytypes is related to the intracluster Mn-Mn distance.
RESUMEN
The new hexagonal perovskite phase of composition Ba4Sn1.1Mn2.9O12 has been synthesized by solid-state reactions at 1673 K. The crystal structure has been investigated using X-ray and neutron diffraction. The hexagonal perovskite structure has an ordered arrangement of Sn and Mn ions on the corner-sharing octahedral centers and the face-sharing octahedral centers respectively. Short Mn-Mn distances have been evidenced in the face-sharing trimer of MnO6 octahedra. The magnetic susceptibility shows magnetic cluster behavior, with cluster formation temperature â¼220 K. Antiferromagnetic order has been observed at T N â¼ 6 K. Ba4Sn1.1Mn2.9O12 is a semiconductor with a transport activation energy of 0.61 eV.