ABSTRACT
Hybrid layered double perovskite (HLDP) halides comprise hexacoordinated 1+ and 3+ metals in the octahedral sites within a perovskite layer and organic amine cations between the layers. Progress on such materials has hitherto been limited to compounds containing main group 3+ ions isoelectronic with PbII (such as SbIII and BiIII). Here, we report eight HLDP halides from the A2MIMIIIX8 family, where A = para-phenylenediammonium (PPDA), 1,4-butanediammonium (1,4-BDA), or 1,3-propanediammonium (1,3-PDA); MI = Cu or Ag; MIII = Ru or Mo; X = Cl or Br. The optical band gaps, which lie in the range 1.55 to 2.05 eV, are tunable according to the layer composition, but are largely independent of the spacer. Magnetic measurements carried out for (PPDA)2AgIRuIIICl8 and (PPDA)2AgIMoIIICl8 show no obvious evidence of a magnetic ordering transition. While the t2g3 MoIII compound displays Curie-Weiss behavior for a spin-only d3 ion, the t2g5 RuIII compound displays marked deviations from the Kotani theory.
ABSTRACT
Vacancy-ordered double perovskites are attracting significant attention due to their chemical diversity and interesting optoelectronic properties. With a view to understanding both the optical and magnetic properties of these compounds, two series of RuIV halides are presented; A2 RuCl6 and A2 RuBr6 , where A is K, NH4 , Rb or Cs. We show that the optical properties and spin-orbit coupling (SOC) behavior can be tuned through changing the A cation and the halide. Within a series, the energy of the ligand-to-metal charge transfer increases as the unit cell expands with the larger A cation, and the band gaps are higher for the respective chlorides than for the bromides. The magnetic moments of the systems are temperature dependent due to a non-magnetic ground state with Jeff =0 caused by SOC. Ru-X covalency, and consequently, the delocalization of metal d-electrons, result in systematic trends of the SOC constants due to variations in the A cation and the halide anion.
ABSTRACT
There has been a great deal of recent interest in extended compounds containing Ru3+ and Ru4+ in light of their range of unusual physical properties. Many of these properties are displayed in compounds with the perovskite and related structures. Here we report an array of structurally diverse hybrid ruthenium halide perovskites and related compounds: MA2 RuX6 (X=Cl or Br), MA2 MRuX6 (M=Na, K or Ag; X=Cl or Br) and MA3 Ru2 X9 (X=Br) based upon the use of methylammonium (MA=CH3 NH3 + ) on the perovskite A site. The compounds MA2 RuX6 with Ru4+ crystallize in the trigonal space group R 3 â¾ m and can be described as vacancy-ordered double-perovskites. The ordered compounds MA2 MRuX6 with M+ and Ru3+ crystallize in a structure related to BaNiO3 with alternating MX6 and RuX6 face-shared octahedra forming linear chains in the trigonal P 3 â¾ m space group. The compound MA3 Ru2 Br9 crystallizes in the orthorhombic Cmcm space group and displays pairs of face-sharing octahedra forming isolated Ru2 Br9 moieties with very short Ru-Ru contacts of 2.789â Å. The structural details, including the role of hydrogen bonding and dimensionality, as well as the optical and magnetic properties of these compounds are described. The magnetic behavior of all three classes of compounds is influenced by spin-orbit coupling and their temperature-dependent behavior has been compared with the predictions of the appropriate Kotani models.
ABSTRACT
Recently discovered alongside its sister compounds KV_{3}Sb_{5} and RbV_{3}Sb_{5}, CsV_{3}Sb_{5} crystallizes with an ideal kagome network of vanadium and antimonene layers separated by alkali metal ions. This work presents the electronic properties of CsV_{3}Sb_{5}, demonstrating bulk superconductivity in single crystals with a T_{c}=2.5 K. The normal state electronic structure is studied via angle-resolved photoemission spectroscopy and density-functional theory, which categorize CsV_{3}Sb_{5} as a Z_{2} topological metal. Multiple protected Dirac crossings are predicted in close proximity to the Fermi level (E_{F}), and signatures of normal state correlation effects are also suggested by a high-temperature charge density wavelike instability. The implications for the formation of unconventional superconductivity in this material are discussed.
