ACuZrQ₃ (A = Rb, Cs; Q = S, Se, Te): Direct Bandgap Semiconductors and Metals with Ultralow Thermal Conductivity

Abstract

ACuZrQ 3 (A = Rb, Cs; Q = S, Se, Te) were synthesized as black platelet crystals. RbCuZrS 3 , RbCuZrSe 3 , and CsCuZrS 3 crystallize in the KCuZrSe 3 structure type with space group Cmcm, and RbCuZrTe 3 and CsCuZrTe 3 crystallize in the lower symmetry space group Pnma. The tellurides exhibit a secondorder Jahn−Teller distortion with off-centering of Zr in its octahedral environment. The magnitude of the distortion is larger in RbCuZrTe 3 than in CsCuZrTe 3 . The structures of β-CsCuS 4 and Rb 2 Cu 5 Te 5 were also determined. CsCuZrS 3 melts at 910 °C and exhibits partial decomposition upon heating at 275 °C, while CsCuZrTe 3 melts incongruently. Our DFT calculations of RbCuZrQ 3 (Q = S, Se) and CsCuZrS 3 indicate direct gap semiconductors in agreement with experiments. ACuZrTe 3 (A = Rb, Cs) were calculated to be metals which was confirmed for RbCuZrTe 3 with variable temperature conductivity measurements and consistent with heat capacity measurements. Spectroscopic measurements found a bandgap and work function of 1.44(5) eV and 4.89(5) eV for RbCuZrS 3 and 0.95(5) eV and 4.67(5) eV for RbCuZrSe 3 , respectively. RbCuZrTe 3 did not exhibit an optical bandgap and has a work function of 4.64(5) eV. RbCuZrTe 3 exhibits a low thermal conductivity under 0.5 W m −1 K −1 at room temperature.

Synthesis, crystal structure, DFT, and photovoltaic studies of BaCeCuS3

“…A similar ultralow thermal conductivity value of ∼0.35 W m −1 K −1 at 573 K is reported for the structurally related RbCuZrTe 3 . 12 The rattling of relatively loosely bound Rb + cations and the distortion of Zr-coordinated octahedra in RbCuZrTe 3 are responsible for the ultralow value of the lattice thermal conductivity ( k lat ). On similar lines, it is expected that the rattling of Ba 2+ cations in the BaCeCuS 3 sample at high temperatures should also lead to low values of k lat .…”

“…15 The Kanatzidis group recently reported six new compounds of the 1113family with a general formula of ACuZrQ 3 (A = Rb, Cs; Q = S, Se, and Te). 12 An ultralow thermal conductivity value of B0.35 W m À1 K À1 was observed for a polycrystalline sample of RbCuZrTe 3 at 573 K. The ultralow thermal conductivity of this compound was attributed to the rattling of Rb + cations in the structure at high temperatures.…”

“…For instance, A or Ak atoms can be substituted by Pb/Th, and Ln atoms can be replaced by transition metals or early actinides (An), 11 which prefer octahedral coordination environments. These (A/Ak)MLnQ 3 types of structures are mainly categorized into three subtypes based on the formal oxidation state of the constituent elements: Type-I, A + M + M' 4+ (Q 2À ) 3 [M = Cu + or Ag + ; M' = Zr 4+ /Hf 4+ /Np 4+ ], 12 Type-II, Ak 2+ M + Ln 3+ (Q 2À ) 3 , 13,14 and Type-III, A 2+ M + M' 3+ (Q 2À ) 3 [M' = Sc 3+ /Y 3+ ]. 15 The electropositive A + and Ak 2+ cations in these structures mainly serve as electron donors.…”

Tunable Salt-Inclusion Chalcogenides for Ion Exchange, Photoluminescence, and Scintillation

“…Advances in synthetic chalcogenide chemistry have accelerated the discovery of functional materials as well as stimulated the development of numerous technological applications for these materials, all helped by an increased understanding of composition–property relationships. , Chalcogenide-based compounds occupy a unique position in material chemistry due to the soft nature of the chalcogen elements and emerging covalent metal chalcogenide bonding, which results in a rich and diverse crystal chemistry. , In fact, the electronic structure of chalcogenide materials favors their applications as quantum materials, catalysts, ion-exchange materials, ion-conductors, luminophores, thermoelectric materials, and semiconductors. − Recent advances in developing convenient synthetic approaches have enabled the rational synthesis of new functional chalcogenide-based materials containing a wide range of elements, resulting in various material types, ranging from nanoparticles to large single crystals of pure inorganic compositions and hybrid structures. − Another new material type that has emerged from these investigations is salt-inclusion chalcogenide materials (SICs) , that exhibit novel framework topologies and possess ionic inserts (salt-inclusions).…”

Origin of off-centering effect and the influence on heat transport in thermoelectrics

“…Compared with other well-known mechanisms, the off-centering effect has been rarely discussed. However, recent research has shown that the off-centering effect could introduce low frequency optical mode and result in strong acoustic-optical (A-O) phonon scattering, making it an effective approach to reduce the thermal conductivity [39][40][41][42].…”