The solid solution series Tl(V_1−xCr_x)₅Se₈: crystal structure, magnetic and thermoelectric properties

Abstract

The crystal structure of single crystalline members of the solid solution series Tl(V 1Àx Cr x ) 5 Se 8 (x = 0-1 and Dx = 0.2) was determined and the magnetic and thermoelectric properties of bulk TlV 5 Se 8 were investigated. All compounds crystallize in the pseudo-hollandite-type structure (C2/m) with a nonlinear increase in the unit cell volume due to a simultaneous increase/decrease in the transition metal distances across the edge/face-sharing octahedra. A slight Tl deficiency was found for single crystalline TlV 5 Se 8 and Tl(V 0.8 Cr 0.2 ) 5 Se 8 as well as for bulk TlV 5 Se 8 according to Rietveld and single crystal structure refinements.The metallic character of bulk TlV 5 Se 8 and its low electrical resistivity compared to poly-and singlecrystalline TlCr 5 Se 8 can probably be associated with this probable Tl deficiency. In TlV 5 Se 8 , anomalies in the low temperature Seebeck coefficient, i.e. a maximum at T B 14 K and two sign changes at T B 47 K and T B 167 K, were found. Bulk TlV 5 Se 8 is a highly frustrated (f = |y|/T N E 42 K) Curie-Weiss paramagnet ordering antiferromagnetically (y = À1287 K) below T N E 31 K with an effective magnetic moment of m = 2.68 m B corresponding to V 3+ . Low-field M(H) measurements revealed the existence of a small ferromagnetic component below T N in bulk TlV 5 Se 8 and, despite the observed spin frustration, no spin glass phase was found in this compound.

Resonant Bonding, Multiband Thermoelectric Transport, and Native Defects in n-Type BaBiTe3–xSex (x = 0, 0.05, and 0.1)

“…BaBiTe 3 is an ideal candidate for fulfilling the requirements of a phonon glass and an electron crystal, which according to Slack results in both a low thermal and a high electrical conductivity needed for thermoelectrics . The rigid, one-dimensional [Bi 4 Te 10 ] ∞ rods in the structure allow facile electronic conduction, while the heavy Ba atoms and weak Te···Te bonding result in a low thermal conductivity similar to previously studied compounds containing Ba or Tl. − In addition, the electrostatic repulsion between the lone pairs of Bi and the neighboring Te atoms can lead to strong anharmonicities in the lattice vibrations and hence low phononic thermal conductivities (κ ph ) close to the amorphous limit. − Low-temperature thermoelectric measurements of both p- and n-type single crystalline BaBiTe 3 and electronic band structure calculations gave a first impression of its promising thermoelectric properties. A pressure dependent study of the thermoelectric properties of p-type BaBiTe 3 single crystals and a recent study of K and La substituted variants of BaBiTe 3 showed it was of further interest.…”

Crystal structures of the four new quaternary copper(I)-selenides A0.5CuZrSe3 and ACuYSe3(A=Sr, Ba)

“…[1][2][3][4] These open structural frameworks can be obtained by a charge transfer from strong cations such as Sr and Ba towards an anionic network containing transition metals and Se/Te. Copper chalcogenides are of particular interest due to the high Cu mobility, which can result in a "phonon-liquidelectron-crystal" type behavior, low heat capacities, structural disorder, fast ion conduction, superionicity and promising thermoelectric properties.…”

Substitution of indium for chromium in TlIn5−xCrxSe8: crystal structure of TlIn4.811(5)Cr0.189(5)Se8

“…Monoclinic TlCr 5 Se 8 and the related triclinic compound Ba 0.5 Cr 5 Se 8 have thermal conductivities well below 1 W m À1 K À1 from room temperature to 873 K (Lefè vre et al, 2015(Lefè vre et al, , 2016. As part of our project, we successfully synthesized a solid solution of TlV 5-x Cr x Se 8 (x = 0, 1, 2, 3, 4, 5) and studied the magnetism and thermoelectric properties of TlV 5 Se 8 (Maier et al, 2015).…”