Structure and Physical Properties of Clathrate I Systems Ba₈Pd_xSi_46-xand Ba₈Pt_xSi_46-x

Abstract

Phase relations at 900• C, crystal chemistry, electrical and thermal transport measurements, and heat capacity data are reported for the clathrate systems: Ba8{Pd, Pt}xSi46−x. For both systems a ternary clathrate phase was identified with a small homogeneity region extending at 900• C for 2.5 ≤ x P d ≤ 4.1 and 2.8 ≤ xP t ≤ 4.9, respectively. Structural investigations of these clathrate phases at 300, 200 and 100 K define cubic primitive symmetry with the space group type P m3n consistent with clathrate type I. Studies of electronic and thermal transport groups both series of compounds close-by a semiconducting state. An sizeable charge carrier concentration in these systems, however, prevents sufficiently large thermopower values. In comparison to isostructural type I clathrates based on Ge, thermal conductivity -dominated by the lattice contribution -is larger due to the smaller mass of Si.

Single-Crystal Investigations on Quaternary Clathrates Ba8Cu5Si x Ge41−x (x = 6, 18, 41)

“…Cu atoms occupy the 6d (¼, ½, 0) site, as always observed for transition-metal (TM) elements in the ''Cordier'' clathrate compounds. [19][20][21][22][23][24][28][29][30][31] In the germanides Ba-TM-Ge, in addition to TM elements, also vacancies, present for TM contents below six atoms per unit cell, accumulate at the 6d site. [20][21][22][23][24][31][32][33] In the silicides Ba-TM-Si, vacancies have been revealed only in a few cases.…”

“…[20][21][22][23][24][31][32][33] In the silicides Ba-TM-Si, vacancies have been revealed only in a few cases. 19,29,30,34 We tried to determine whether vacancies are present in our mixed Ge and Si samples by refinements from the SCXD data using two different structure models. In both models we had, due to the very similar scattering factors for Cu and Ge, to fix the Cu content to 5, the value determined from our EDX measurements.…”

“…A number of investigations have been performed to elucidate the fundamental mechanism of the low thermal conductivity in clathrates by either varying the guest atoms [7][8][9][10][11][12] or changing the environment of the guest atoms by substitution of host atoms. 9,11,[13][14][15][16][17][18][19][20][21][22][23][24] Herein, we report our investigations on the type I clathrates Ba 8 Cu 5 Si x Ge 41Àx (x = 6, 18, 41) with the aim of clarifying the structural details and their variation with x, by single-crystal x-ray diffraction.…”

Ba-Cu-Si Clathrates: Phase Equilibria and Crystal Chemistry

“…Similar phase relations to the clathrate phase can also be found in other Ba-TM-Si Table I. systems. 28 Figure 3 shows microstructures of the annealed alloys Ba 8 Cu 3 Si 43 , Ba 8 Cu 6 Si 40 , Ba 10 Cu 8 Si 82 , and Ba 25 Cu 5 Si 70 (a-d, respectively).…”

Novel silicide BaPt5Si12: Crystal structure and physical properties

“…Our recent investigation of the ternary system Ba-Pt-Si [1] revealed (i) the absence of a BaPt 4 Si 12 skutterudite (as found for the homologous superconducting BaPt 4 Ge 12 [2]), but (ii) the formation of a novel compound with composition BaPt 5 Si 12 and hitherto unknown structure. Indexation of the X-ray single crystal diffraction data resulted in a monoclinic unit cell with a ¼ 0.61246(1) nm, b ¼ 3.23610(4) nm, c ¼ 0.61151(1) nm, b ¼ 90.115 (2) .…”