Evolution of structure and transport properties of the Ba8Cu16P30 clathrate-I framework with the introduction of Ga

Abstract

Two type-I clathrates were synthesized by introducing Ga into the framework of the Ba8Cu16P30 type-I clathrate. The introduction of minute amounts of Ga, 1.9% Ga/ Mtotal (where Mtotal = Cu + Ga), resulted in the disturbance of the completely ordered Pbcn superstructure of Ba8Cu16P30. Ba8Cu15.43(2)Ga0.3P30.26(3) crystallizes in a partially ordered orthorhombic Pmna clathrate-I superstructure with five out of 15 framework sites being jointly occupied by metal+phosphorus. Increasing the Ga content resulted in all framework sites being occupied by metal + phosphorus in the archetype cubic Pm[Formula: see text] n clathrate-I crystal structure of Ba8Cu14.5(3)Ga1.3P30.2(4) with 8.2% Ga/ Mtotal. A combination of energy dispersive x-ray spectroscopy, inductively coupled plasma mass spectroscopy, and single crystal x-ray diffraction was used to determine the structures alongside the compositions. The positional disorder was verified by 31P solid state NMR spectroscopy. Characterization of the transport properties indicated that the Ga-substituted samples exhibit higher Seebeck coefficients and electrical resistivities compared to its pristine counterpart, in line with the expected reduction of the hole concentration due to Ga/Cu substitution. Moderate improvements in the thermoelectric power factor and overall figure-of-merit were observed for samples with 6.9% and 3.8% Ga/ Mtotal as compared to those for the pristine Ba8Cu16P30 clathrate. Band structure calculations shed light on how Ga substitution affects the electronic structure and thermoelectric properties of studied clathrates.

BaCuTP2 (T = Al, Ga, In): a semiconducting black sheep in the ThCr2Si2 intermetallic family

“…Due to similar X-ray scattering factors of Cu and Ga, the precision of the site occupancy determination is low. 17 The Cu : T ratio for BaCuAlP 2 and BaCuGaP 2 was close to 1 : 1 within 3 standard deviations, while the BaCuInP 2 single crystal was found to be Curich. The occurrence of the Cu : T ratio being closer to 1 : 1 with Ba(+2), Cu(+1), T(+3), and 2 P(−3) resulted in electron-balanced compositions.…”

“…Cu and Ga), establishing site preferences using X-ray diffraction is challenging due to similarities of X-ray scattering factors. 16,17 Most of the materials from the ThCr 2 Si 2 family are metallic in nature with a partially lled transition metal d-band. 18 The formation of vacancies at the M-site is common for compounds of late transition metals, such as ACu 1.7-1.9 Pn 2 (A = Ca, Sr, Eu; Pn = P, As) 19,20 and RENi 1.7-1.9 P 2 (RE = La, Ce, Pr).…”

Organizing Chaos: Boosting Thermoelectric Properties by Ordering the Clathrate Framework of Ba8Cu16As30

“…The Seebeck coefficient of mP 108-Ba 8 Cu 16 As 30 increased linearly from 108 μV/K at 300 K to 162 μV/K at 573 K. Compared to Ba 8 Cu 16 P 30 , which has a Seebeck coefficient of ∼30 μV/K at 573 K, Ba 8 Cu 16 As 30 exhibits a 5-fold increase. The thermoelectric performance enhancement of Ba 8 Cu 16 P 30 has been well explored with the substitution of Zn, Au, Ga, and Ge into the framework as well as the substitution of Ba with La, Ce, and Eu. ,,− These studies have paved a pathway that may be followed for future thermoelectric enhancement of Ba 8 Cu 16 As 30 .…”

BaCu2SiS4: A New Member of the AIIBI2MIVQ4 Chalcogenide Family with a Chiral Crystal Structure

“…Fluxes may help to bypass the formation of unwanted side products and promote crystal growth. [21][22][23]34,[39][40][41] AB 2 MQ 4 (A = divalent metal; B = monovalent metal; M = tetrel = Si, Ge, or Sn; Q = chalcogen) is a family of quaternary chalcogenides that encompasses numerous noncentrosymmetric structure types, with applications ranging from nonlinear optics to photovoltaics. [42][43][44][45][46][47][48][49][50] A new member of this family, BaCu 2 SiS 4 , was discovered while trying to synthesize a hypothetical electron-balanced clathrate-I, [51] Ba 8 Cu 18 Si 9 S 19 , in salt flux.…”

“…One promising synthetic approach is performing reactions in a liquid media, such as a molten salt flux. Fluxes may help to bypass the formation of unwanted side products and promote crystal growth [21–23,34,39–41] …”