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Issue 16, 2015
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Electronic band structure and low-temperature transport properties of the type-I clathrate Ba8NixGe46−xyy

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Abstract

We present the evolution of the low-temperature thermodynamic, galvanomagnetic and thermoelectric properties of the type-I clathrate Ba8NixGe46−xyy with the Ni concentration studied on polycrystalline samples with 0.0 ≤ x ≤ 6.0 by means of specific heat, Hall effect, electrical resistivity, thermopower and thermal conductivity measurements in the 2–350 K temperature range and supported by first-principles calculations. The experimental results evidence a 2a × 2a × 2a supercell described in the space group Ia[3 with combining macron]d for x ≤ 1.0 and a primitive unit cell a × a × a (space group Pm[3 with combining macron]n) above this Ni content. This concentration also marks the limit between a regime where both electrons and holes contribute to the electrical conduction (x ≤ 1.0) and a conventional, single-carrier regime (x > 1.0). This evolution is traced by the variations in the thermopower and Hall effect with x. In agreement with band structure calculations, increasing the Ni content drives the system from a nearly-compensated semimetallic state (x = 0.0) towards a narrow-band-gap semiconducting state (x = 4.0). A crossover from an n-type to a p-type conduction occurs when crossing the x = 4.0 concentration i.e. for x = 4.1. The solid solution Ba8NixGe46−xyy therefore provides an excellent experimental platform to probe the evolution of the peculiar properties of the parent type-I clathrate Ba8Ge433 upon Ge/Ni substitution and filling up of the vacancies, which might be universal among the ternary systems at low substitution levels.

Graphical abstract: Electronic band structure and low-temperature transport properties of the type-I clathrate Ba8NixGe46−x−y□y

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Publication details

The article was received on 13 Dec 2014, accepted on 14 Mar 2015 and first published on 17 Mar 2015


Article type: Paper
DOI: 10.1039/C4DT03827D
Dalton Trans., 2015,44, 7524-7537

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    Electronic band structure and low-temperature transport properties of the type-I clathrate Ba8NixGe46−xyy

    U. Aydemir, C. Candolfi, A. Ormeci, M. Baitinger, U. Burkhardt, N. Oeschler, F. Steglich and Yu. Grin, Dalton Trans., 2015, 44, 7524
    DOI: 10.1039/C4DT03827D

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