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Electronic band structure and low-temperature transport properties of the type-I clathrate Ba8NixGe46-x-yy

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Aydemir,  U.
Chemical Metal Science, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Candolfi,  C.
Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Ormeci,  A.
Chemical Metal Science, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Baitinger,  M.
Michael Baitinger, Chemical Metal Science, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Burkhardt,  U.
Ulrich Burkhardt, Chemical Metal Science, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Oeschler,  N.
Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Steglich,  F.
Frank Steglich, Physics of Quantum Materials, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Grin,  Yu.
Juri Grin, Chemical Metal Science, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Citation

Aydemir, U., Candolfi, C., Ormeci, A., Baitinger, M., Burkhardt, U., Oeschler, N., et al. (2015). Electronic band structure and low-temperature transport properties of the type-I clathrate Ba8NixGe46-x-yy. Dalton Transactions, 44(16), 7524-7537. doi:10.1039/c4dt03827d.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0026-DC37-D
Abstract
We present the evolution of the low-temperature thermodynamic, galvanomagnetic and thermoelectric properties of the type-I clathrate Ba8NixGe46-x-y square(y) 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 x 2a x 2a supercell described in the space group Ia (3) over bard for x <= 1.0 and a primitive unit cell a x a x a (space group Pm (3) over barn) 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-x-y square(y) therefore provides an excellent experimental platform to probe the evolution of the peculiar properties of the parent type-I clathrate Ba8Ge43 square(3) upon Ge/Ni substitution and filling up of the vacancies, which might be universal among the ternary systems at low substitution levels.