Effect of metal doping on the low-temperature structural behavior of thermo electric beta-Zn4Sb3

• The low-temperature structural phase transitions of Bi, Pb, In and Sn-doped samples of thermoelectric Zn4Sb3 have been characterized on crystals grown from molten metal fluxes, using electrical resistance and single crystal X-ray diffraction measurements. Room temperature stable, disordered, beta-Zn4Sb3 undergoes two phase transitions at 254 and 235 K to the consecutively higher ordered phases a and alpha', respectively. The ideal crystallographic composition of alpha-Zn4Sb3 is Zn13Sb10. The alpha-alpha' transformation is triggered by a slight and homogenous Zn deficiency with respect to this composition and introduces a compositional modulation in the alpha-Zn4Sb3 structure. When preparing beta-Zn4Sb3 in the presence of metals with low melting points (Bi, Sn, In, Pb) the additional metal atoms are unavoidably incorporated in small concentrations (0.04-1.3 at%.) and act as dopants. This incorporation alters the subtle balance between Zn disorder and Zn deficiency in Zn4Sb3 and has dramatic consequences for its low-temperature structural behavior. From molten metal flux synthesis it is possible to obtain (doped) Zn4Sb3 samples which (1) only display a P-a transition, (2) only display a beta-alpha' transition, or (3) do not display any low-temperature phase transition at all. Case (2) provided diffraction data with a sufficient quality to obtain a structural model for highly complex, compositionally modulated, alpha'-Zn4Sb3. The crystallographic composition of this phase is Zn84Sb65.

Nyckelord

temperature polymorphism

Thermoelectric materials

zinc antimonides

order-disorder structural transitions

initio structure solution

thermoelectric properties

solid-solutions

phonon-glass

zn4sb3

zinc

transitions

stability

phases

figure

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