The local atomic structure and thermoelectric properties of Ir-doped ZnO : hybrid DFT calculations and XAS experiments

• We combined the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments in the study of the local atomic structure around Ir ions in ZnO thin films with different iridium content. This was then used in the first principles analysis of the thermoelectric properties of material. The emphasis has been put on the conditions for a positive Seebeck coefficient and p-type electrical conductivity as the functions of the Fermi level. We studied both computationally and experimentally several possible IrOxpolyhedra (complexes) with a different number of surrounding oxygens and Ir oxidation states, including those with the formation of peroxide ions (O22−). In particular, octahedral coordination of iridium ions was identified by reverse Monte Carlo (RMC) simulations of the Ir L3-edge EXAFS spectra of ZnO:Ir thin films as the predominant complex, which is supported by the calculated lowest interstitial oxygen incorporation energies. All the calculated IrOx(x= 4, 5, 6) complexes, regardless of Ir the oxidation state, demonstrate potential for p-type conduction if the Fermi level (μF) falls in the range of 0-0.8 eV from the valence band maximum (VBM) and the Ir concentration is high enough (12.5% in the present DFT calculations). Even though the corresponding calculated Seebeck coefficient (S) around 80-89 μV K−1slightly exceeds the experimental values, we emphasise the presence of an important plateau in the dependence ofSonμFin this range for two complexes with the formation of peroxide ions (O22−). We predicted also that peroxide ions O22−are characterized by the calculated phonon frequencies of 810-942 cm−1in agreement with our previous Raman experimental results. In this light, we discuss the high sensitivity of calculatedS(μF) dependences to the atomic and electronic structure. 

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

NATURVETENSKAP  -- Kemi -- Materialkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Materials Chemistry (hsv//eng)

Nyckelord

Atoms

Calculations

Coordination reactions

Electronic structure

Fermi level

II-VI semiconductors

Ions

Iridium

Monte Carlo methods

Oxidation

Oxide minerals

Peroxides

Seebeck coefficient

Thermoelectric equipment

Thermoelectricity

Thin films

X ray absorption spectroscopy

Zinc oxide

Electrical conductivity

Experimental values

Interstitial oxygen

Local atomic structures

Octahedral coordination

Reverse monte carlo simulation

Thermoelectric properties

Valence-band maximums

Density functional theory

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