Transport and band structure studies of crystallineZnRh2O4

Abstract

We report the synthesis and characterization of non-d 10 p-type transparent conducting oxides of the normal spinel ZnRh 2 O 4 . Undoped ZnRh 2 O 4 was successfully prepared by means of bulk solid-state synthesis. The conduction mechanism and bulk defect chemistry of polycrystalline sintered pellets of ZnRh 2 O 4 were studied through electrical conductivity and Seebeck coefficient measurements, in defect equilibrium at elevated temperature under controlled atmospheres. Optical diffuse reflectance measurements were also carried out to evaluate band gap. The data were analyzed in terms of an activated mobility ͑small polaron conduction͒, with a hopping energy of 0.25 eV. Results from band structure calculations by LDA+ U and optical band-gap measurement by UV-visible spectrometry are in good agreement with literature data.

Conducting mechanism in the epitaxialp-type transparent conducting oxideCr2O3:Mg

“…Hall measurements were performed in a physical property measurement system with field sweeps up to 14 T. However, it was not possible to extract a meaningful value for the Hall coefficient due to the thermal instability being greater than the signal. Using the thermoelectric measurements, it is possible to estimate the Seebeck mobility of thin films [11,33,41,49,60].…”

“…However Cu-delafossites have proven to be hindered by their small-polaron hopping (SPH) mechanism, high deposition temperature, and, in some cases, interband transitions limiting their transparency [10]. Spinel p-type TCOs such as ZnRh 2 O 4 , despite the advantage of retaining their conductivity as amorphous thin films, have relatively low conductivity [11] (0.1 Scm −1 ). Similarly the distorted delafossite SrCu 2 O 2 also has low conductivity [12] (0.053 Scm −1 ).…”

“…The carriers move by "hopping" to available sites. Small polaron conduction is unfavorable for a p-type TCO as they are usually associated with high carrier concentrations (>10 21 cm −3 ) [11] and correspondingly low mobilities. The present paper allows us to verify the conduction mechanism in a less complex binary oxide system, to understand the microscopic charge transport mechanism, and to outline paths to increase the mobility in the material.…”

Spray pyrolysis growth of a high figure of merit, nano-crystalline, p-type transparent conducting material at low temperature

“…The polaronic nature of CuCrO 2 has already been reported extensively 33 and motivated by this we use the SPH model to estimate a mobility value. Within this model the Seebeck coefficient can be used as a direct mea- sure of the fraction of occupied carrier sites 7,9 , c. This is related to the carrier concentration p by p=Nc, where the density of conducting sites N can be calculated using the unit cell volume of the CuCrO 2 crystal and the number of Cu atoms per unit cell (2.5×10 22 cm −3 ). From this p it is possible to estimate a mobility of 6.4×10 −3 cm 2 /Vs for a sample with a conductivity of 12 S/cm (the highest conductivity at room temperature for our films).…”

“…5 Since then the field has extended to other materials such as oxychalcogenides, spinels and α-Cr 2 O 3 . [6][7][8][9] One of the delafossites, CuCrO 2 , has shown promise as a p-type TCM due to reports of high conductivity when doped with Mg. 10 However this is typically only achieved by physical vapour deposition (PVD) which is a relatively slow and costly technique in comparison to other depostion methods. CuCrO 2 has also been grown by chemical vapour deposition (CVD) using the metal-organic Acetylacetonate (acac) precursors Cr(acac) 3 and Cu(acac) 2 at 550 • C, resulting in polycrystalline films with conductivity of 0.86 S/cm (figure of merit (FOM) ≈ 45 µS).…”