Rapid synthesis and electrical transition in p-type delafossite CuAlO₂

Abstract

Highly polycrystalline and pure delafossite phase CuAlO 2 powder has been synthesised within a short annealing period, shorter than most conventional processes. This is an improvement over the conventional synthesis procedures. Conventional synthesis procedure has seen CuAlO 2 only formed at high annealing temperatures ≥ 1100°C over long annealing time, some as long as 96 hours. In the current process, a pure phase devoid of impurities has been obtained at reduced calcination time of 1.5 hours in an argon atmosphere at a temperature of 1150°C. This was confirmed by XRD and SEM/EDX. High temperature DC/AC electrical measurements show a change in conduction mechanism from mixed conductivity (ionic + p-type) in the temperature range of 375 ≥ T ≥ 25°C to intrinsic type behavior above 375°C. The activation energies for these two regimes are 0.27 eV and 0.08 eV respectively. This change from mixed to DC conductivity is confirmed by spectral analysis too. Spectral analysis using the power law also revealed that conduction is of long range hopping. Use of platinum as a contact electrode at elevated temperatures has a detrimental effect on the electrical properties since it encourages the formation of CuAl 2 O 4 at the interface due to the formation of more stable Cu−Pt alloy by virtue of the chemical reaction Pt + 2CuAlO 2 − → CuAl 2 O 4 + Pt Cu .

Synthesis of CuAlO2 from chemically precipitated nano-sized precursors

“…In addition, CuAlO 2 exhibits anisotropic behaviour in terms of electrical conductivity and the random orientation of the grains has a negative effect on the conductivity [1,52]. The electrical conductivity of the sample produced at 1150 °C in this study is comparable with the previously reported results in the literature using air atmosphere sintering at temperatures above 1100 °C [18,27,38] …”

“…The difficulty in achieving reduced temperature formation stems from the thermodynamic instability of CuAlO 2 below 1000 °C in air, yielding CuO and CuAl 2 O 4 phases involving Cu 2+ cation [37]. In a recent study, it was shown that the reaction times could significantly be reduced by flowing argon during firing [38]. CuAlO 2 was obtained via solid state reaction in 1.5 h via isothermal firing at 1150 °C and inert atmosphere quenching.…”

Thermodynamic investigations on the growth of CuAlO2 delafossite crystals

“…Problems occurring with CuO x melts in Pt crucibles were already reported by several authors, e.g. [25,26] and are related to the formation of solid solutions between Pt and Cu. Both metals crystallize in f cc structure and the binary phase diagram Cu-Pt is in the high T range > 1000 • C almost ideal.…”

Localized Surface Plasmon Resonance Absorption Generated by Free Carriers in Zn‐Doped CuGa1−xZnxO2 Nanoplates

“…The copper‐based delafossite oxide semiconductors CuMO 2 (M = Cr, Ga, Al) have become much attractive in recent years due to their room‐temperature p‐type conductivity and wide direct bandgap . These characteristics are favorable for constructing p–n junction and have promising applications in optoelectronics .…”

“…The copper-based delafossite oxide semiconductors CuMO 2 (M ¼ Cr, Ga, Al) have become much attractive in recent years due to their room-temperature p-type conductivity and wide direct bandgap. [1][2][3][4][5][6] These characteristics are favorable for constructing p-n junction and have promising applications in optoelectronics. [7] The intrinsic p-type conductivity in CuMO 2 is attributed to the ionized interstitial oxygen atoms and ionized Cu vacancies.…”