Structural and electrical properties of delafossite CuMO2 (M=Al, Cr, Y) semiconductors and their exploitation for ozone detection

Single phase polycrystalline pellets of CuMO2 (M = Al, Cr, Y) semiconductors with delafossite structure were prepared by sol-gel method and solid state reaction, respectively. The XRD results shows that structure can be indexed as 3R-CuAlO2 (JCPDF No. 35-1401), 3R-CuCrO2 (JCPDF No. 89-6744) and 2H-CuYO2 (JCPDF No. 76-1422), respectively. The conductivities of CuMO2 are thermally activated in the measured temperature range with the activation energy EA about 0.24eV, 0.34eV and 0.25eV, respectively. The conductivities of CuMO2 decrease monotonously with the increase of radius of M cation. This phenomenon coincides with the previous theoretical studies that the hole conduction path of CuMO2 was predominantly in the Cu-ions layers, and the Cu-Cu spacing (or α-axis length) was governed by the M cation size, which modifies the wave function overlap between Cu-ions and results in decrease of the conductivities. The room temperature ozone sensing properties of CuMO2 (M = Al, Cr, Y) polycrystalline pellets were studied. Ozone-purified air-ozone circles were used to measure the ozone gas sensing properties of all the specimens, which are similar to the practical measurement environments. The relative humidity of the environment was controlled around 60 RH% ± 5 RH%. The temperature was controlled around 300K ± 0.5K. Except for CuYO2 pellets, CuAlO2 and CuCrO2 pellets show reversible responds to ozone gas at room temperature. The room temperature ozone sensing properties of CuCrO2 film prepared by pulsed laser deposition was also studied. The response time of CuCrO2 film is about 3.5 min to 90% of the final value and the recovery time is about 2 min to 10% of the steady state signal under ozone concentration of 600 ppm. Though the performance is not yet sufficiently high for practical use, the delafossites CuMO2 (M = Al and Cr), as parent compounds of room temperature ozone sensing materials, are recommendable for further studies on the improvement of ozone sensing properties.