Structure, Properties And LITV Effect Of Mg-doped CuCrO₂ Polycrystalline And Thin Films

CuCrO₂ is a transparent conductive oxide material with wide band gap(E_g>3.1e V),belonging to delafossite structure.The material is a classical layer structure with close-packed Cu⁺layers and edge-sharing CrO₆ octahedral layers alternative stacking along the c-axis.Due to its obvious layered structure,the material system may have strong transport anisotropy.Mg doping can improve the conductivity and anisotropy of CuCrO₂material,and high quality CuCr_1-xMg_xO₂(x=0,0.01,0.02,0.03,0.05)polycrystals and thin films were prepared in this paper.We studied microstructure,chemical valence state,thermal property,electrical property and transport anisotropy.The Mg doping effect has been discussed.The laser-induced thermoelectric voltage(LITV)effect in CuCr_1-xMg_xO₂ inclined delafossite thin films was observed.The physical mechanism of the LITV signal characteristics has been analyzed.The time response characteristics of signals and the correlation between decay time and thermal conductivity have been discussed.C-axis inclined CuCr_1-xMg_xO₂(x=0?0.05)polycrystals were prepared by solid-state reaction at 1100?/12h+1100?/12h.The phase structure,layer grain growth,orientation and chemical state of elements were characterized by XRD,SEM,TEM and XPS.After Mg doping,the layered grains grow significantly and polycrystals tend to grow along the c-axis,which the Lotgering Factor is F_(00l)=0.90 in CuCr_0.97Mg_0.03O₂ samples.The resistivity-temperature(?-T)curves show that they are semiconductor-like behavior(d?/d T<0)in accordance with Arrhenius thermal activation mode,and the resistivty decreased by 3 orders of magnitude after Mg doping.The thermal activation energy decreases significantly,indicating that Mg doping forms an acceptor level,which induces hole carriers in the valence band.This is consistent with the results in XPS,Mg doping induces Cu²⁺in Cu⁺layer.The growth of layer grains along ab plane and the reduction of grain boundaries and defects,which also increases the average free path of carriers.The thermal conductivity-temperature(?-T)dependence shows the range of?is 5-12 W/m·K.The?increses after Mg doping,within the doping amount increases,the thermal conductivity decreases slightly due to the generation of impure phase.The?decreases with the increase of T.Furthermore,the thermal conductivity contribution of Cu MO₂polycrystals is studied,which is more than 98%.C-axis inclined CuCr_1-xMg_xO₂ epitaxial thin films were prepared by pulsed laser deposition on 0°/5°/10°?-Al₂O₃(0001)single crystal substrates.The inclined angles of films have been detected.The step-flow growth morphology of 0°/10°inclined thin films was observed by AFM.Films all show semiconductor transport behavior.The resistivity decreases and resistivity anisotropy increases with Mg doping,which is attributed to Cu²⁺ions are induced in the Cu⁺layers and more holes produced via a charge-compensating process.It can enhance the electric transport of in-plane films.The LITV signals of CuCr_1-xMg_xO₂ films under different Mg doping amount,tilted angle and laser energy density were studied.The LITV signals increases by Mg doping,mainly because it increases the resistivity anisotropy and seebeck coeficient anisotropy of the films.A LITV signal of 156m V(under laser energy density 117m J/cm²)was observed in 10°inlined CuCr_0.98Mg_0.02O₂films.We discussed the long decay time of voltage signal,the main reason is the absolute dominant phonon thermal conductivity.