Preferentially oriented Fe-doped CaCu3Ti4O12 films with high dielectric constant and low dielectric loss deposited on LaAlO3 and NdGaO3 substrates

The colossal dielectric constant of calcium copper titanate (CCTO) thin films is generally accompanied by high dielectric losses which limit its potential for electronic miniaturization. Strategies for reducing the dielectric loss while keeping large dielectric constants are needed for various electrical applications of CCTO. This work aims to reduce the loss by means of doping preferentially oriented CCTO films with Fe3+ ions. Highly oriented undoped and Fe-doped calcium copper titanate (Fe-doped CCTO) thin films were fabricated by synthesizing CCTO on LaAlO3(1 0 0) and NdGaO3(1 0 0) substrates via a sol-gel spin casting method. The films with different Fe-doping concentrations (0, 1.6 and 2.6 wt%) were structurally and chemically characterized via energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. X-Ray Diffraction (XRD) patterns confirmed that our doped CCTO films had a cubic perovskite structure with well-defined preferential orientations of (h00) and (hh0) on LAO and NGO substrates, respectively. Preferentially oriented films having room temperature dielectric constants on the order of 1000 in conjunction with values of loss tangent smaller than 0.012 in the frequency range of 50 Hz-2 MHz were achieved. Temperature dependence of the dielectric constant and loss tangent revealed that Fe-doping decreased the dielectric loss via the lowering of the electrical conduction through CCTO grains.Fil: Pongpaiboonkul, Suriyong. Chulalongkorn University; TailandiaFil: Daniels, Thitima M.. National Electronics and Computer Technology Center; TailandiaFil: Hodak, Jose Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Wisitsoraat, Anurat. National Electronics and Computer Technology Center; TailandiaFil: Hodak, Satreerat K.. Chulalongkorn University; Tailandi

Enhancement of H2S-sensing performances with Fe-doping in CaCu3Ti4O12 thin films prepared by a sol-gel method

In this work, the effects of Fe-doping on structural and gas-sensing properties of CaCu3Ti4O12 (CCTO) thin film prepared by a sol-gel method were systematically studied. Sol-gel-derived CCTO thin films with different Fe-doping concentrations were deposited on alumina substrates by spin-coating and Au/Cr interdigitated electrodes were patterned onto the films by photolithography, sputtering and lift-off processes. Characterizations by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and X-ray absorption near edge structure confirmed the perovskite CCTO phase with TiO2 and CuO secondary phases and suggested the substitution of Fe3+ ions at Ti4+ sites of CCTO structure. From gas-sensing measurements, Fe dopants greatly enhance H2S response, response time and H2S selectivity against NH3, CO, C2H2, CH4, ethanol and NO2. In particular, 9 wt% (∼3 at%) Fe-doped CCTO sensor exhibited the highest response of ∼126 to 10 ppm H2S, which was more than one order of magnitude higher than that of the undoped CCTO sensor at a low optimum operating temperature of 250 °C. The roles of Fe-dopant on gas-sensing mechanisms of CCTO sensor were proposed.Fil: Pongpaiboonkul, Suriyong. Chulalongkorn University; TailandiaFil: Phokharatkul, Ditsayut. Nanoelectronics and MEMS Laboratory; TailandiaFil: Hodak, Jose Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Chulalongkorn University; TailandiaFil: Wisitsoraat, Anurat. Nanoelectronics and MEMS Laboratory; TailandiaFil: Hodak, Satreerat K.. Chulalongkorn University; Tailandi

Controlling the preferential orientation in sol-gel prepared CaCu3Ti4O12 thin films by LaAlO3 and NdGaO3 substrates

Researchers have paid considerable attention to CaCu3Ti4O12 (CCTO) due to the colossal dielectric constant over a wide range of frequency and temperature. Despite of the growing number of works dealing with CCTO, there have been few studies of the role played by the substrate in inducing structural and dielectric effects of this material. In this work, highly-oriented CCTO thin films have been deposited on LaAlO3(100), NdGaO3(100) and NdGaO3(110) substrates using a sol-gel method. These single crystal substrates were chosen in terms of small lattice mismatch between CCTO and the substrate. The X-ray diffraction patterns showed that the CCTO film layers grow with different orientations depending upon the substrate used. We show that the preferred orientation of CCTO thin films can be manipulated to a high degree by growing it on specific crystal planes of the substrates without the use of buffer layers. Colossal dielectric constants are observed in our films which appear to correlate with the film crystallinity and preferred orientation.Fil: Pongpaiboonkul, Suriyong. Chulalongkorn University; TailandiaFil: Kasa, Yumairah. Chulalongkorn University; TailandiaFil: Phokharatkul, Ditsayut. Nanoelectronics and MEMS laboratory; TailandiaFil: Putasaeng, Bundit. Thailand Science Park; TailandiaFil: Hodak, Jose Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Chulalongkorn University; TailandiaFil: Wisitsoraat, Anurat. Nanoelectronics and MEMS laboratory; TailandiaFil: Hodak, Satreerat K.. Chulalongkorn University; Tailandi