PO 2 dependant resistance switch effect in highly epitaxial (LaBa)Co2O5+δ thin films

Abstract

Giant resistance switching behavior in mixed conductive ͑LaBa͒Co 2 O 5+␦ epitaxial thin film were discovered in high temperature and reducing environments during the reduction and reoxidation process. A reproducible resistance response of over 99% was achieved in the films during a change of 4% H 2 / 96% N 2 to oxygen at temperature range of 400-780°C. The results indicate that at, low oxygen partial pressure, the extension of oxygen deficiency is an essential factor to the high temperature physical properties of ͑LaBa͒Co 2 O 5+␦ and demonstrates its potential application as a chemical sensor device for reducing environments at high temperature. © 2010 American Institute of Physics. ͓doi:10.1063/1.3484964͔Cobalt based perovskite oxides have received increasing attention in the past decade due to their high mixed ionicelectronic conductivity in chemical sensor and green energy device development.1,2 Recent studies indicate that oxygen deficient doped double perovskite cobaltates ͑LnBa͒Co 2 O 5+␦ ͑Ln= La, Pr, Gd͒ have excellent mixed ionic-electronic conductivity with a fast surface exchange coefficient. [3][4][5] In this family of compounds, the A-site cationic ordered arrangement is favored due to the large difference in Ba 2+ and rare earth ionic radii, except ͑LaBa͒Co 2 O 5+␦ ͑LBCO͒. In LBCO, the doped bivalent Ba 2+ is not only inducing plenty of oxygen deficiency but also structurally providing the capability to achieve the smallest oxygen deficiency in this family of compounds due to the very similar ionic radii between Ba 2+ and La 3+ . Therefore, LBCO provides a unique platform with the geometrical stabilized perovskite phase and a wide range of oxygen deficiency, which enables one to study the electrical conductivity, defect structures and stability at high temperature over a wide range of oxygen partial pressure.Up to now, studies on LBCO are only limited to the bulk polycrystalline samples for low temperature transport and magnetic properties.6-8 The high temperature physical properties of LBCO are rarely studied due to the structure failure of the bulk material in a reducing environment. Recently, we have fabricated epitaxial single crystalline LBCO thin films on ͑001͒ LaAlO 3 ͑LAO͒, enabling one to systematically study the electrical transport properties of LBCO under various environments. A reproducibly dramatic resistance change is observed as the LBCO film is exposed to oxidizing and reducing environment over a wide range of temperature. Especially, it is interesting to note that the re-oxidation of the LBCO film has a very short response time, suggesting that an exceedingly fast oxygen exchange rate occurs at the film surface.A KrF excimer pulsed laser deposition system with a wavelength of 248 nm was employed to deposit the ͑LaBa͒Co 2 O 5+␦ thin films on ͑001͒ LaAlO 3 substrates. An energy density of 2.0 J / cm 2 and a laser repetition rate of 5 Hz were adopted during film deposition. A high density, single phase, stoichiometric ͑LaBa͒Co 2 O 5+␦ target was purchased from Praxair Inc. The deposit...

Gas Sensing Properties of Epitaxial LaBaCo2O5.5+δ Thin Films

“…3(a). It is clearly seen that the resistance of LBCO thin film increase when it is exposed to the ethanol vapor (reducing gas), then the resistance decrease when the gas change from 1000 ppm ethanol vapor to air, which is in agreement with our previous studies under the gas switch between H 2 and O 2 1623. In fact, the LBCO thin films will generate a high density of oxygen vacancies when it is exposed to the reducing gas53, such as ethanol vapor gas.…”

“…Recently, highly epitaxial single crystalline LBCO thin films were fabricated on various substrates, such as (001) LaAlO 3 (LAO)16, (001) SrTiO 3 171819, (001) MgO2021, and (110) NdGaO 3 22. The LBCO films not only exhibit a much larger magnetoresistance value than those from various phases of its bulk material, but also possess an extraordinary sensitivity to H 2 and O 2 , especially an exceedingly fast redox reaction at high temperature and a superfast oxygen vacancy exchange diffusion chemical dynamics1623. Therefore, the LBCO thin films are one promising candidate for the development of the gas sensors in reducing/oxidizing environments, which is one of the critical research issues in the public safety and energy security.…”

“…However, there are very few reports on the gas-sensing materials using p -type oxide semiconductor, such as NiO373839, CuO40, LaFeO 3 41, Co 3 O 4 ,4243444546474849505152535455 LBCO1623. Compared with n-type oxide semiconductor for gas-sensing, the p-type oxide semiconductors with distinctive surface reactivity and oxygen adsorption can enhance gas selectivity, decrease the dependence of humidity to negligible level and improve the recovery speed, reviewed by Kim and Lee46.…”

Thickness effects on the magnetic and electrical transport properties of highly epitaxial LaBaCo2O5.5+δ thin films on MgO substrates

“…Therefore, highly epitaxial thin films offer an alternative route to explore the nature of these physical phenomena. [20][21][22] However, it is well known that the strain induced by the lattice mismatch, lattice distortion, or film thickness can strongly alter the physical properties of thin films. Thus, it is necessary to understand the possible effects of the interface strain.…”

Anomalous redox properties and ultrafast chemical sensing behavior of double perovskite CaBaCo2O5+δ thin films

“…The (00l ) peaks of CBCO are all located to the left of corresponding peaks of LAO. According to Bragg equation, the asgrown CBCO thin film has larger lattice parameter than that of LBCO which has lattice-matched parameter [11], although Ca has an even smaller ionic radius of 0.100 nm compared with La of which the ionic radius is 0.103 nm, which is probably resulted from the plenty oxygen vacancy in the two divalent alkaline earth metal ions in the system. The temperature dependence of the electrical resistivity for the CBCO thin film under the oxygen from 300 K to 970 K was studied.…”