The Electrical Conductance of \hbox{SrFeO}_{2.5\,+\,x} Thin Films

Authors: Tunney J.J.; Post M.L.

Source: Journal of Electroceramics, Volume 5, Number 1, August 2000 , pp. 63-69(7)

Publisher: Springer

Abstract:

Thin films of the non-stoichiometric perovskite \hbox{SrFeO}_{2.5 \,+\, x} have been grown by the pulsed excimer laser deposition technique onto sapphire substrates. The electrical conductance properties of the thin films have been determined in a series of experiments done both isothermally and with programmed temperature changes from ambient to 490°C and under \hbox{O}_{2}/\hbox{N}_{2} atmospheres with oxygen concentrations in the range from 100 ppm to 100%. Over these ranges of temperature and oxygen partial pressure a wide range of oxygen stoichiometry in \hbox{SrFeO}_{2.5 \,+\, x} occurs (approximately 0 \lt x \lt 0.5), which includes all four known phases in the \hbox{SrFeO}_{2.5 \,+\, x} + \hbox{O}_{2} system. The experimentally measured values for the activation energy of conduction, \varepsilon_{\rm A}, for \hbox{SrFeO}_{2.5 \,+\, x} films at temperatures 100 \lt T \lt 200^\circ\hbox{C} are in the range 0.30 \lt \varepsilon_{\rm A} \lt 0.47\,\hbox{eV} under oxygen at partial pressures 0.001 \lt P_(O\vskip2\scale70%{2}) \lt 0.05 atm and 0.18 \lt \varepsilon_{\rm A} \lt 0.28\,\hbox{eV} for 0.2 \lt P_(O$\backslash vskip2\backslash scale70\%\{2\})\; \backslash lt\; 1\; atm.\; These\; values\; for\; \backslash varepsilon\_\{\backslash rm\; A\}\; are\; typical\; for\; compositions\; of\; \backslash hbox\{SrFeO\}\_\{2.5\; \backslash ,+\backslash ,\; x\}\; with\; stoichiometries\; in\; the\; range\; 0.25\; \backslash lt\; x\; \backslash lt\; 0.45.\; For\; T\; \backslash lt\; 300^\{\backslash circ\}\backslash hbox\{C\}\; and\; for\; P\_(O$ \backslash vskip2\backslash scale70\%\{2\})\; \backslash lt\; 0.001\; atm\; the\; films\; were\; essentially\; insulators.\; For\; T\; \backslash gt\; 250^\{\backslash circ\}\backslash hbox\{C\}\; and\; P\_(O$ \backslash vskip2\backslash scale70\%\{2\})\; \backslash gt\; 0.001\; atm,\; the\; oxygen\; stoichiometries\; of\; the\; films\; change\; during\; the\; programmed\; temperature\; ramps.\; For\; these\; conditions,\; the\; values\; \backslash delta\backslash varepsilon\_\{\backslash rm\; A\}/\backslash delta\; T\; exhibit\; minima/maxima\; in\; the\; temperature\; range\; 250\; \backslash lt\; T\; \backslash lt\; 320^\{\backslash circ\}\backslash hbox\{C\}\; which\; are\; interpreted\; as\; being\; due\; to\; the\; onset\; of\; the\; order-disorder\; phase\; transition\; from\; the\; cubic\; to\; the\; tetragonal\; and\; orthorhombic\; ordered\; phases\; of\; \backslash hbox\{SrFeO\}\_\{2.5\; \backslash ,+\backslash ,\; x\}\; with\; oxygen\; stoichiometry\; in\; the\; range\; 0.08\; \backslash lt\; x\; \backslash lt\; 0.38.\; The\; \backslash hbox\{SrFeO\}\_\{2.5\; \backslash ,+\backslash ,\; x\}\; thin\; films\; have\; application\; as\; oxygen\; sensing\; materials,\; and\; a\; relationship\; between\; conductance\; and\; oxygen\; sensitivity,\; S\_\{ox\},\; has\; been\; derived.\; The\; values\; of\; S\_\{ox\}\; for\; \backslash hbox\{SrFeO\}\_\{2.5\; \backslash ,+\backslash ,\; x\}\; thin\; films\; increases\; by\; more\; than\; an\; order\; of\; magnitude\; for\; compositions\; close\; to\; the\; lower\; stoichiometric\; limit\; where\; the\; principal\; phase\; conversion\; is\; between\; the\; cubic\; perovskite\; and\; the\; brownmillerite\; forms.$$$

Keywords: perovskite; brownmillerite; SrFeO; thin film; oxygen sensor

Language: English

Document Type: Regular paper

Affiliations: 1: Institute for Chemical Process and Environmental Technology, National Research Council of Canada, Montreal Road, Ottawa, Ontario, K1A 0R6, Canada

Publication date: 2000-08-01

• In this: publication
• By this: publisher
• In this Subject: Electrical & Nuclear Engineering ,  General & Civil Engineering
• By this author: Tunney J.J. ;  Post M.L.

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