Thermal expansion of the new perovskite substrates DyScO 3 and GdScO 3
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C.D. Brandleb) and A.J. Ven Graitisc) Agere Systems, Murray Hill, New Jersey 07974 (Received 30 June 2004; accepted 12 January 2005)
The thermal expansion coefficients of DyScO3 and GdScO3 were determined from 298 to 1273 K using x-ray diffraction. The average thermal expansion coefficients of DyScO3 and GdScO3 were 8.4 and 10.9 ppm/K, respectively. No phase transitions were detected over this range, though the orthorhombicity decreased with increasing temperature. These thermal expansion coefficients are similar to other oxide perovskites (e.g., BaTiO3 or SrTiO3), making these rare-earth scandates promising substrates for the growth of epitaxial thin films of many oxide perovskites that have similar lattice spacing and thermal expansion coefficients.
I. INTRODUCTION
Rare-earth scandates are of interest as candidate substrates for the epitaxial growth of perovskite and perovskite-related films.1,2 These scandates have pseudocubic lattice constants in the range of 3.93–4.05 Å. This range is devoid of commercially available perovskite substrates suitable for high temperature epitaxial film growth.3 This is of particular importance to the growth of ferroelectric perovskites such as (Ba,Sr)TiO3 and Pb(Zr,Ti)O3 or electron-doped cuprate superconductors like Sr0.9La0.1CuO2.2 An important aspect for the growth of films on these substrates is knowledge of their thermal expansion coefficients. The only rare-earth scandate whose thermal expansion behavior has been reported to date is NdScO3.4 The temperature range however, over which its thermal expansion behavior was reported, 1000 °C to 2000 °C,4 is higher than the typical growth temperatures for perovskite thin films. Rare-earth scandates have the chemical formula ReScO3, where Re is a rare earth element. At room temperature, all ReScO3, with Re ⳱ Ho to La, have the orthorhombic GeFeO3 crystal structure (space group 62Pnma).3–10 Throughout this manuscript we use the standard setting of space group #62, Pnma, to describe the crystallography of DyScO3 and GdScO3. Although some
a)
Address all correspondence to this author. e-mail: [email protected] b) Currently at CrysTex Inc., Basking Ridge, New Jersey. c) Currently at Integrated Photonics, Inc., Hillsborough, New Jersey. DOI: 10.1557/JMR.2005.0126 952
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J. Mater. Res., Vol. 20, No. 4, Apr 2005 Downloaded: 03 Sep 2014
authors use this setting,5,6,12 many others use the nonstandard setting Pbnm to describe the crystallography of DyScO3, GdScO3, and other perovskites with the GdFeO3 crystal structure.1,3,4,7–10 The conversion from axes a ,b, c, directions [a, b, c] or planes (a, b, c) in Pnma to a⬘, b⬘, c⬘, [a⬘, b⬘, c⬘], or (a⬘, b⬘, c⬘) in Pbnm is given by a⬘⳱ c, b⬘⳱ a, and c⬘⳱ b.6 They are isostructural with the commercial perovskite substrate materials NdGaO3 and YAlO3, as well as the conducting perovskite SrRuO3,11 which is commonly used as an epitaxial electrode in epitaxial perovskite thin film heterostructures.8 This structure contains four formula units per unit cell, and hence, four
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