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عنوان فارسی مقاله:
تغییرات در ساختار سطح محلی و کاهش استرانسیوم در کشت آهن استرونتیوم تیتانیت(001)
عنوان انگلیسی مقاله:
Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001)
سال انتشار : 2017
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مقدمه انگلیسی مقاله:
1. Introduction
Strontium titanates among other perovskite oxides have recently attracted significant attention due to their outstanding electrical and ionic transport properties [1,2]. Pure SrTiO3 (or STO) is a wide band semiconductor with an indirect band gap of 3.25 eV and a direct band gap of 3.75 eV with low conductivity. Substitution of Ti by another transition metal, such as Fe, can change the electronic structure and electrical conductivity of the oxide. Various titanates, including SrTi1-xFexO3-, are considered as promising inexpensive alternative to the classical oxygen sensors based on zirconia [1], especially for use in harsh environments. SrTi1-xFexO3- oxides form a family of continuous solid solutions in the range 0 < x < 1 from strontium titanate to strontium ferrate. With variation of x, properties of SrTi1-xFexO3- change from large band gap semiconductor for Ti-rich phase to a conductor for Ferich phase (for x > 0.1) [3,4]. SrTiO3 has cubic perovskite structure. On the other hand, SrFeO3- forms different crystal phases from disordered perovskite SrFeO3 to ordered brownmillerite SrFeO2.5 [5,6]. Mixed compound SrTi1-xFexO3- can retain cubic perovskite structure in wide range of x [6,7]. ∗ CFe in Ti4+ site can acquire two different oxidation states, Fe3+ and Fe4+. The difference in the oxidation state requires oxygen vacancies to be an integral part of the perfect SrTi1-xFexO3- lattice to keep charge neutrality. If one uses the stoichiometry of SrTi1-xFexO3-x/2 [6,8], then half of the Fe3+ can have a mobile oxygen vacancy with an effective positive charge +2 (or V∗∗ O using Kröger–Vink notation [9]). There are three types of coordination around oxygen sites: (i) Fe O Fe; (ii) Ti O Ti; and (iii) Ti O Fe. Iron can be in 4-, 5-, and 6- coordination in SrTi1-xFexO3- with different defect energies of the oxygen vacancies corresponding to these configurations [10]. The Fe3+/Fe4+ ratio will depend on the total Fe concentration x, the oxygen partial pressure p(O2) and the temperature. For x ≈ 0.1–0.3, the electrical resistivity stays almost constant in the p(O2) range of 10−4–1 bar in the temperature range 750–1000 ◦C, which is suitable for oxygen sensor applications [6]. Presence of Fe doping and accompanying oxygen vacancies also enhances surface reactivity of strontium titanate [3,11–13]. The good conductivity, both ionic and electronic, in combination with chemical and structural stability makes Fe-doped STO an attractive material for applications in gas sensors [1,2,14], catalysts [15], fuel cell electrodes [16,17], oxygen permeation membrane [3,18] and resistive switching memory [19–21]. A number of studies have suggested that Fe substitutes Ti due to close ionic radius and valence state. However the substitution of Sr by a dopant transition metal has also been explored. Both experimental and theoretical research on Mn-doped SrTiO3 powders haveindicated that Mn can occupy either Ti(as Mn4+) or Sr site (as Mn2+) depending on the experimental conditions (temperature, oxygen partial pressure and stoichiometry) [22–24]. The calculations performed by Yang et al. [23] have shown that Mn substitution on Ti site is explicitly preferable only in oxygen rich conditions, whereas in oxygen deficit conditions Mn prefers to substitute Sr site. In this work, ion beam implantation was employed for Fe doping of STO single crystals. The method allows us to introduce doping in a controllable way by varying the incident ion energy and concentrations. Here we have chosen Fe implantation doses to result in final Fe concentrations below the solubility level of Fe in the host STO material. For Fe doses above ∼1 × 1017 atoms/cm2, there is a possibility to form metallic Fe nanoparticles inside the host material [25–27]. For instance, Dulov et al. [25] reported the formation of -Fe nanoparticles in SrTiO3 at the implantation dose of 1.5 × 1017 ions/cm2, whereas at the dose of 0.75 × 1017 ions/cm2, they mostly observed formation of SrTi1-xFexO3- phase. Therefore, smaller implantation doses were used in this study to avoid precipitation of iron.
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Changes in local surface structure and Sr depletion in Fe-implanted ... https://www.sparrho.com/...structure-and-sr-depletion-in-fe-implanted-srtio3.../9d5b2... Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001). Imported: 20 Oct '16 | Published: 05 Oct '16. O. Lobacheva, Y.M. Yiu; N. Chen; ... Applied surface science - Terkko Navigator https://www.terkko.helsinki.fi/.../15459059_changes-in-local-surfa... Translate this page Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001). Added 207 days ago (05.10.2016). Journal: Applied surface science. CanadianLightSource on Twitter: "PAPER: Changes in local surface ... https://twitter.com/canlightsource/status/782999966621073408 Oct 3, 2016 - PAPER: Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001) http://ow.ly/4DAt304NPxm. Like 1; أمة الله. 10:45 AM ... Changes in local surface structure and Sr depletion in Fe-implanted ... newscentral.exsees.com/.../7b9cf2b3aa70a8c399cd6059704af4d4-a3acc3fc6a19159f4b... Oct 16, 2016 - ... local surface structure and Sr depletion in Fe-implanted SrTiO3 (001) ... crystal strontium titanate SrTiO 3 (001) samples implanted with Fe in ... Adsorption and Reaction of CO and CO2 on Oxidized and Reduced ... pubs.acs.org/doi/abs/10.1021/jp045864b by S Azad - 2005 - Cited by 38 - Related articles Apr 21, 2005 - Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 ... Adsorption of small molecules at the cobalt-doped SrTiO3(001) ... Nucleation and Growth of Fe Nanoparticles in SiO2: A TEM, XPS, and ... pubs.acs.org/doi/abs/10.1021/jp206357c?mi=t1wjr4&af=R&pageSize=20... Sep 21, 2011 - In this study, the nucleation and growth of iron nanoparticles in the ... in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001). User Services Online - Canadian Light Source uso.lightsource.ca/publications/?o=-0.-2.1&page=127 Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001). Applied Surface Science 393, 74-81. 10.1016/j.apsusc.2016.09.131. SGM ...
