Tunable Electronic Structure and Surface Defects in Chromium-Doped Colloidal SrTiO_3−δ Nanocrystals

Abstract

Materials. Oleic acid (90%, Fisher Chemical), titanium(IV) bis(ammonium lactate)dihydroxide (TiALH, 50% wt in water * , Alfa Aesar), Sr(OH) 2 •8H 2 O (99%, Alfa Aesar), Cr(NO 3 ) 3 •9H 2 O (Crystalline Certified, Fisher Chemical), tetramethylammonium hydroxide (10 M NMe 4 OH, Acros Organics), hydrazine hydrate (N 2 H 4 •H 2 O, 99%, Acros Organics), ethanol (200 proof, PHARMCO-AAPER) and hexanes (optima, Fisher Chemical) were used as received. Synthesis of colloidal SrTiO 3−δ and Cr 3+ -doped SrTiO 3−δ nanocrystals. Colloidal SrTiO 3 NCs were prepared by a modified hydrothermal method. 1-3 In a typical synthesis, 1.25 mmol of titanium(IV) bis(ammonium lactate)dihydroxide and Sr(OH) 2 •8H 2 O were dissolved in 30 mL of distilled H 2 O. The pH was adjusted to 12.1 with NMe 4 OH (10 M). The solution was transferred to a 45-mL Teflon-lined autoclave and N 2 H 4 •H 2 O (5 mmol) and oleic acid (2.5 mmol) were added. 2 The autoclaves were sealed and heated to 200 °C for 24 h. The resulting oleic acid functionalized NCs were washed with ethanol and suspended in hexanes. The synthetic * The batch of TiALH received from Alfa Aesar contains common impurities of TiO 2 at ~14% and pH of the solution ~8.4-8.5. The presence of insoluble TiO 2 indicates that slow hydrolysis is taking place in the TiALH bottle and definitely overestimates [Ti] in the calculation of x nom =[Cr]/([Cr]+[Ti]).

Enhancement of the SrTiO3 Surface Reactivity by Exposure to Electric Fields

“…Besides a weak signal at g =1.974 attributable to Ti 3+ species (or, more descriptively, Ti 3+ −V O −Ti 4+ , i. e. an electron captured at the oxygen vacancy in the perovskite structure which is delocalized between two Ti 4+ cations), the presence of small Mn 2+ defects (signals labeled with *) is noticed with g ‐value and hyperfine constant of 2.0036 and 85 G, respectively. These impurities usually detectable in even in pure SrTiO 3 systems derive from manganese substitution for titanium ions and could explain the higher concentration of O − species in FS_300.…”

On the formation of superoxide radicals on colloidal ATiO3 (A = Sr and Ba) nanocrystal surfaces

“…We recently reported the synthesis 29 of colloidal SrTiO 3 NCs by modied hydrothermal methods 15,17,18 that are readily suspended in non-polar solvents. Electron paramagnetic resonance (EPR) and optical spectroscopies showed that the SrTiO 3 NCs can display spectroscopic signatures that were assigned to an oxygen-related surface defect that is sensitive to the presence of hydrazine hydrate during synthesis.…”

Controlled processing of polymer nanoribbons: Enabling microhelix transformations

“…These substrates were immediately used for measuring dynamic contact angle or flow coating. The colloidal undoped SrTiO 3 (STO) nanocrystals with oleic acid capping ligands were synthesized using a modified hydrothermal method (average edge dimensions of ~10 nm ± 2 nm) . The STO solutions were kindly provided to us by Kittilstved Research Group, Department of Chemistry, University of Massachusetts Amherst.…”