Supporting Information. Solution-Based Growth of Monodisperse Cube-Like BaTiO 3 Colloidal Nanocrystals

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1 Supporting Information Solution-Based Growth of Monodisperse Cube-Like BaTiO 3 Colloidal Nanocrystals Shiva Adireddy, Baobao Cao, Cuikun Lin, Weilie Zhou and Gabriel Caruntu* Chemistry Department and the Advanced Materials Research Institute University of New Orleans, New Orleans, Louisiana, gcaruntu@uno.edu 1

2 Chemicals. Barium nitrate (Ba(NO 3 ) 2 ) 99.95`%, sodium hydroxide 98%, 1-butanol anhydrous 99.9%, Titanium (IV) n-butoxide 98+%, oleic acid 99% were purchased from Alfa Aesar and used without any further purification. Synthesis of cube-like BaTiO 3 nanoparticles. In a typical procedure for the preparation of cube-like nanocrystals different solutions, containing 1 mmol of Ba(NO 3 ) 2 dissolved in 5 ml of deionized water, 12.5 mmol of NaOH dissolved in 5 ml of deionized water, 1 mmol of Ti(Bu) 4 dissolved in 5 ml BuOH and 2.5 ml of oleic acid in 5 ml of BuOH were mixed together and the resulting solution subsequently transferred to a 23 ml Teflon-lined stainless steel autoclave (Parr Instruments). The autoclave was sealed and was subsequently heated to 135 o C for 18 h. After the completion of the reaction the reaction mixture was cooled naturally to room temperature and separated from the supernatant solution by centrifugation. The precipitate was collected, purified and eventually dispersed in toluene yielding a stable milky colloidal solution. Because XRD data has shown that the as-prepared cube-like nanoparticles present a secondary phase, identified as BaCO 3 (10% in weight), but which can be eliminated upon washing of the powder with a diluted (5%) acetic acid solution, another set of experiments were performed in a glove-box. The reaction solution was obtained by mixing the 4 solutions under anaerobic conditions was transferred to a Parr bomb, then the bomb was sealed and treated hydrothermally under the same conditions as the sample prepared in open atmosphere. To demonstrate the feasibility of this method, no size selection was performed to narrow the size distribution of the nanoparticles. The yield of the BaTiO 3 nanoparticles was 85-90%. Characterization. The composition of the nanopowders was investigated by energy dispersive X-Ray spectroscopy (EXAFS) on a JEOL 2010 electron microscope. To characterize the morphology, internal structure and size of the BaTiO 3 nanocrystals analysis by TEM, HRTEM and SAED was performed on a JEOL 2010 at a bias voltage of 200 kv. The surface composition of the BaTiO 3 nanoparticles was studied with a Thermo Nicolet Omnic FT-IR spectrometer in the attenuated total reflection mode. The wavelength range was from 500 to 400 cm -1. Raman spectra at room temperature were collected with a Nicolet Almega XR Dispersive Raman Spectrometer using a 1064 nm excitation of an Nd/YAG laser. The phase structure and purity of the samples were studied by powder X-Ray diffraction (XRD) (Panalytical X Pert system with 2

3 monochromatic Cu K α radiation (l= Å at 40 kv and 40 ma). Diffraction data were collected at room temperature by step scanning in the range 15 o 2θ 75 o Photoluminescence measurements were performed at room temperature on Perkin-Elmer LS55 spectrometer using an excitation source at 275 nm with a 450 W Xe arc lamp with a step size of 0.02 o and a counting time of 20 s at each step. 3

4 Figure S1. Low magnification TEM image of the cube-like BaTiO 3 nanoparticles. The inset represents the size distribution plot obtained by counting 100 nanoparticles. The aspect ratio (l) is defined as the ratio between the longer and the shorter edge, respectively. 4

5 Figure S2. HRTEM image of an individual cube-like nanoparticle (a) and the corresponding fast Fourier transform (FFT) (b); Selected area electron diffraction (SAED) image of the cubelike BaTiO 3 nanoparticles 5

6 Figure S3. Low magnification TEM image of the cubic BaTiO 3 nanoparticles (the inset represents a size distribution plot obtained by counting 100 nanoparticles). 6

7 Figure S4. EDX spectrum of the cubic BaTiO 3 nanoparticles. 7

8 Figure S5. FT-IR spectrua of the 21.5 nm cubic BaTiO 3 nanoparticles (blue line) and oleic acid (red curve). The inset picture shows a colloidal solution of BaTiO 3 nanocubes after 3 months from the preparation 8

9 Weight (mg) Temperature Difference( o C) Temperature ( o C) Figure S6. The TGA/DSC profile of the BaTiO 3 nanopowders. The endothermic peak observed at T=383.8 o C corresponds to the weight loss of 4.41% representing the amount of oleic acid molecules retained on the surface of the nanoparticles 9

10 Figure S7. Schematic diagram of the photoluminescence process in BTO colloidal nanoparticles 10