The Relationship Between Photoluminescence and Short-Range Order Structure in SrTi1-xAlxO3 Amorphous Compounds

Nov 26, 2018 - 7:00 PM -  CM02.03.21
Hynes, Level 1, Hall B
Valmor Mastelaro1,Yajaira D.R. Jerez1,Lauro Maia2,Alain Ibanez3

University of Sao Paulo1,Federal University of Goias2,Institut NÉEL - CNRS3
Although compounds exhibiting the perovskite structure, and particularly SrTiO<sub>3</sub>, have been very well studied concerning their photoluminescence (PL) properties, to our knowledge, the effect of water purity used and the addition of aluminum substituting partially titanium atoms on the PL properties have not yet been studied. To complete the previous studies, samples of SrTi<sub>1-x</sub>Al<sub>x</sub>O<sub>3</sub> composition with x ranging from 0.005, 0.01, 0.03 and 0.05 were prepared by the modified polymer precursor method under different water purity. SrTi<sub>1-x</sub>AlO<sub>3</sub> (STAO) composition samples with the amounts of aluminum equal to x = 0.005, 0.01, 0.03 and 0, 05 were synthesized by the modified polymer precursor method. The obtained resins were subsequently thermally treated at 250 °C at a heating rate of 10 °C/min for 4h under air atmosphere and subsequently ground to obtain fine black amorphous powders. Different temperatures of heat treatments between 450 ~ 500 ° C were selected as well as different calcination times between 2h and 8h. XANES spectra were collected at Ti K-edge using the transmission mode at the XAFS2 beam line of Brazilian storage ring. The pre-edge region of the XANES spectra on the Ti K-edge presents four transitions. They were attributed to a quadrupolar excitation of the 1s electron level to the octahedron t<sub>2g</sub> orbitals; a transition of the 1s electron to unoccupied 3d level; transitions attributed to the dipole excitation of the 1s electron level to the t<sub>2g</sub> and e<sub>g</sub> orbitals of the neighboring octahedron. Significant differences in the intensity of the pre-edge transition for samples containing 3% and 5% of aluminum were observed indicating that in these samples the local symmetry around titanium presents a greater distortion or a greater degree of disorder. This distortion or disorder may originate from the existence of sites with titanium pentacoordinate (<sup>[5]</sup>Ti) or hexacoordinated (<sup>[6]</sup>Ti). The comparison of the intensity of the transition present in the pre-border region of the XANES spectra of the samples versus the value of the PL intensity area, in agreement with literature data, shows a clear evolution of PL emission with the relative proportions / amounts of pentacoordinate and hexacoordinated symmetries and also the PL decreasing with the beginning of the crystallization process.