Identification of $A$- and $B$-Site Cation Vacancy Defects in Perovskite Oxide Thin Films

Cation vacancies on both sublattices ($V_{\mathrm{Ti}}$, $V_{\mathrm{Sr}}$) have been identified in homoepitaxial pulsed laser deposited ${\mathrm{SrTiO}}_3$ films using high intensity variable energy positron annihilation lifetime spectroscopy (PALS) measurements. Film nonstoichiometry was varied by varying laser fluence. PALS showed that on increasing the fluence above the $\mathrm{Ti}/\mathrm{Sr}\sim 1$ value, the concentration ratio $[V_{\mathrm{Sr}}]/[V_{\mathrm{Ti}}]$ systematically increased. Reducing the fluence into the Ti-poor region below resulted in additional vacancy cluster defect formation. Vacancy concentrations greater than $\sim 50\mathrm{ppm}$ were observed in all films.

Figure 1

(a) The ${\mathrm{SrTiO}}_3$ film $c$-axis parameter expansion derived from XRD $2\theta \mathrm{\text{−}}\omega$ scans of the (002) peak (square symbols) and the mean positron lifetime (triangle) (1–5 keV implantation range average), as a function of PLD laser fluence. (b) The component positron lifetimes and (c) intensities for the $1.50–2.00\mathrm{J}{\mathrm{cm}}^{-2}$ films (3–5 keV average). The $V_{\mathrm{Ti}}$ and $V_{\mathrm{Sr}}$ lifetimes, 181 and 281 ps, respectively, are shown in (b).

Figure 2

Depth profiled positron lifetime components for the $1.67\mathrm{J}{\mathrm{cm}}^{-2}$ ${\mathrm{SrTiO}}_3$ film. (a) Lifetimes (dashed lines denote 181 and 281 ps), (b) intensities with positron implantation energy. The dashed lines denote the 3–5 keV (gray shading) average values. (c) The Makhovian positron implantation profiles [substrate denoted by gray (yellow) shading].