Sr diffusion in undoped and La-doped SrTiO₃single crystals under oxidizing conditions

Abstract

Strontium titanate SrTiO 3 (100), (110), and (111) single crystals, undoped or donor doped with up to 1 at% La, were isothermally equilibrated at temperatures between 1523 and 1773 K in synthetic air followed by two different methods of Sr tracer deposition: ion implantation of 87 Sr and chemical solution deposition of a thin 86 SrTiO 3 layer. Subsequently, the samples were diffusion annealed under the same conditions as before. The initial and final depth profiles were measured by SIMS. For strong La-doping both tracer deposition methods yield similar Sr diffusion coefficients, whereas for weak doping the tracer seems to be immobile in the case of ion implantation. The Sr diffusivity does not depend on the crystal orientation, but shows strong dependency on the dopant concentration supporting the defect chemical model that under oxidizing conditions the donor is compensated by Sr vacancies. A comparison with literature data on Sr vacancy, Ti, and La diffusion in this system confirms the concept that all cations move via Sr vacancies. Cation diffusion is several orders of magnitude slower than oxygen diffusion.

Sintering and grain growth in SrTiO₃: impact of defects on kinetics

“…15), 16) In the present sintering experiments the diffusion coefficients are higher by two orders of magnitude at the same temperature. However, higher diffusion coefficients in sintering experiments compared to tracer data are well-known; 40),44), 45) this is probably attributed to the influence of the microstructure and the difference in the driving force between the experimental setups.…”

“…For grain growth some investigations explained changes in microstructure by the total defect concentration. 41),42) While these studies focus on oxygen vacancies, we propose strontium vacancies as dominant defect species for diffusion, densification and grain growth as proposed by Goemann et al 15), 16) We also consider the existence of an internal space charge layer at the grain boundaries 17),18),23), 43) to explain some of our findings.…”

“…Impedance data, 25) SIMS (Secondary ion mass spectrometry) measurements 10) and simulations 5) provide detailed data of the space charge properties. The typical width of the space charge region ranges from several nanometers up to 100 nm and the potential at the grain boundary is commonly determined as 0.4 1.0 V. A set of diffusion data for Ti and Sr in SrTiO 3 single crystals is presented by Goemann et al, 15), 16) which indicates that both species diffuse via strontium vacancies at high temperature. Data for strontium vacancy mobilities are presented by Poignant and Juda 26) for polycrystalline (Sr,Ca)(Ti,Nb)O 3 and Meyer et al 27) for single crystalline SrTiO 3 .…”

134Ba diffusion in polycrystalline BaMO3 (M = Ti, Zr, Ce)

“…13 The Ba lattice diffusion in BaMO 3 compared to the A-site cation diffusion in general in perovskites reported in the literature revealed no apparent trend. [26][27][28][29][30][31][32][33][34][35][36][37][38] In addition, the diffusion mechanisms for the data reported in the literature are usually not described. The point defect chemistry after materials processing determines the dominating diffusion mechanism as shown for BaZrO 3 .…”

Dislocations in plastically deformed SrTiO3

“…Diffusion activation enthalpies in the bulk are 1 eV for oxygen and 3.5-4 eV for Sr [11,12]. For Ti no reliable data exist, but it is assumed that the diffusion of Ti is the slowest among the three species [12]. It is important to note that for 'climb dissociation' diffusion is required only between the partials (i.e.…”