Publication No.1



H. Pinto, A. Stashans, P. Sánchez.
Theoretical studies of impurity-doping in BaTiO3 and SrTiO3 crystals - NATO 
Adv. Workshop Def. Surf. Eff. Adv. Perovskites, Jurmala (Latvia), 1999, p.37. 

Abstract:
There has been a long-term interest in the perovskite-type ceramics because of their 
unusual magnetic and dielectric properties. BaTiO3 finds increasing processibility as 
an active element in micro-electronic devices and as a promising material for self-pumped 
phase conjugation and cheap diode lasers. The typical application of SrTiO3 is its use as 
a grain-boundary barrier layer capacitor because of its low dielectric loss and good 
temperature stability, and as a superconductor at low temperatures. Using the modified 
for crystals INDO method which had shown reliability in a number of applications, the 
authors investigate impurity-bound polarons in BaTiO3 and band structure of La-doped SrTiO3
The geometrical configurations, structural and optical properties of bound-polarons in 
the BaTiO3 cubic lattice have been studied by means of the Large Unit Cell (LUC) model 
incorporated into the relevant computer code CLUSTERD. As a result it was found that the 
polaron finds itself localised on one or two oxygens situated close to  the Al- or Sc-
impurity which substitutes for Ti atom. The calculated absorption energies are compared 
with the available experimental data.
   Using the same LUC model, La-impurity substituting for a Sr atom is studied in the cubic 
lattice of SrTiO3 crystal. By changing the extension of the LUC we compute different 
concentrations of La and study the effect of concentration upon the band structure properties. 
The calculated local energy levels within the band gap are discussed in comparison with the 
experimental results. 




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