Twin structures in tetragonal SrTiO3: The ferroelastic phase transition and the formation of needle domains

Direct optical observation of the twin domains in ferroelastic strontium ti tanite at 8 K < T < 105 K show that twin boundaries in the bulk do not chan ge at temperatures below 103.4 K. At temperatures between 103.4 K and T-c = 105.65 K the contrast between the birefringences of two adjacent domains i s too weak to allow the visual observation of the domain wall. The temperat ure independent, coarse domain structure in the bulk of the crystal is in s trong contrast with a fine domain structure and strain relaxations near the crystal surface. No indication for wall flip motion was found for repeated , slow cooling, and heating through the transition point. (C) 1999 American Institute of Physics. [S0021-8979(99)01915-5].