Hardening of the ferroelectric soft mode in SrTiO3 thin films

We have studied the origin of soft-mode hardening in SrTiO3 thin films using broadband terahertz time-domain spectroscopy. We measured the dielectric dispersions in the terahertz region of as-deposited, O2 annealed, and high-temperature annealed SrTiO3 thin films deposited on MgO and La0.3Sr0.7Al0.65Ta0.35O3 substrates. The results show that the ferroelectric soft mode softens dramatically by the high-temperature annealing. We also measure x-ray diffractions and atomic force microscope images and conclude that the hardening of the ferroelectric soft mode in the thin films is determined by the grain size of each crystalline domain which is enlarged by the high-temperature annealing due to remelting.

[1]  A. Yamanaka,et al.  Evidence for competing orderings in strontium titanate from hyper-Raman scattering spectroscopy , 2000 .

[2]  Masayoshi Tonouchi,et al.  Observation of TO1 soft mode in SrTiO3 films by terahertz time domain spectroscopy , 2005 .

[3]  Shih,et al.  Size dependence of the ferroelectric transition of small BaTiO3 particles: Effect of depolarization. , 1994, Physical review. B, Condensed matter.

[4]  Dwight W. Berreman,et al.  Adjusting Poles and Zeros of Dielectric Dispersion to Fit Reststrahlen of Pr Cl 3 and La Cl 3 , 1968 .

[5]  A. Tagantsev,et al.  Annealing effect on dislocations in SrTiO3∕LaAlO3 heterostructures , 2007 .

[6]  Masayoshi Tonouchi,et al.  Cutting-edge terahertz technology , 2007 .

[7]  M. Jelínek,et al.  Far-infrared spectroscopy of a SrTiO3 thin film , 1998 .

[8]  Martin Dressel,et al.  Origin of soft-mode stiffening and reduced dielectric response in SrTiO3 thin films , 2002 .

[9]  H. Koinuma,et al.  Step-flow growth of SrTiO3 thin films with a dielectric constant exceeding 104 , 1999 .

[10]  P. Kužel,et al.  Infrared and Raman studies of the dead grain-boundary layers in SrTiO3 fine-grain ceramics , 2007 .

[11]  Xicheng Zhang,et al.  Materials for terahertz science and technology , 2002, Nature materials.

[12]  J. Melngailis,et al.  Scaling of ferroelectric and piezoelectric properties in Pt/SrBi2Ta2O9/Pt thin films , 1999 .

[13]  Zhigang Suo,et al.  The effect of stress on the dielectric properties of barium strontium titanate thin films , 1999 .

[14]  K. Abe,et al.  Thickness Dependence of Ferroelectricity in Heteroepitaxial BaTiO3 Thin Film Capacitors , 1999 .

[15]  A. Golnik,et al.  Soft-mode hardening in SrTiO3 thin films , 2000, Nature.

[16]  K. Müller,et al.  SrTi O 3 : An intrinsic quantum paraelectric below 4 K , 1979 .