Domain structure and phase transitions in epitaxial KNbO3thin films studied byinsitusecond harmonic generation measurements

摘要

Epitaxial thin films of KNbO3thinsp;were deposited on SrTiO3(100) substrate by laser ablation. In the orthorhombic phase, the four possible domain variants in the KNbO3(110) film growth plane were determined to be KNbO3lsqb;11macr;0rsqb;par;SrTiO3lsqb;001rsqb;, lsqb;001macr;rsqb;, lsqb;010rsqb;, and lsqb;01macr;0rsqb; denoted as X+, Xminus;, Y+, and Yminus;, respectively. Using a fundamental beam of 1064 nm transmitted normal to the film, the second harmonic generation (SHG) signal at 532 nm was measured and correlated to the area fractionsAX+,AXminus;,AY+, andAYminus;of the four domain variantsX+,Xminus;,Y+, andYminus;, respectively, in the growth plane of the film. At room temperature, the area fractions dgr;Ax=AX+minus;AXminus;and dgr;Ay=AY+minus;AYminus;were determined to be sim;3.3percnt; and sim;2.2percnt;, respectively.Inhyphen;situSHG measurements revealed the phase transitions to be 210plusmn;10thinsp;deg;C for orthorhombicndash;tetragonal and 450plusmn;10thinsp;deg;C for tetragonalndash;cubic transitions. In the tetragonal phase (between 210thinsp;deg;C and 450thinsp;deg;C) the KNbO3lang;100rang;par;SrTiOthinsp;3lang;100rang;. The use of SHG as a sensitive, nonhyphen;destructive and realhyphen;time probe of phase transitions and evolution of domains in ferroelectric thin films is demonstrated. copy;1996 American Institute of Physics.