Achieving a high dielectric tunability in strain-engineered tetragonal K0.5Na0.5NbO3 films
Lanxia Hao, Yali Yang, Yu Huan, Hongbo Cheng, Yuyao Zhao, Yingying Wang, Jing Yan, Wei Ren, Jun Ouyang
Abstract
Abstract Using a modified Landau-Devonshire type thermodynamic potential, we show that dielectric tunability η of a tetragonal ferroelectric film can be analytically solved. At a given electric field E , η is a function of the remnant polarization ( $$P_0^f$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ) and the small-field relative dielectric permittivity ( $$\chi _0^f$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>χ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ), which are commonly measured material properties. After a survey of materials, a large η ~80% is predicted to be achievable in a (001)-oriented tetragonal (K 0.5 ,Na 0.5 )NbO 3 film. This strain-stabilized tetragonal phase is verified by density functional theory (DFT) calculations. (K 0.5 ,Na 0.5 )NbO 3 films based on this design were successfully prepared via a sputtering deposition process on SrRuO 3 -buffered (100)SrTiO 3 substrates. The resulted epitaxial films showed a sizable $$P_0^f$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> (~0.21C m −2 ) and a large $$\chi _0^f$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>χ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> (~830–860), as well as a large η close to the theoretical value. The measured dielectric tunabilities as functions of E are well described by the theoretical η ( E ) curves, validating our integrated approach rooted in a theoretical understanding.