Achieving a high dielectric tunability in strain-engineered tetragonal K0.5Na0.5NbO3 films

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 ($$P_0^f$$ P 0 f ) and the small-field relative dielectric permittivity ($$\chi _0^f$$ χ 0 f ), 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 (K0.5,Na0.5)NbO3 film. This strain-stabilized tetragonal phase is verified by density functional theory (DFT) calculations. (K0.5,Na0.5)NbO3 films based on this design were successfully prepared via a sputtering deposition process on SrRuO3-buffered (100)SrTiO3 substrates. The resulted epitaxial films showed a sizable $$P_0^f$$ P 0 f (~0.21C m−2) and a large $$\chi _0^f$$ χ 0 f (~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.

Thickness-Dependent Domain Relaxation Dynamics Study in Epitaxial K0.5Na0.5NbO3 Ferroelectric Thin Films

“…Therefore, the single-component spectrum of K suggests the absence of any mixed oxidation states in the film. Similarly, the spin–orbital pair of Nb 3d 3/2 (210.37 eV) and Nb 3d 5/2 (207.55 eV) is shown in Figure c, which confirms the presence of only Nb 5+ valence state in the film . However, the O 1s core-level spectrum shows asymmetry, which decomposed into two characteristic peaks.…”

“…Similarly, the spin−orbital pair of Nb 3d 3/2 (210.37 eV) and Nb 3d 5/2 (207.55 eV) is shown in Figure 2c, which confirms the presence of only Nb 5+ valence state in the film. 33 However, the O 1s core-level spectrum shows asymmetry, which decomposed into two characteristic peaks. The intense peak at lower binding energy (530.45 eV) corresponds to lattice oxygen (O L ), and the small peak at 532.59 eV is associated with oxygen vacancies (O V ).…”

Nb2O5, LiNbO3, and (Na, K)NbO3 Thin Films from High-Concentration Aqueous Nb-Polyoxometalates

“…Reduction of these elements in XPS surveys of KNN has been noted before being attributed to evaporation during annealing. 89,91 We did not observe the formation of typical impure phases, so we did not explore using slightly higher stoichiometric ratios of K and Na to compensate for differential evaporation, as previously reported. 54 Nonetheless, controlling the K/Na/Nb ratio in the precursor solution is easily accomplished by varying the amount of sodium and potassium carbonate, and this is carried out without significantly impacting the Nb-speciation or pH.…”

Ferroelectricity and Piezoelectric Response of (Sc,Y)N/(Al,Ga,In)N Monolayer Alternating Stacked Structures by First‐Principles Calculations

“…The epitaxial biaxial strain plays an important role for the properties of ferroelectric thin films. [ 8,36–40 ] The compressive strain enhances the polarization P c of w ‐Y 0.5 In 0.5 N, while the tensile strain induces the decrease of that, which is relative to the lattice parameter ratios c/a change under strain. of In and N In increase 5.7% and 4.4% under 2% strain, respectively.…”