Volatilization of alkali ions and effects of molecular weight of polyvinylpyrrolidone introduced in solution-derived ferroelectric K_0.5Na_0.5NbO₃ films

Abstract

Ferroelectric K0.5Na0.5NbO3 (KNN) thin films were prepared by a chemical solution deposition approach with polyvinylpyrrolidone (PVP) of different molecular weights introduced in the precursor solutions. The volatilization of the alkali ions and the effects of the molecular weight of PVP were examined with x-ray diffraction (XRD), thermal analysis, mass spectrometry, and x-ray photoelectron spectroscopy (XPS). The results clearly showed that the volatilization of the alkali ions mainly happened at moderate temperatures before the crystallization of the KNN perovskite phase. Loss of Na was more significant than K ions during the heating process of KNN. The introduction of PVP with the appropriate molecular weight could effectively promote the crystallization of the KNN perovskite phase at reduced temperature and substantially suppress the loss of the alkali ions before crystallization. Therefore, a high dielectric constant, piezoelectric coefficient, and well saturated ferroelectric hysteresis loops were obtained in the KNN films in which PVP of the right molecular weight were introduced.

Enhanced ferroelectric properties in Mn-doped K0.5Na0.5NbO3 thin films derived from chemical solution deposition

“…[4][5][6][7] Although the KNN thick films with improved performances were prepared by polyvinylpyrrolidone ͑PVP͒modified CSD method in our previous work, [8][9][10][11] the KNN films with thickness less than 2 m still cannot show well saturated ferroelectric hysteresis loops. 1-3 Thin films of KNN can be used for integrated sensors and transducers, as well as piezoelectric microelectromechanical system devices.…”

“…[8][9][10][11] For Mndoped KNN precursor solution, manganese acetate was introduced before niobium ethoxide was added in the solution. [8][9][10][11] For Mndoped KNN precursor solution, manganese acetate was introduced before niobium ethoxide was added in the solution.…”

Structure and electrical properties of Na0.5Bi0.5TiO3ferroelectric thick films derived from a polymer modified sol-gel method

“…The grain nucleation starts from the bottom electrode interface. The decomposition of the PVP polymer during the thermal treatment promotes structural relaxation and prevents cracking in the films [14], [15]; however, some cracks in the films can be observed in the FESEM pictures with larger scales (not shown here). The cracks lead to the increase of the leakage currents and deterioration of the electrical properties.…”

“…PVP with an average molecular weight of 30 000 was added to the precursor solution. The molar ratio of PVP monomer to tetrabutyl titanate is 1:1 in the experiment [3], [14], [15], [17]. The concentration of the precursor solution was adjusted to 0.45 M. The solution was deposited on (111) Pt/TiO 2 /SiO 2 /Si substrates by a spin coating method.…”

“…The sol-gel process has several advantages over other techniques, such as low cost and low annealing temperature to limit volatilization of compositions. Polymers used in a sol-gel process can help to achieve the desired viscosity of precursor solutions and act as binding agents to metal precursors [14], [15]. By proper control and optimization of processing parameters such as sol concentration, spin coating parameters, heat treatment, and repeat times, thick films with desired thickness and minimum defects can be obtained.…”