Growth of epitaxial (K, Na)NbO₃films with various orientations by hydrothermal method and their properties

Abstract

{100}c-, {110}c- and {111}c-oriented epitaxial (K, Na)NbO3 thin films were grown at 240 °C on (100)cSrRuO3//(100)SrTiO3, (110)cSrRuO3//(110)SrTiO3, and (111)cSrRuO3//(111)SrTiO3 substrates by the hydrothermal method. Their film thicknesses increased with the deposition time and then eventually saturated at longer deposition times. Their saturated film thicknesses were mainly determined by their orientation and the order was {100}c-, {110}c- and {111}c-orientation regardless of any experimental conditions. These films consisted of grains with characteristic morphologies. All of the films exhibited similar ferroelectric and piezoelectric properties irrespective of the film orientation. The remnant polarizations (Pr) and coercive fields (Ec) of the {100}c-, {110}c- and {111}c-oriented films at the maximum electric field of 500 kV cm−1 were 31 μC cm−2 and 111 kV cm−1, 27 μC cm−2 and 94 kV cm−1, and 25 μC cm−2 and 110 kV cm−1, respectively, while their effective values of piezoelectric coefficient (d33) were approximately 31–33 pm V−1. Similar films are associated with its mixed domain structure.

High yield preparation of (100)<i>_c</i>-oriented (K,Na)NbO₃ thick films by hydrothermal method using amorphous niobium source

“…3.3 Crystal structure, surface morphology, and electric properties diffraction peaks of orthorhombic 330 and ¹330, and 030 were observed, showing the existence of multi domain structure in the films as we already reported. 28) It must be noted that the intensity ratio of these two peaks was almost the same, suggesting a similar volume fraction of these domains, irrespective of the input mass of the amorphous niobium source. Figures 5(c) and 5(d) show the surface SEM images of films obtained from 2.0 and 0.36 mmol of the amorphous niobium source.…”

“…Figure 2(a) shows the film thickness as a function of input mass of the starting amorphous niobium source for (K 0.88 Na 0.12 )NbO 3 films deposited on (100) c SrRuO 3 // (100)SrTiO 3 substrates for 20 h. It must be noted that the conventional standard input mass of the niobium source was set to be 2.0 mmol. 28) Film thickness increased with increasing input mass of the starting amorphous niobium and reached the maximum value at 0.5 mmol, but the contrary decreased above this value. Figure 2(a) also shows the photographs of collected residual powder after the hydrothermal process.…”

“…The deposition was hardly observed for both cases up to about 2 h because it needs about 2 h to reach the vessel temperature of 240°C. 28) After about 2 h, film thickness almost linearly increased with the deposition time but was saturated at a certain time for both cases. The times when the deposition amount saturated of about 15 h using and 2.0 mmol of niobium sources is almost twice as long as that for 0.2 mmol sources, although the amount of source is ten times larger.…”

Thermal stability of self-polarization in a (K,Na)NbO3 film prepared by the hydrothermal method

“…Polarization switching of all butterfly curves occurs gradually reflecting its orthorhombic crystal symmetry with polar axis along {110} c . 28) The as-prepared and heat-treated films at 300 °C show that the asymmetric butterfly curves shifted to the negative electric field [see Figs. 2(a) and 2(b)], designated as an imprint behavior.…”

Lower-temperature processing of potassium niobate films by microwave-assisted hydrothermal deposition technique

“…We also note that the diffraction peak of (300) could be separated to be 3 components, which means the presence of three different domain structure, probably derived from the symmetry of KN crystal lattice (orthorhombic). 25),28), 30) Figures 3(a) and 3(b) show XRD patterns of the KN films deposited on (100)SRO//STO and (100)STO:Nb substrates, respectively, for lowered reaction temperature of 180220°C for 80 min, using precursor solution of 7 mol dm ¹3 . For the films on both substrates, the peak intensities of (h00) c KN increased with the reaction temperature, meaning the film growth with increasing the temperature.…”