Crystal Structure Analysis of Hydrothermally Synthesized Epitaxial (K_xNa_1-x)NbO₃ Films

Abstract

Epitaxial (K x Na1-x )NbO3 films with various compositions x were deposited on Nb-doped (100)SrTiO3 single crystal substrates at 240 °C by the hydrothermal method. Detailed crystal structures were analyzed by X-ray diffraction. All the (K x Na1-x )NbO3 films consisted of a perovskite phase without any impurity phase. High-temperature XRD data showed that (K x Na1-x )NbO3 films with x = 0.03 and 0.86 transformed to a single cubic phase at 600 °C through the intermediate phase. On the other hand, (K x Na1-x )NbO3 films with x = 0.24 showed two diffraction peaks at 600 °C originating from individual phases having different unit cell volumes. The result shows that these films consisted of a mixture of two perovskite phases with K- and Na- rich (K x Na1-x )NbO3 composition.

Deposition of orientation-controlled thick (K,Na)NbO₃ films on metal substrates by repeated hydrothermal deposition technique

“…It was confirmed on our previous work that the composition is a similar value to K/(K + Na) of 0.86, for which we had demonstrated high temperature XRD. 16) According to this study, the multiple peaks at room temperature merged into a single peak by phase transition to cubic phase above 500°C, indicating the single phase without phase separation. On the other hand, a film with K/(K + Na) of 0.24 showed two peaks even at high temperature, indicating phase coexistence.…”

“…13) In addition, this composition was suitable for the energy harvest applications due to its relatively large piezoelectric response and low dielectric constant among the hydrothermally deposited films. 16) In addition, there is no phase separation for (K 0.88 Na 0.12 )NbO 3 films that are different from the twophase coexistence films between (K 0.75 Na 0.25 )NbO 3 and (K 0.36 Na 0.64 )NbO 3 . 17) The metal substrate used in this work was Ni-based alloy with a 300-¯m thick (Inconel 600, hereafter denoted as "Inconel") because Inconel has high thermal stability and resistance to chemical solutions.…”

“…21) The orthorhombic crystal structure has already confirmed by the high-temperature XRD for the (K 0.86 Na 0.14 )NbO 3 film deposited by hydrothermal technique, where the successive phase transitions with temperature were observed. 16) In addition, the Raman scattering spectroscopy showed orthorhombic phase even for thick films prepared by the numbers of deposition cycles. Thus, the present (K 0.88 Na 0.12 )NbO 3 is expected to have the orthorhombic structure.…”

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

“…Deposition temperature (T depo. ) and temperature of the phase transition from orthorhombic to tetragonal (T o-t ) and tetragonal to cubic (T C ) obtained from high-temperature XRD 29) are also shown. The self-polarized state was maintained regardless of the phase transition between the orthorhombic and tetragonal phases.…”

“…These data obviously show that the poling situation changes below 300 °C and above 500 °C heat treatment, and the film heattreated at 400 °C is at the intermediate situation. Considering that Curie temperature (T C ) of each film is 450 °C, 29,30) this behavior is considered to be related to T C . The difference in e 31,f between the as-prepared and heat-treated films at 600 °C was considered as the difference in the domain boundary contribution.…”