Effect of Solution Conditions on the Properties of Sol–Gel Derived Potassium Sodium Niobate Thin Films on Platinized Sapphire Substrates

Abstract

If piezoelectric micro-devices based on K0.5Na0.5NbO3 (KNN) thin films are to achieve commercialization, it is critical to optimize the films’ performance using low-cost scalable processing conditions. Here, sol–gel derived KNN thin films are deposited using 0.2 and 0.4 M precursor solutions with 5% solely potassium excess and 20% alkali (both potassium and sodium) excess on platinized sapphire substrates with reduced thermal expansion mismatch in relation to KNN. Being then rapid thermal annealed at 750 °C for 5 min, the films revealed an identical thickness of ~340 nm but different properties. An average grain size of ~100 nm and nearly stoichiometric KNN films are obtained when using 5% potassium excess solution, while 20% alkali excess solutions give the grain size of 500–600 nm and (Na + K)/Nb ratio of 1.07–1.08 in the prepared films. Moreover, the 5% potassium excess solution films have a perovskite structure without clear preferential orientation, whereas a (100) texture appears for 20% alkali excess solutions, being particularly strong for the 0.4 M solution concentration. As a result of the grain size and (100) texturing competition, the highest room-temperature dielectric permittivity and lowest dissipation factor measured in the parallel-plate-capacitor geometry were obtained for KNN films using 0.2 M precursor solutions with 20% alkali excess. These films were also shown to possess more quadratic-like and less coercive local piezoelectric loops, compared to those from 5% potassium excess solution. Furthermore, KNN films with large (100)-textured grains prepared from 0.4 M precursor solution with 20% alkali excess were found to possess superior local piezoresponse attributed to multiscale domain microstructures.

The Role of Particle Contact in Densification of FLASH Sintered Potassium Sodium Niobate

“…FLASH XRD pattern has less defined maxima and an inversion of the relative intensities of the first and second reflections (2 θ ≈ 22.5° and ≈ 32°). This inversion indicates preferential grain orientation in (011) and (100), as observed in KNN thin films and is possibly related to the high degree of shrinkage anisotropy in C.H.R. FLASH.…”

Particle Characteristics’ Influence on FLASH Sintering of Potassium Sodium Niobate: A Relationship with Conduction Mechanisms

“…This may explain the presence of Nb-rich secondary phases, which is deleterious from the application point of view [ 21 ]. In addition, a previously described inversion on the intensity of the first and second XRD reflections occurs for 99.9% BM [ 7 ], that might be associated with some degree of preferential orientation of KNN grains, as reported to occur in KNN thin films [ 22 ].…”

Piezoelectric BiFeO3 Thin Films: Optimization of MOCVD Process on Si

“…The possibility of combining the above-mentioned properties in a single device, a hybrid energy harvester, makes BiFeO 3 one of the most promising materials for the next generation of lead-free harvesters. For piezoelectric harvester, Pb(Zr x Ti 1-x )O 3 (PZT) has been commonly used [6,7], but the rising of environmental issues and questions on process sustainability has brought the light on lead-free perovskites, such as BiFeO 3 , LiNbO 3 [8,9], and (K,Na)NbO 3 [10], because of their encouraging capabilities for hybrid energy harvesting [11][12][13].…”