Hydrothermal synthesis of ferroelectric mixed potassium niobate-lead titanate nanoparticles

Potassium niobate-lead titanate solid-solution nanoparticles have been synthesized using a new hydrothermal method. The key step is an in situ acid-base exothermic reaction with a large excess of KOH, generating an amorphous precipitated gel. This gel, when crystallized in an autoclave for 2 h at 190°C, produces a mixed perovskite solid solution with [KNbO ₃]_0.8-[PbTiO₃]_0.2 (KNPT) composition, and parallelepiped particles rang in size from a few tens to a few hundreds of nanometer in length. This study proves that the pure perovskite phase can be obtained in spite of the different solubilities of the reactive cations in an ethanol-water solution. Dielectric measurements show that KNPT ceramic with a grain size of 50 nm is ferroelectric at room temperature. In addition, ceramics sintered at 950°C have an average grain size of 500 nm, and exhibit a maximum permittivity of 2100 at 1 kHz near T_C = 510 K and a remanent polarization P_r = 12 μC/cm²