Ferroelectric properties of KTa0.65Nb0.35O3single crystals

Dielectric and Structural Properties of (100) KTa1−xNbxO3 Films Grown on MgO, LaAIO3 and SrTiO3 Substrates by Pulsed Laser Deposition

KTa1−xNbxO3 (KTN) thin films (-6000 Å) were grown on (100) MgO, (100) LaAlO3 (LAO), and (100) SrTiO3(STO) substrates by pulsed laser deposition (PLD). Deposited films were smooth, single phase and exclusively (100) oriented. KTN films deposited on MgO and LAO substrates were easily cracked after deposition or post deposition heat treatment. The film deformation appeared to be caused by strain due to the lattice mismatch between the film and the substrate. A thin buffer layer of ∼100 Å was used to eliminate the cracking problem. The high volatility of K at the film deposition temperature required excess K to be added to the ablation target. Sintering of the target and post-deposition annealing of the films were done in a sealed Pt coated stainless steel container. Rutherford backscattering showed the films to have a 1 to 1 atomic ratio of K to Ta + Nb. On top of the KTN films, Ag interdigitated capacitors were deposited. Room temperature measurements of capacitance and dielectric loss as a function of bias electric field (0 -80 kV/cm) at 1 to 20 GHz were made. Capacitance and dielectric loss measurements were made as a function of temperature and bias electric field at one MHz and as a function of temperature and frequency at 0V DC bias. The results show the strong potential of KTN for use in frequency agile microwave electronics.

Fixing of photorefractive volume holograms in K(1-y)Li(y)Ta(1-x)O(3)

We report the fixing of photorefractive holographic gratings with high efficiency in a sample of K(1-y)Li(y)Ta(1-x)Nb(x)O(3) doped with Cu, V, and Ti. Holograms are thermally fixed through the screening of a photorefractive space-charge f ield by a nonphotoactive species at elevated temperatures. Fixed holograms are revealed by illumination at lower temperatures. Diffraction efficiencies of 25% in a 0.54-cm-thick sample are measured. Holograms undergo thermal decay with a 0.67-eV activation energy.