Photorefractive effects and photocurrents in KNbO3: Fe

Abstract

Holographic measurements of optically induced refractive index changes (light damage) of Fe doped KNb03 are interpreted in terms of photoconductivity results. In "undoped" KNb03 the light damage is one order of magnitude smaller than in LiNbO3.The light induced index changes can be drasticaUy reduced or enhanced by applying a relatively small dc-field along the polar f c axis. The space-charge field due to the "photovoltaic effect" is then increased or decreased by photoconductivity.The spatial frequency dependence of the light-induced index changes indicates, that diffusion processes of charge carriers are important for the light damage in KNb03 if the fringe spacing A of the recorded hologram is smaller than 2 pm. For A = 0.35 pm this term is two orders of magnitude larger thanjthe "photovoltaic effect" and the photoconductivity term.The dispersion of the absorption-and photoinduced currentdensity measurements yield basic information on the energy levels of the photorefractive centers controlling the index damage.

Hydrothermal synthesis of KNbO3 and NaNbO3 powders

“…NaNbO 3 is antiferroelectric at room temperature. This lack of spontaneous polarization at room temperature accounts for the comparatively lower interest in NaNbO 3 than in KNbO 3 . NaNbO 3 does, however, form a solid solution with KNbO 3 that is ferroelectric at room temperature and has recently attracted attention as a promising component for nonvolatile memory devices, actuators, and microsensors.…”

“…Komarneni and co-workers 8 reported that KNbO 3 could be synthesized at 194°C by reacting Nb 2 O 5 in a solution containing 3 M OH − and 9 M K + while Uchida et al 10 reported using 3 M KOH at 250°C. Lu et al obtained orthorhombic KNbO 3 (the stable form) by reacting Nb 2 O 5 with 8 M KOH at 200°C and observed that the crystal structure became cubic with increasing niobium concentration in the solution. 9 Both Komarneni et al 8 and Lu et al 9 noticed large variations in the amount of powder recovered for different KOH concentrations.…”

“…7 In contrast, crystalline KNbO 3 powders can be synthesized by the hydrothermal method at temperatures below 200°C. 8,9 Unlike BaTiO 3 , the hydrothermal synthesis of KNbO 3 powders has not been extensively investigated. Komarneni and co-workers 8 reported that KNbO 3 could be synthesized at 194°C by reacting Nb 2 O 5 in a solution containing 3 M OH − and 9 M K + while Uchida et al 10 reported using 3 M KOH at 250°C.…”

“…[1][2][3] In conventional, solid-state synthesis of KNbO 3 using mixed powders, prolonged heating at a high temperature (820°C) is required. 4 More recently, KNbO 3 has been synthesized by the sol-gel method in which alkoxide precursors are used to produce an amorphous gel that is calcined at 600°C to remove the organic components of the gel and to yield crystalline KNbO 3 .…”

“…NaNbO 3 does, however, form a solid solution with KNbO 3 that is ferroelectric at room temperature and has recently attracted attention as a promising component for nonvolatile memory devices, actuators, and microsensors. 11,12 Although NaNbO 3 powders are also synthesized in this study, the main focus is on hydrothermally synthesized KNbO 3 . One issue addressed is the variation in the amount of reaction products often recovered in the hydrothermal synthesis of KNbO 3 powder, as mentioned earlier.…”