1. STAR 2015
2. Ferroelectricity in KBNNO
Ferroelectric materials—materials with a spontaneous, switchable polarization when below their Curie temperature—have wide applications ranging from non-volatile memories to piezoelectric sensors. Recently, ferroelectric semiconductors have attracted considerable attention as an alternative to conventional semiconductor materials for photovoltaic solar energy conversion.
One particularly promising class of ferroelectric, photovoltaic semiconductors is the single-phase solid-solution oxide: (1-x)[KNbO3]-x[BaNi0.5Nb0.5 O3- δ] (KBNNO). In the x = 0.1 composition, KBNNO has been reported to have exceptional photovoltaic and ferroelectric properties. An important property of ferroelectric materials is the Curie temperature, the maximum temperature at which ferroelectric materials retain their spontaneous polarization. Here, the ferroelectric phase transitions of the x = 0 and x = 0.1 KBNNO compositions are identified with Raman spectroscopy. Raman spectroscopy uses Raman scattering, inelastic scattering where incident photon energy is shifted by lattice and molecular vibrational states in a material, to directly probe the lattice structure of a crystal. Because the ferroelectric transition is driven by a lattice structure change, Raman spectroscopy can be used to identify the Curie temperature.
From these studies, we have identified the Curie temperature of the x = 0, or un-doped, composition as ~450 C. Remarkably, the x = 0.1 composition shows a Curie temperature of ~230 C.
2. Ferroelectricity in KBNNO
Ferroelectric materials—materials with a spontaneous, switchable polarization when below their Curie temperature—have wide applications ranging from non-volatile memories to piezoelectric sensors. Recently, ferroelectric semiconductors have attracted considerable attention as an alternative to conventional semiconductor materials for photovoltaic solar energy conversion.
One particularly promising class of ferroelectric, photovoltaic semiconductors is the single-phase solid-solution oxide: (1-x)[KNbO3]-x[BaNi0.5Nb0.5 O3- δ] (KBNNO). In the x = 0.1 composition, KBNNO has been reported to have exceptional photovoltaic and ferroelectric properties. An important property of ferroelectric materials is the Curie temperature, the maximum temperature at which ferroelectric materials retain their spontaneous polarization. Here, the ferroelectric phase transitions of the x = 0 and x = 0.1 KBNNO compositions are identified with Raman spectroscopy. Raman spectroscopy uses Raman scattering, inelastic scattering where incident photon energy is shifted by lattice and molecular vibrational states in a material, to directly probe the lattice structure of a crystal. Because the ferroelectric transition is driven by a lattice structure change, Raman spectroscopy can be used to identify the Curie temperature.
From these studies, we have identified the Curie temperature of the x = 0, or un-doped, composition as ~450 C. Remarkably, the x = 0.1 composition shows a Curie temperature of ~230 C.