Search results for "Potassium"
showing 10 items of 930 documents
Hydrothermal Synthesis of ZnO Crystals from Zn(OH)2 Metastable Phases at Room to Supercritical Conditions
2014
The originality of this work is to highlight the effect of temperature and pressure on the size and morphology of hydrothermal ZnO particles from ambient to supercritical conditions (T > 374 °C and P > 221 bar) using a unique continuous one-step process. Experiments were carried out from zinc nitrate (Zn(NO3)2) and potassium hydroxide (KOH) solutions in the ranges of 1–300 bar and 30–400 °C. The as-prepared particles of ZnO (flower, ellipsoid, and sphere) and e-Zn(OH)2 (polyhedral) sized from nano to micrometers were characterized by X-ray diffraction and electronic microscopy. The wulfingite phase (e-Zn(OH)2) was detected inside some powders especially at room temperature for higher pressu…
Modelling of defects and surfaces in perovskite ferroelectrics
2003
The results of electronic structure calculations for different terminations of SrTiO 3 (100) and (110) perovskite thin films are discussed. These calculations are based on the ab initio Hartree-Fock (HF) method and Density Functional Theory (DFT). Results are compared with previous ab initio plane-wave LDA and classical Shell Model (SM) calculations. Calculated considerable increase of the Ti-O chemical bond covalency nearby the surface is confirmed by experimental data. Our quantum chemical calculations performed by means of the intermediate neglect of differential overlap (INDO) method confirm the existence of self-trapped electrons in KNbO 3 , KTaO 3 and BaTiO 3 crystals. The relevant la…
Transient optical absorption in KNbO3 crystals irradiated with pulsed electron beam
1997
Abstract Transient optical absorption spectra as well as absorption decay kinetics in pure, Mg- and Rb-doped KNbO 3 have been measured at RT after pulsed (10 ns, 0.27 MeV) electron beam irradiation. Three types of short-lived radiation defects are observed with bands peaking at ∼460 nm, ∼780 nm and > 1000nm. The relevant radiation-induced decay processes are discussed.
Semi-empirical defect calculations for the perovskite KNbO3
2000
A new parametrization of the classical shell model for the cubic phase of the perovskite KNbO3 has been derived and used to calculate the structural, elastic and dielectric properties of this material. Using this parametrization, the defect formation and migration energies, as well as atomic displacements, have been calculated. In parallel, the quantum mechanical method of the intermediate neglect of the differential overlap (INDO) has been applied to the same problem. The migration energies for the O vacancy obtained by these quite different methods are reasonably close (0.68 eV and 0.79 eV, respectively) and also agree with the only experimental estimate available of approximately 1 eV. A…
Quantum chemical modelling of point defects in KNbO3 perovskite crystals
2000
Abstract We present results of semi-empirical quantum chemical calculations for several perovskite KNb x Ta 1−x O 3 (KTN) solid solutions, as well as point intrinsic defects – F centers and hole polarons bound to K vacancy – in KNbO 3 . Method of the intermediate neglect of the differential overlap (INDO) was combined with typically 320-atom supercells and atomic geometry optimization. Analysis of the optimized atomic and electronic structure has clearly demonstrated that several nearest Nb atoms substituting for Ta in KTaO 3 – unlike Ta impurities in KNbO 3 – reveal the self-ordering effect, which probably triggers the ferroelectricity observed in KTN. We predict co-existence of one-site (…
Broadband Dielectric Investigation of Sodium Potassium Niobate Ceramic Doped 8% of Antimony
2012
In this work we present dielectric permittivity measurement results of KNN ceramic doped antimony (K0.5Na0.5)(Nb0.92Sb0.08)O3 with sintering aid MnO2 (0.5 mol% MnO2) (KNNSbx + 0.5Mn). Its dielectric properties were investigated in broad frequency (from 20 Hz to 32 GHz) and temperature (from 26 K to 780K) ranges. Above room temperature obtained results show two diffused phase transitions. Below room temperature investigation revealed dielectric permittivity dispersion similar to the relaxor one. The obtained mean relaxation times fulfills Arrhenius relationship with dipole activation energy Ea/kB = 2282 K.
CCDC 1427507: Experimental Crystal Structure Determination
2015
Related Article: Eugenio Coronado, M. Carmen Giménez-López, Tomasz Korzeniak, Georgiy Levchenko, Francisco M. Romero, Alfredo Segura, Valentín García-Baonza, Julio C. Cezar, Frank M. F. de Groot, Alla Milner, Moshe Paz-Pasternak|2008|J.Am.Chem.Soc.|130|15519|doi:10.1021/ja8047046
CCDC 1427488: Experimental Crystal Structure Determination
2015
Related Article: Eugenio Coronado, M. Carmen Giménez-López, Tomasz Korzeniak, Georgiy Levchenko, Francisco M. Romero, Alfredo Segura, Valentín García-Baonza, Julio C. Cezar, Frank M. F. de Groot, Alla Milner, Moshe Paz-Pasternak|2008|J.Am.Chem.Soc.|130|15519|doi:10.1021/ja8047046
Interesting synthetic routes from the reinvestigation of the reaction of the M(CO)6 (M=Cr, Mo and W) species with KOH
1989
Reinvestigation of the reaction of M(CO)6 (M=Cr, Mo or W) with KOH has been found to provide a very convenient route to the K[M2H(CO)10] compounds (M=Cr, Mo or W). The reaction involving Cr(CO)6 yields new potassium derivatives containing [Cr2(CO)10]2− and [HCr(CO)5]− species; also K[Cr2D(CO)10] is produced from the Cr(CO)6/KOD interaction in C2D5OD. The reaction involving two different group 6 metal carbonyls yields [MM′(CO)10(μ-H)]− (MM′=CrMo, CrW or WMo) species as their K+ and PPN+ [bis(triphenylphosphine)iminium] salts.
Suzuki-Miyaura cross-coupling of arenediazonium salts catalyzed by alginate/gellan-stabilized palladium nanoparticles under aerobic conditions in wat…
2012
The use of palladium nanoparticles stabilized by natural. beads made of an alginate/gellan mixture in the Suzuki-Miyaura cross-coupling reaction of arenediazonium. tetrafluoroborates with potassium aryltrifluoroborates. (1 : 1 molar ratio) with loading as low as 0.01–0.002. mol% under aerobic, phosphine-, and base-free conditions. in water is described. The catalyst system can be reused. several times without significant loss of activity.