165 research outputs found
High-pressure neutron study of the morphotropic PZT: phase transitions in a two-phase system
In piezoelectric ceramics the changes in the phase stabilities versus stress
and temperature in the vicinity of the phase boundary play a central role. The
present study was dedicated to the classical piezoelectric,
lead-zirconate-titanate (PZT) ceramic with composition
Pb(ZrTi)O at the Zr-rich side of the morphotropic phase
boundary at which both intrinsic and extrinsic contributions to
piezoelectricity are significant. The pressure-induced changes in this
two-phase (rhombohedral +monoclinic at room temperature and
above 1 GPa pressures) system were studied by high-pressure neutron
powder diffraction technique. The experiments show that applying pressure
favors the phase, whereas the phase transforms continuously to the
, which is favored at elevated temperatures due to the competing entropy
term. The phase transformation is discontinuous. The
transformation contributes to the extrinsic piezoelectricity. An important
contribution to the intrinsic piezoelectricity was revealed: a large
displacement of the cations (Zr and Ti) with respect to the oxygen anions
is induced by pressure. Above 600 K a phase transition to a cubic phase took
place. Balance between the competing terms dictates the curvature of the phase
boundary. After high-pressure experiments the amount of rhombohedral phase was
larger than initially, suggesting that on the Zr-rich side of the phase
boundary the monoclinic phase is metastable.Comment: 6 figure
Photocatalytic Degradation of Methylene Blue by Fe/ZnO/SiO 2
The photocatalytic activity of Fe/ZnO/SiO2 catalysts under visible-light irradiation for the degradation of methylene blue was evaluated. The effect of pH, illumination time, amount of catalyst loaded, and initial dye concentration on the degradation efficiency of methylene blue was investigated. The results reveal that the optimum photocatalytic oxidation conditions of methylene blue are as follows: pH=4 and illumination time is 30 min, the amount of catalyst loading is 0.075 g/L and 50 ppm methylene blue dye concentration. Under these conditions, the removal efficiency of methylene blue was 100%
Multidirectional Synthesis of Substituted Indazoles via Iridium-Catalyzed C–H Borylation
Replacing Conventional Carbon Nucleophiles with Electrophiles: Nickel-Catalyzed Reductive Alkylation of Aryl Bromides and Chlorides
Iridium-Catalyzed Borylation of Pyrene: Irreversibility and the Influence of Ligand on Selectivity
Synthesis of Allylsilanes and Dienylsilanes by a One-Pot Catalytic C−H Borylation−Suzuki−Miyaura Coupling Sequence
Directed Ortho Borylation of Phenol Derivatives Catalyzed by a Silica-Supported Iridium Complex
Rhodium catalysed dehydrogenative borylation of alkenes: Vinylboronates via C-H activation
We present herein a high yield, highly selective catalytic synthesis of vinylboronate esters (VBEs), including 1,1-disubstituted VBEs, from alkenes without significant hydrogenation or hydroboration, using the simple catalyst precursor, trans-[RhCl(CO)(PPh3)(2)] (1), and the diboron reagents B(2)pin(2) (2a, pin = pinacolato = OCMe2CMe2O) or B(2)neop(2) (2b, neop = neopentylglycolato = OCH2CMe2CH2O), or the monoboron reagent HBpin, all of which are commercially available. The reactions were conducted at 80 degrees C using conventional heating, or in a microwave reactor at 150 degrees C
Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse
This article is also available through American Chemical Society Authorchoice Open Access at http://dx.doi.org/10.1021/acs.chemrev.6b00193Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.T.B.M. thanks the DFG and the University of Würzburg for
support. S.A.W. thanks Chris Vogels for helpful discussions and
NSERC of Canada for support
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