Continuous synthesis of high quality CdSe quantum dots in supercritical fluids

We demonstrate in here a powerful scalable technology to synthesize continuously high quality CdSe quantum dots (QDs) in supercritical hexane. Using a low cost, highly thermally stable Cd-precursor, cadmium deoxycholate, the continuous synthesis is performed in 400 mu m ID stainless steel capillaries resulting in CdSe QDs having sharp full-width-at-half-maxima (23 nm) and high photoluminescence quantum yields (45-55%). Transmission electron microscopy images show narrow particles sizes distribution (sigma <= 5%) with well-defined crystal lattices. Using two different synthesis temperatures (250 degrees C and 310 degrees C), it was possible to obtain zinc blende and wurtzite crystal structures of CdSe QDs, respectively. This synthetic approach allows achieving substantial production rates up to 200 mg of QDs per hour depending on the targeted size, and could be easily scaled to gram per hour.

Bioenergy and climate change mitigation: an assessment

Bioenergy deployment offers significant potential for climate change mitigation, but also carries considerable risks. In this review, we bring together perspectives of various communities involved in the research and regulation of bioenergy deployment in the context of climate change mitigation: Land-use and energy experts, land-use and integrated assessment modelers, human geographers, ecosystem researchers, climate scientists and two different strands of life-cycle assessment experts. We summarize technological options, outline the state-of-the-art knowledge on various climate effects, provide an update on estimates of technical resource potential and comprehensively identify sustainability effects. Cellulosic feedstocks, increased end-use efficiency, improved land carbon-stock management and residue use, and, when fully developed, BECCS appear as the most promising options, depending on development costs, implementation, learning, and risk management. Combined heat and power, efficient biomass cookstoves and small-scale power generation for rural areas can help to promote energy access and sustainable development, along with reduced emissions. We estimate the sustainable technical potential as up to 100EJ: high agreement; 100-300EJ: medium agreement; above 300EJ: low agreement. Stabilization scenarios indicate that bioenergy may supply from 10 to 245EJyr(-1) to global primary energy supply by 2050. Models indicate that, if technological and governance preconditions are met, large-scale deployment (>200EJ), together with BECCS, could help to keep global warming below 2 degrees degrees of preindustrial levels; but such high deployment of land-intensive bioenergy feedstocks could also lead to detrimental climate effects, negatively impact ecosystems, biodiversity and livelihoods. The integration of bioenergy systems into agriculture and forest landscapes can improve land and water use efficiency and help address concerns about environmental impacts. We conclude that the high variability in pathways, uncertainties in technological development and ambiguity in political decision render forecasts on deployment levels and climate effects very difficult. However, uncertainty about projections should not preclude pursuing beneficial bioenergy options.

Ferromagnetism and the effect of free charge carriers on electric polarization in the double perovskite Y2NiMnO6

The double perovskite Y2NiMnO6 displays ferromagnetic transition at T-c approximate to 81 K. The ferromagnetic order at low temperature is confirmed by the saturation value of magnetization (Ms) and also validated by the refined ordered magnetic moment values extracted from neutron powder diffraction data at 10 K. This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The cation-ordered P2(1)/n nuclear structure is revealed by neutron powder diffraction studies at 300 and 10 K. Analysis of the frequency-dependent dielectric constant and equivalent circuit analysis of impedance data take into account the bulk contribution to the total dielectric constant. This reveals an anomaly which coincides with the ferromagnetic transition temperature (T-c). Pyrocurrent measurements register a current flow with onset near T-c and a peak at 57 K that shifts with temperature ramp rate. The extrinsic nature of the observed pyrocurrent is established by employing a special protocol measurement. It is realized that the origin is due to reorientation of electric dipoles created by the free charge carriers and not by spontaneous electric polarization at variance with recently reported magnetism-driven ferroelectricity in this material.

Magnetic structures and magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied by neutron powder diffraction

The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at T-N(Fe/Mn) approximate to 295K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, T-SR(Fe/Mn) approximate to 26K where a spin-reorientation transition occurs in the Fe/Mn sublattice and T-N(R) approximate to 2K where Tb-ordering starts to manifest. At 295 K, the magnetic structure of the Fe/Mn sublattice in TbFe0.5Mn0.5O3 belongs to the irreducible representation Gamma(4) (G(x)A(y)F(z) or Pb'n'm). A mixed-domain structure of (Gamma(1) + Gamma(4)) is found at 250K which remains stable down to the spin re-orientation transition at T-SR(Fe/Mn) approximate to 26K. Below 26K and above 250 K, the majority phase (>80%) is that of Gamma(4). Below 10K the high-temperature phase Gamma(4) remains stable till 2K. At 2 K, Tb develops a magnetic moment value of 0.6(2) mu(B)/f.u. and orders long-range in F-z compatible with the Gamma(4) representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe0.5Mn0.5O3 and, in addition, reveals the presence of mixed magnetic domains. The ratio of these magnetic domains as a function of temperature is estimated from Rietveld refinement of neutron diffraction data. Indications of short-range magnetic correlations are present in the low-Q region of the neutron diffraction patterns at T < T-SR(Fe/Mn). These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe0.5Mn0.5O3. (C) 2016 AIP Publishing LLC.

Magnetic structures and magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied by neutron powder diffraction

The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at T-N(Fe/Mn) approximate to 295K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, T-SR(Fe/Mn) approximate to 26K where a spin-reorientation transition occurs in the Fe/Mn sublattice and T-N(R) approximate to 2K where Tb-ordering starts to manifest. At 295 K, the magnetic structure of the Fe/Mn sublattice in TbFe0.5Mn0.5O3 belongs to the irreducible representation Gamma(4) (G(x)A(y)F(z) or Pb'n'm). A mixed-domain structure of (Gamma(1) + Gamma(4)) is found at 250K which remains stable down to the spin re-orientation transition at T-SR(Fe/Mn) approximate to 26K. Below 26K and above 250 K, the majority phase (>80%) is that of Gamma(4). Below 10K the high-temperature phase Gamma(4) remains stable till 2K. At 2 K, Tb develops a magnetic moment value of 0.6(2) mu(B)/f.u. and orders long-range in F-z compatible with the Gamma(4) representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe0.5Mn0.5O3 and, in addition, reveals the presence of mixed magnetic domains. The ratio of these magnetic domains as a function of temperature is estimated from Rietveld refinement of neutron diffraction data. Indications of short-range magnetic correlations are present in the low-Q region of the neutron diffraction patterns at T < T-SR(Fe/Mn). These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe0.5Mn0.5O3. (C) 2016 AIP Publishing LLC.

Integrals of motion for one-dimensional Anderson localized systems

Anderson localization is known to be inevitable in one-dimension for generic disordered models. Since localization leads to Poissonian energy level statistics, we ask if localized systems possess `additional' integrals of motion as well, so as to enhance the analogy with quantum integrable systems. We answer this in the affirmative in the present work. We construct a set of nontrivial integrals of motion for Anderson localized models, in terms of the original creation and annihilation operators. These are found as a power series in the hopping parameter. The recently found Type-1 Hamiltonians, which are known to be quantum integrable in a precise sense, motivate our construction. We note that these models can be viewed as disordered electron models with infinite-range hopping, where a similar series truncates at the linear order. We show that despite the infinite range hopping, all states but one are localized. We also study the conservation laws for the disorder free Aubry-Andre model, where the states are either localized or extended, depending on the strength of a coupling constant. We formulate a specific procedure for averaging over disorder, in order to examine the convergence of the power series. Using this procedure in the Aubry-Andre model, we show that integrals of motion given by our construction are well-defined in localized phase, but not so in the extended phase. Finally, we also obtain the integrals of motion for a model with interactions to lowest order in the interaction.

Magnetic structures and magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied by neutron powder diffraction

The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at T-N(Fe/Mn) approximate to 295K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, T-SR(Fe/Mn) approximate to 26K where a spin-reorientation transition occurs in the Fe/Mn sublattice and T-N(R) approximate to 2K where Tb-ordering starts to manifest. At 295 K, the magnetic structure of the Fe/Mn sublattice in TbFe0.5Mn0.5O3 belongs to the irreducible representation Gamma(4) (G(x)A(y)F(z) or Pb'n'm). A mixed-domain structure of (Gamma(1) + Gamma(4)) is found at 250K which remains stable down to the spin re-orientation transition at T-SR(Fe/Mn) approximate to 26K. Below 26K and above 250 K, the majority phase (>80%) is that of Gamma(4). Below 10K the high-temperature phase Gamma(4) remains stable till 2K. At 2 K, Tb develops a magnetic moment value of 0.6(2) mu(B)/f.u. and orders long-range in F-z compatible with the Gamma(4) representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe0.5Mn0.5O3 and, in addition, reveals the presence of mixed magnetic domains. The ratio of these magnetic domains as a function of temperature is estimated from Rietveld refinement of neutron diffraction data. Indications of short-range magnetic correlations are present in the low-Q region of the neutron diffraction patterns at T < T-SR(Fe/Mn). These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe0.5Mn0.5O3. (C) 2016 AIP Publishing LLC.

Magnetic structures and magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied by neutron powder diffraction

The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at T-N(Fe/Mn) approximate to 295K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, T-SR(Fe/Mn) approximate to 26K where a spin-reorientation transition occurs in the Fe/Mn sublattice and T-N(R) approximate to 2K where Tb-ordering starts to manifest. At 295 K, the magnetic structure of the Fe/Mn sublattice in TbFe0.5Mn0.5O3 belongs to the irreducible representation Gamma(4) (G(x)A(y)F(z) or Pb'n'm). A mixed-domain structure of (Gamma(1) + Gamma(4)) is found at 250K which remains stable down to the spin re-orientation transition at T-SR(Fe/Mn) approximate to 26K. Below 26K and above 250 K, the majority phase (>80%) is that of Gamma(4). Below 10K the high-temperature phase Gamma(4) remains stable till 2K. At 2 K, Tb develops a magnetic moment value of 0.6(2) mu(B)/f.u. and orders long-range in F-z compatible with the Gamma(4) representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe0.5Mn0.5O3 and, in addition, reveals the presence of mixed magnetic domains. The ratio of these magnetic domains as a function of temperature is estimated from Rietveld refinement of neutron diffraction data. Indications of short-range magnetic correlations are present in the low-Q region of the neutron diffraction patterns at T < T-SR(Fe/Mn). These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe0.5Mn0.5O3. (C) 2016 AIP Publishing LLC.