Iron oxide nanoparticles have become of great interest in the medical field for their potential uses in areas such as biomagnetic imaging and hypothermia cancer treatment. Traditionally, particles for these applications are produced through batch-based methodologies. Herein, we demonstrate an alternative continuous flow production method for the synthesis of Fe 3 O 4 iron oxide nanoparticles. Advantages of continuous flow over the batch method include consistent formation of uniformly spherical particles, thorough mixing of reactants, and capacity for highvolume particle production. In this study, a continuous flow reaction mechanism was proposed in which stoichiometric control of reactants had the potential to control final particle size. The project was conducted under the supposition that the iron oleate/ligand ratio in the precursor was the greatest size control factor, with a higher ratio resulting in smaller particles. The resulting particles produced by this continuous method were characterized by high-resolution transmission electron microscopy, X-ray diffraction, and magnetometry.
We report a novel synthesis strategy to prepare high-performance bulk polycrystalline Pr-doped SrTiO 3 ceramics. A large thermoelectric power factor of 1.3 W m −1 K −1 at 500°C is achieved in these samples. In-depth investigations of the electronic transport and microstructure suggest that this significant improvement results from a substantial enhancement in carrier mobility originating from the formation of Pr-rich grain boundaries. This work provides new directions to higher performance oxide thermoelectrics as well as possibly other properties and applications of this broadly functional perovskite material. ■ INTRODUCTIONThe interest in the electronic transport properties of SrTiO 3 (strontium titanate)-based perovskite systems originated with the report of superconductivity in oxygen-deficient semiconducting strontium titanate. 1 In the following years, the functionality of SrTiO 3 -based materials has expanded over a wide range of intriguing phenomena and properties including quantum paraelectricity, 2 giant dielectric permittivity, 3,4 roomtemperature ferroelectricity, 5 room-temperature photoluminescence, 6,7 mixed ionic-electronic conductivity, 8,9 bistable electrical resistance switching, 10,11 and interfacial two-dimensional electron gas 12,13 and more recently has exhibited some very interesting thermoelectric properties. 14 Exploration of thermoelectric properties of strontium titanate and other oxides began after the report of Terasaki et al. in 1997 showed that p-type NaCoO 2 single crystal possesses a higher room temperature power factor (defined herein as PF = α 2 σT, where α is the Seebeck coefficient, σ is the electrical conductivity, and T is the temperature in Kelvin) of ∼1.5 W m −1 K −1 as compared to ∼1.2 W m −1 K −1 for Bi 2 Te 3 , a state-of-the-art commercial thermoelectric material. 15 Further investigations of oxide thermoelectrics highlighted layered alkali or alkaline-earth cobaltite compounds (Na x CoO 2 16 and Ca 3 Co 4 O 9 ), 17 K x RhO 2 , 18 and recently BiCuSeO 19 as the most promising ptype oxide materials, while SrTiO 3 , CaMnO 3 , 20 ZnO, 21 and very recently (Sr x Ba 1−x )Nb 2 O 6 22,23 were being investigated as potential n-type candidates.The interest in the thermoelectric (TE) properties of SrTiO 3 ("STO") arose when Okuda et al. reported a high roomtemperature power factor of ∼1.08 W m −1 K −1 for heavily Ladoped STO single crystals. 14 The electronic transport in SrTiO 3 can be tuned over a wide range of physical properties. The electrical conductivity of n-type STO materials can be achieved over a very broad range: from insulating to metallic through a combination of either of the two following doping mechanisms: (i) substitutional doping of Sr 2+ or Ti 4+ sites with higher valence elements (e.g., La 3+ for Sr 2+ sites or Nb 5+ for Ti 4+ sites) and/or (ii) creating oxygen vacancies. Moreover, a large carrier effective mass (m* ∼ 2−16m e ) 24−26 and conduction band degeneracy leads to a large Seebeck coefficient at high carrier concentrations. However, a low carrier mo...
experiments will be repeated with 100% longitudinally polarized surface muons (4 MeV) when the intensity needed is available. With these muons the crystal size can be matched to the secondary electron's range so that, every time a primary (selective) interaction occurs, all the energy released by the interaction causes decomposition of only the one enantiomer involved in the primary step.In these latter experiments there is a serious dilution effect on any selectivity shown by the primary particle, due to the extensive radiation chemical effects of secondary electrons (hays) of very much lower polarization, which also interact with the racemic medium. In order to avoid this, some experiments were conducted with an equal mixture of enantiomeric crystals, rather than a racemate on the molecular level. When irradiated with polarized high-energy protons (500 MeV) the crystals gave results which indicated less than a 2% s e l e c t i~i t y ;~~ but these (98) T. Q.Rates of COz escape from (loll) cleavage surfaces of calcite (CaC0,) single crystals were measured at temperatures from 893 to 1073 K and at C02 background pressures, Pcoz, from
glected. From the present knowledge and understanding of this method, only average velocities for SCG can be determined. The method is particularly suitable for revealing the onset of SCG and in studying the qualitative nature of SCG as a function of strain rate and temperature.The DT method is simple for K,,. evaluation if several test samples are available. The average value of K,, determined for NC-132 Si,N4 at 20°C was =4.1 MN/m3I2. The DT method is especially suitable for determining crack velocities and the corresponding stress intensity, K,, for SCG. The V-K data obtained at high temperatures (2 1300°C) using the DT method followed the siinple power relation, V =AKp, and showed that the parameter n does not vary significantly with temperature in the SCG region for a given environment (air). The value of n at 1400°C is e 5 . 2 5 .
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