High‐Pressure Studies of Correlated Electron Systems
Pau JorbaAlexander RegnatAnh TongMarc SeifertA. BauerMichael SchulzChristian FranzA. SchneidewindS. KunkemöllerK. JenniM. BradenAndre DeyerlingM. A. WildeJ. S. SchillingC. Pfleiderer
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Tuning the electronic properties of transition‐metal and rare‐earth compounds by virtue of changes of the crystallographic lattice constants offers controlled access to new forms of order. The development of tungsten carbide (WC) and moissanite Bridgman cells conceived for studies of the electrical resistivity up to 10 GPa, as well as bespoke diamond anvil cells (DACs) developed for neutron depolarization studies up to 20 GPa is reviewed. For the DACs, the applied pressure changes as a function of temperature in quantitative agreement with the thermal expansion of the pressure cell. A setup is described that is based on focusing neutron guides for measurements of the depolarization of a neutron beam by samples in a DAC. The technical progress is illustrated in terms of three examples. Measurements of the resistivity and neutron depolarization provide evidence of ferromagnetic order in SrRuO 3 up to 14 GPa close to a putative quantum phase transition. Combining hydrostatic, uniaxial, and quasi‐hydrostatic pressure, the emergence of incipient superconductivity in CrB 2 is observed. The temperature dependence of the electrical resistivity in is consistent with emergent Kondo correlations and an enhanced coupling of magneto‐elastic excitations with the conduction electrons at low and intermediate temperatures, respectively.Keywords:
Diamond anvil cell
Hydrostatic pressure
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Abstract Design and general description of diamond anvil cells, developed for neutron diffraction studies of powder and single crystal samples, are given. Some aspects of high pressure neutron diffraction experiments are discussed.
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Powder Diffraction
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Skutterudite compounds have recently attracted much attention from the viewpoint of both their potential as improved thermoelectric materials and their variety of electrical and magnetic properties, including exotic superconductivity, quadrupole ordering and anomalous metal-insulator transition. High-pressure synthesis is a powerful technique to prepare skutterudite compounds. In this article, the high-pressure synthesis of skutterudite compounds and their physical properties are reviewed.
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Starting from element La,Ni,Co and Sb powders,nominal La_xNi_(0.2)Co_(3.8)Sb_(12)(x=0.1,0.3,0.5,0.7) n-type filled Skutterudite was prepared by mechanical alloying(MA) and subsequent hot pressing(HP).The effect of the La filling fraction on phase formation and thermoelectric properties was studied in this paper.It was found that single phase Skutterudite could be obtained when the powders milled for 10h were hot pressed at 650℃ for 2h and the lattice parameters increase with increasing the La filling fraction.The thermal conductivity was greatly decreased by filling rear-earth element La into the voids of Skutterudite structure.As a result,the La_(0.5)Ni_(0.2)Co_(3.8)Sb_(12) Skutterudite exhibits a maximum figure of merit of 0.33 at about 750 K.
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We report here on the transport properties at high
temperature of partially Nd filled Co4Sb12 skutterudites. The
NdxCo4Sb12 (0 ≤ x ≤ 0.05) compounds were prepared by a
powder metallurgy technique. The electrical resistivity,
thermopower, Hall coefficient, and thermal conductivity
have been measured between 300 and 800 K. Influence on
the thermoelectric performance of the introduction of Nd in
the skutterudite cell is discussed. Some complementary
results on NdxCo4-yNiySb12 are also introduced.
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Solid-state physics
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P-type filled skutterudite BayFeCo3Sb12 compounds were synthesized using a two-step solid-state reaction method. The effects of Ba on thermoelectric properties of BayFeCo3Sb12 were investigated. The results indicate that the electrical conductivity decreased with increasing Ba filling fraction, which the carrier concentration dramatically dependences on. The Seebeck coefficients are improved than the unfilled CoSb3 in the middle temperature range, which is obtained 235μVK-1 of Ba1.0FeCo3Sb12. The lattice thermal conductivity decreased evidently with the Ba filling fraction, which is obtained 2.2 Wm-1K-1 of Ba1.0FeCo3Sb12. The maximum figure of merit ZTmax of Ba0.8FeCo3Sb12 is 0.75 at 850K.
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Atmospheric temperature range
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Raman scattering spectra have been measured for the unfilled skutterudite CoP3 and for the filled skutterudites RT4X12 (R= La, Ce, Pr and Nd, T=Fe and Os, and X=Sb and P). For the P‐skutterudite, the energies of two Ag phonons and one Eg phonon decrease with rare‐earth filling, while, for the Sb‐skutterudite, the energies of the observed phonons do not change significantly. In order to clarify this filling effect microscopically, a normal mode analysis has been performed using a GF matrix method. The following differences due to the filling effect have been found for the P‐ and Sb‐skutterudites: the interaction between pnictogens on the cage becomes weaker for the P‐skutterudite, while it does not change significantly for the Sb case.
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Atmospheric temperature range
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