High entropy oxides (HEOs) are a class of materials, containing equimolar portions of five or more transition metal and/or rare-earth elements. We report here about the layer-by-layer growth of HEO [(La 0.2 Pr 0.2 Nd 0.2 Sm 0.2 Eu 0.2 )NiO 3 ] thin films on NdGaO 3 substrates by pulsed laser deposition. The combined characterizations with in-situ reflection high energy electron diffraction, atomic force microscopy, and X-ray diffraction affirm the single crystalline nature of the film with smooth surface morphology. The desired +3 oxidation of Ni has been confirmed by an element sensitive X-ray absorption spectroscopy measurement. Temperature dependent electrical transport measurements revealed a first order metal-insulator transition with the transition temperature very similar to the undoped NdNiO 3 . Since both of these systems have a comparable tolerance factor, this work demonstrates that the electronic behaviors of A-site disordered perovskite-HEOs are primarily controlled by the average tolerance factor.Finding new materials and new ways to tune material's properties are essential to fulfill the demand of the constantly evolving modern technology. Transition metal oxides show various fascinating electronic and magnetic phenomena such as metal-insulator transition, superconductivity, colossal magnetoresistance, multiferroicity, skyrmions, etc., which have lots of prospect for technological applications 1-6 . Furthermore, transition metal (TM) based high entropy oxides (HEOs) are being explored in recent years to achieve tunable properties in unexplored parts of complex phase diagram 7-21 . In general, the configurational entropy of a multi-component solid solution can be enhanced by mixing a large number of cations in equiatomic proportions and a single structural phase is formed if the entropy contribution overcomes enthalpy driven phase separation (∆G mix =∆H mix -T ∆S mix ; ∆G mix , ∆H mix , ∆S mix are Gibbs free energy, enthalpy and entropy of mixing, respectively) 7,18 . After the report of the first HEO [Mg 0.2 Ni 0.2 Co 0.2 Cu 0.2 Zn 0.2 O with rocksalt structure] by Rost et al. 7 , HEOs with other structural symmetry such as perovskite 15,17 , spinel 16 have been also synthesized. However, this promising field of HEO is at a very early stage and most of the aspects of HEOs are yet to be explored experimentally. For example, it is still unknown whether the strong disorder or the average tolerance factor (t avg ) determines the electronic and magnetic behaviors of perovskite-HEOs.As a prototypical example of perovskite (ABO 3 ) series, RENiO 3 (RE= La, Pr, Nd, Sm, Eu...Lu) exhibits an interesting phase diagram as a function of tolerance factor (t= R RE +RO √ 2(RNi+RO) , where R RE , R Ni , R O are radii of RE, Ni and O, respectively) 22,23 . LaNiO 3 , the least distorted member of this series remains metallic and paramagnetic down to the lowest temperature. Bulk PrNiO 3 and NdNiO 3 (NNO) show temperature driven simultaneous transitions from an orthorhombic, paramagnetic, metallic phase to a monoclini...
For a floating bubble, in the range of Bond numbers based on an equivalent spherical radius, 0 < Boe < 1, we present analytical expressions for various shape parameters of the bubble as functions of Boe. Expressions are obtained for the radius of the rim Rr, the radius of the thin film cap Rc, the height of the top of the cap from the rim hcap, the height of the rim above the free surface hr, and the depth of the bubble cavity from the free surface Zc. To obtain these expressions, we solve equations formulated in terms of these shape parameters for the meniscus outside the bubble, the force balance of the bubble, the pressure balance at the centre line of the bubble, and geometrical constraints, after neglecting the deformation of the bubble cavity for Boe < 1. The obtained expressions are shown to match well with our experimental measurements of the shape of the bubble. In addition to these expressions, we also present simpler approximations that can be used accurately as scaling laws for these shape parameters up to Boe < 0.5.
Detection of the global 21 cm signal arising from neutral hydrogen can revolutionize our understanding of the standard evolution of the Universe after recombination. In addition, it can also be an excellent probe of dark matter (DM). Among all the DM candidates, primordial black holes (PBHs) are one of the most well motivated. Hawking emission from low-mass PBHs can have a substantial effect on the thermal and ionization history of the early Universe, and that in turn can have an imprint on the global 21 cm signal. Recently EDGES has claimed a global 21 cm signal, though SARAS 3 has rejected that claim. In this work, we investigate the sensitivities on nonspinning and spinning PBHs arising from an EDGES-like measurement of the global 21 cm signal, and find that the sensitivities will be competitive with those arising from other astrophysical observables. We show that the sensitivities can be significantly strengthened depending on various uncertain astrophysical parameters. Besides, we also derive projections on the PBH density from the absorption trough expected during the Dark Ages. Our work shows that the near future unambiguous detection of the global 21 cm absorption troughs can be an excellent probe of PBH DM.
CEBAF accelerator delivers continuous wave (CW) electron beams to three experimental Halls. In Hall A, all experiments require continuous, non-invasive current measurements and a few experiments require an absolute accuracy of 0.2 % in the current range from 1 to 180 $ A Parametric Current Transformer (PCT), manufactured by Bergoz, has an accurate and stable sensitivity of 4 $9 EXW LWV RIIVHW GULIWV DW WKH $ OHYHO RYHU WLPH preclude its direct use for continuous measurements. Two cavity monitors are calibrated against the PCT with at least 50 µA of beam current. The calibration procedure suppresses the error due to PCT's offset drifts by turning the beam on and off, which is invasive to the experiment. One of the goals of the system is to minimize the calibration time without compromising the measurement's accuracy. The linearity of the cavity monitors is a critical parameter for transferring the accurate calibration done at high currents over the whole dynamic range. The method for measuring accurately the linearity is described.
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