2 research outputs found
Downscaling Effect on the Superconductivity of Pd<sub>3</sub>Bi<sub>2</sub>X<sub>2</sub> (X = S or Se) Nanoparticles Prepared by Microwave-Assisted Polyol Synthesis
Pd<sub>3</sub>Bi<sub>2</sub>S<sub>2</sub> and Pd<sub>3</sub>Bi<sub>2</sub>Se<sub>2</sub> have been successfully prepared in the form
of nanoparticles with diameters of ∼50 nm by microwave-assisted
modified polyol synthesis at low temperatures. The composition and
morphology of the samples have been studied by means of powder X-ray
diffraction as well as electron microscopy methods, including X-ray
intensity mapping on the nanoscale. Superconducting properties of
the as-prepared samples have been characterized by electrical resistivity
measurements down to low temperatures (∼0.2 K). Deviations
from the bulk metallic behavior originating from the submicrometer
nature of the samples were registered for both phases. A significant
critical-field enhancement up to 1.4 T, i.e., 4 times higher than
the value of the bulk material, has been revealed for Pd<sub>3</sub>Bi<sub>2</sub>Se<sub>2</sub>. At the same time, the critical temperature
is suppressed to 0.7 K from the bulk value of ∼1 K. A superconducting
transition at 0.4 K has been observed in nanocrystalline Pd<sub>3</sub>Bi<sub>2</sub>S<sub>2</sub>. Here, a zero-temperature upper critical
field of ∼0.5 T has been estimated. Further, spark plasma-sintered
Pd<sub>3</sub>Bi<sub>2</sub>S<sub>2</sub> and Pd<sub>3</sub>Bi<sub>2</sub>Se<sub>2</sub> samples have been investigated. Their superconducting
properties are found to lie between those of the bulk and nanosized
samples
Synthesis of a Cu-Filled Rh<sub>17</sub>S<sub>15</sub> Framework: Microwave Polyol Process Versus High-Temperature Route
Metal-rich,
mixed copper–rhodium sulfide Cu<sub>3−δ</sub>Rh<sub>34</sub>S<sub>30</sub> that represents a new Cu-filled variant
of the Rh<sub>17</sub>S<sub>15</sub> structure has been synthesized
and structurally characterized. Copper content in the [CuRh<sub>8</sub>] cubic cluster was found to vary notably dependent on the chosen
synthetic route. Full site occupancy was achieved only in nanoscaled
Cu<sub>3</sub>Rh<sub>34</sub>S<sub>30</sub> obtained by a rapid, microwave-assisted
reaction of CuCl, Rh<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>4</sub> and thiosemicarbazide at 300 °C in just 30 min; whereas
merely Cu-deficient Cu<sub>3−δ</sub>Rh<sub>34</sub>S<sub>30</sub> (2.0 ≥ δ ≥ 0.9) compositions were realized
via conventional high-temperature ceramic synthesis from the elements
at 950 °C. Although Cu<sub>3−δ</sub>Rh<sub>34</sub>S<sub>30</sub> is metallic just like Rh<sub>17</sub>S<sub>15</sub>, the slightly enhanced metal content has a dramatic effect on the
electronic properties. Whereas the Rh<sub>17</sub>S<sub>15</sub> host
undergoes a superconducting transition at 5.4 K, no signs of the latter
were found for the Cu-derivatives at least down to 1.8 K. This finding
is corroborated by the strongly reduced density of states at the Fermi
level of the ternary sulfide and the disruption of long-range Rh–Rh
interactions in favor of Cu–Rh interactions as revealed by
quantum-chemical calculations