Phase stability, electronic structures, and superconductivity properties of the BaPb_1−xBi_xO₃ and Ba_1−xK_xBiO₃ perovskites

Abstract

Abstact With extensive first‐principles calculations, we investigate the phase stability, electronic structures, and superconductivity properties of the BaPb1−xBixO3 (BPBO) and Ba1−xKxBiO3 (BKBO) perovskites with the cubic (C), tetragonal (T), and orthorhombic (O) phases. Our calculations show that the tetragonal superconducting phases of both perovskites are metastable. However, the orthorhombic phase of the BPBO perovskite in the superconductivity region is only slightly more stable than the tetragonal phase. The small energy difference between the T and O phases and the discontinuous T‐to‐O phase transition account for the experimentally observed coexistence of the T and O phases. On the other hand, the BKBO perovskite involves a large energy difference between the T and O phases, which induces a low equilibrium temperature of the discontinuous T‐to‐O phase transition, in agreement with the experimental observation that the tetragonal BKBO is maintained down to low temperatures. Moreover, the electronic structures of both BPBO and BKBO superconductors show a flat band near the Fermi level, which is favorable for superconductivity. Furthermore, we find that the longer the total length of the flat band segment is, the higher the critical temperature of the BPBO or BKBO perovskite is. This key finding could be generalized straightforwardly to other unconventional superconductors and can be used to design and find optimal composition with maximum Tc for new unconventional superconductors.

The chemistry of aminoguanidine derivatives – preparation, crystal structure, thermal properties, and molecular docking studies of aminoguanidinium salts of several carboxylic acids

“…Some selective BChE inhibitors have been reported to increase acetylcholine levels and reduce the formation of abnormal amyloid that occurs in Alzheimer's disease [35]. Guanidinium groups were recently shown to act as an allosteric site in an allosteric hydrolase model by supramolecular combination of adamantylguanidiniumand Cu(II)-complex of tris(2-aminoethyl)amine modified cyclodextrin [36]. In the present investigation, the binding efficacy of compounds 2 and 4 with human BChE was examined as it is crucial to understanding the biological significance of aminoguanidine derivatives.…”

CO2 laser-induced precipitation of CdSxSe1−x nanoparticles in a borosilicate glass: A new approach for the localized growth of quantum dots

“…However, such a thermal process does not authorize any spatial localization of the QDs inside the matrix, since the whole sample is subjected to homogeneous crystallization. On the contrary, laser irradiation methods have been shown to allow the local growth of several types of NCs in various kinds of matrices [7][8][9][10][11][12][13]. These methods have been proven to be particularly efficient in the case of porous xerogels that can be locally doped with various kinds of metal or semiconductor nanoparticles by using different radiations (from UV to NIR) in different regimes (from continuous-wave CW to femtosecond pulses) [9][10][11][12][13].…”

“…These methods have been proven to be particularly efficient in the case of porous xerogels that can be locally doped with various kinds of metal or semiconductor nanoparticles by using different radiations (from UV to NIR) in different regimes (from continuous-wave CW to femtosecond pulses) [9][10][11][12][13]. Concerning dense glasses, the scarce works devoted to the production of nanoparticles through light irradiation techniques all make use of a focused femtosecond laser beam and of a subsequent thermal annealing [7,8]. Those techniques involving IR short pulses generally lead to very tight and spatially resolved doped micro-zones in the glasses.…”

EFECTS OF CHEMICAL COMPOSITION ON THE MICROSTRUCTURE AND PROPERTIES OF THE CU-Ge-Sb ALLOYS

“…Considering that, to our knowledge, no studies on the ternary Cu-Ge-Sb system can be found in literature, thermodynamic assessment was based on already well-known binary sub-systems (Cu-Ge [21], Ge-Sb [22] and Cu-Sb [23]). A list of phases that are possibly present in the studied ternary system and their crystallographic data are given in Table 1.…”