  Simultaneous study of magnetic and electrocatalytic properties of cobaltites
under extreme conditions expands understanding of physical and chemical
processes proceeding in them with the possibility of their further practical
application. Therefore, La0.6Sr0.4CoO3 (LSCO) nanopowders have been synthesized
at different annealing temperatures tann = 850, 875, 900 C, and their
multifunctional properties have been studied comprehensively. As tann
increases, the rhombohedral perovskite structure of the LSCO becomes more
single-phase, whereas average particle size and dispersion grow. Co ions are in
mixed valence states, including major Co3+ and Co4+ components. It has been
found that the LSCO-900 shows two main Curie temperatures, TC1 and TC2,
associated with a particle size distribution. As an external hydrostatic
pressure P increases, average <TC1> and <TC2> increase from 253 and 175 K under
ambient pressure to 268 and 180 K under P = 0.8 GPa, respectively. At the same
time, the antiferromagnetic temperature TAFM and blocking temperature TB also
increase from 145 and 169 K to 158 and 170 K, respectively. The increment of
<dTC/dP> for the smaller and bigger particles is sufficiently high and equals
10 and 13 K/GPa, respectively. The magnetocaloric effect in the LSCO-900
nanopowder is relatively weak but with an extremely wide peak > 50 K that makes
this composition interesting to be used as one of the components of the
composite expanding its working temperature window. Moreover, all LSCO samples
showed excellent electrocatalytic performance for the overall water splitting
(OER) process (overpotentials only 265-285 mV at a current density of 10
mA/cm2) with minimal values for LSCO-900. Based on the XPS data, it was found
that the formation of a dense amorphous layer on the surface of the particles
ensures high stability as a catalyst (at least 24 h) during electrolysis in 1 M
KOH electrolyte.
