Transport and Magnetic Studies on the Spin State Transition of Pr_1-xCa_xCoO₃up to High Pressure

Role ofA-site cations in the metal-insulator transition inPr0.5Ca0.5CoOBarón-González1, Frontera2, García-Muñoz3 et al. 2010Phys. Rev. B395600View full textAdd to dashboardCite

“…RESULTS Figure 1 shows the dc resistivity of Pr 0.50 Ca 0.50 CoO 3 measured by the four-probe method at zero field and under an applied field of 9 T in cooling-heating cycles. In accordance with previous works, 14,16,17 ͑T͒ shows a sudden drop ͑on heating͒ at T MI Ϸ 80 K. Above T MI , the electrical resistivity is low for a polycrystalline oxide ͑about 1 m⍀ cm͒. This value is very similar to that measured in a single-crystal specimen, 21 and is comparable in magnitude with that found for Pr 0.50 Sr 0.50 CoO 3 and different RBaCo 2 O 5+␦ compounds.…”

“…[14][15][16][17][18][19] Besides, our measurements show that above 100 K, an applied field of 9 T scarcely affects the resistivity and, in fact, slightly enlarges with the field. This demonstrates that the mobility of itinerant electrons does not depend on the magnetic arrangement of the core spins ͑t 2g 5 ͒.…”

“…[14][15][16][17][18][19][20][21][22] This compound presents, on cooling a sudden increase in the resistivity, usually described as a metal to insulator transition ͑MIT͒. It is accompanied by an anisotropic cell anomaly and a sudden large cell volume contraction.…”

Suppression of the metal-insulator transition by magnetic field in (Pr1−yYy)0.7Ca0.3CoO3 (y = 0.0625)

“…7 A distinct behavior takes place in some Pr-based mixed-valence cobaltites, in which the crossover to lower spin states acquires a form of first-order transition of metal-insulator (MI) type. This transition was observed for the first time in oxygen stoichiometric Pr 0.5 Ca 0.5 CoO 3 and was reported as having a pronounced peak in heat capacity and sharp changes in magnetic susceptibility, electrical resistivity, thermopower, and unit cell volume at T MI-SS $ 90 K. 8,9 The same phenomenon was evidenced later for analogous systems with lower calcium content, provided that they were either subjected to high pressures (physical pressure) 10 or the praseodymium sites were suitably doped by yttrium or smaller rare-earth cations like Sm, Gd, and Tb (chemical pressure). 10,11 Some empirical rules for the appearance of the MI transition were derived with regard to the values of cationic radii at the perovskite A-sites and their variance (size mismatch).…”

“…This transition was observed for the first time in oxygen stoichiometric Pr 0.5 Ca 0.5 CoO 3 and was reported as having a pronounced peak in heat capacity and sharp changes in magnetic susceptibility, electrical resistivity, thermopower, and unit cell volume at T MI-SS $ 90 K. 8,9 The same phenomenon was evidenced later for analogous systems with lower calcium content, provided that they were either subjected to high pressures (physical pressure) 10 or the praseodymium sites were suitably doped by yttrium or smaller rare-earth cations like Sm, Gd, and Tb (chemical pressure). 10,11 Some empirical rules for the appearance of the MI transition were derived with regard to the values of cationic radii at the perovskite A-sites and their variance (size mismatch). 11 It was found that the key to this specific MI-SS transition was a significant shift from mixed-valence Co 3þ /Co 4þ ions to pure Co 3þ ion, enabled by the simultaneous change in valence of some Pr 3þ ions into Pr 4þ ions.…”