Phase equilibria in the La-Me-Co-O (Me=Ca, Sr, Ba) systems

Abstract

Abstract. The phase equilibria of the La-Me-Co-O systems (Me = Ca, Sr and Ba) were studied in air at 1100 ~ Two types of solid solution of general composition LavxMexCoO~_8 and (Lal.y Mey)2CoO 4 were found to exist in the systems. The limiting composition of Lal_xMexCoO3 ~ lies at x = 0.8 for Me = Sr, Ba and between 0.3-0.5 for Me = Ca. It is shown that the rhombohedral distortion of the perovskite type Lal_xMe• decreases while x increases. Lal_xMexCoO3_~ (Me = Sr, Ba) shows an ideal cubic structure at x -0.5. The stability range of (La1_yMey)2CoO 4 was found to be 0.25 < y < 0.35 for Me = Ca, 0.3 _<y < 0.55 for Me = Sr and 0.3 < y < 0.375 for Me = Ba.All phases have tetragonal K2NiF4-type crystal structure. Based on the XRD and neutron diffraction patterns of quenched samples, the phase diagrams (Gibbs triangles) are constructed for all systems.The phase equilibrium at low oxygen pressure is shown for the example of the La-Sr-Co-O system. The decomposition mechanism of Lal_xSrxCoO3_ ~ at 1100 ~ for the samples with 0.5 < x < 0.8 within the oxygen pressure range -0.678 > log(Po2) > -2.25 can be written as follows: Lal_ x, Sr• ~, = n Lal_x,,Srx,,CoO3_5,, + m SrCoO2.5 + q/2 O: where x' > x". The decomposition mechanism of Lal_xSrx CoO3_~ for the samples with x < 0.5 within the oxygen pressure range -2.25 > log(Po2) > -3.55 changes and can be written as follows: Lal_xSr• ~, = r Lax_x,Srx,COO3_5,, + w (Lal_y,Sry,)2CoO 4 + v CoO + f/2 02. The results are shown in "logPo2-composition" diagrams.

Phase Equilibria, Crystal Structure, and Properties of Intermediate Oxides in the Sm2O3–SrO–CoO System

“…Such a significant difference in the phase relationship that appears between the Nd‐ and Sm‐containing systems in the row of Ln 2 O 3 –SrO–CoO systems, is similar to that appearing in the row of Ln 2 O 3 –BaO–CoO systems. The formation of the La 1– x Ba x CoO 3– δ solid solution takes place for Ln = La,, while smaller‐sized rare‐earth elements, starting from Pr, form the single‐phase double perovskite LnBaCo 2 O 6– δ , which coexists with LnCoO 3 or BaCoO 3– δ ,, depending on the overall composition of the sample.…”

Thermodynamic modeling of the Sr–Co–Fe–O system

“…Nonetheless, deviation of assessed thermodynamic data from first principles results [23] was minimal. For Sr 3 Co 2 O 7 , A 0 and B 0 in Eq.5 were adjusted such as to make the phase stable at 1373 K in air in accordance with the findings from Aksenova et al and Cherepanov et al [34,65].…”

Phase equilibria and thermodynamic properties of oxide systems on the basis of rare earth, alkaline earth and 3d-transition (Mn, Fe, Co) metals. A short overview of

“…Phase equilibrium in systems with T = Co Phase equilibria in systems La-MCo-O (M = Ca, Sr, Ba) been studied quite extensively in several papers [92][93][94][95][96] at different temperatures and atmospheric pressure (Fig. 7-9).…”

“…The introduction of alkaline earth metal in the lanthanum sublattice increases the average oxidation state of cobalt in the solid solution (La 1-y M y ) 2 CoO 4 , thereby stabilizing the phase with the structure of the K 2 NiF 4 type [93][94][95][96]102]. The regions of existence of solid solutions at T = 1100 °C and =0.21 ATM are in the range of compositions 0.25≤у≤0.3 for M = Ca [92,95]; 0.30≤у≤0.55 for М = Sr [94]; 0.300≤у≤0.375 for М = Ba [92,96].…”

“…The annealing of samples at atmospheric pressure and 885 °C allowed us to obtain single-phase samples in the range of compositions 0≤x≤0.2 [93] at 1100 °C by the authors [92,95], the boundary of existence was drawn between x =0.3 and x =0.4, while after annealing the oxides at 1200 OC region of existence of solid solutions extends up to x = 0.5 [97,98]. The solid solutions La 1-x Ca x CoO 3 crystallize in the orthorhombic cell, in this case the reduction of the rhombohedral distortion with increasing x values [97] is observed.…”