Anisotropic thermal expansion and electronic transitions in the Co₃BO₅ ludwigite

Abstract

The thermal expansion affects the electronic state of Co3+ ions triggering the spin-state crossover and following the charge-ordering transition without changing the symmetry.

Temperature- and Field-Induced Transformation of the Magnetic State in Co2.5Ge0.5BO5

“…The expansion is evidently anisotropic with sharp expansion along the b - and c- axes. This effect can be compared to the large PTE phenomenon found for Co 3 BO 5 , caused by the flexibility of the [Co 2+ O 6 ] infinite framework …”

“…The substitution-induced variations of a, b, and c parameters ] infinite framework. 16 The next observation is that there is a clear tendency of the lattice parameters to saturate at high ionic radii, like Sn, Zr, and Hf. This may indicate an approach to the upper limit of the lattice expansion associated with the extensibility of boron− oxygen triangles.…”

“…As a result, the ludwigites might undergo a charge ordering. The iron ludwigite Fe 3 BO 5 shows the charge-ordering transition accompanied by a structural transformation and semiconductor–semiconductor transition at T CO = 283 K. , An electronic transition associated with charge delocalization was recently discovered in Co 3 BO 5 …”

“…The iron ludwigite Fe 3 BO 5 shows the charge-ordering transition accompanied by a structural transformation and semiconductor−semiconductor transition at T CO = 283 K. 14,15 An electronic transition associated with charge delocalization was recently discovered in Co 3 BO 5 . 16 Ludwigites crystallize in orthorhombic symmetry and contain two types of fundamental building blocks: MeO 6 oxygen octahedra and BO 3 triangles. The metal ions are distributed over four crystallographically nonequivalent positions M1 (2a), M2 (2b), M3 (4g), and M4 (4h).…”

“…The thermal expansion study of Co 3 BO 5 revealed that [Co 2+ O 6 ] ∞ layers have high flexibility resulting in a large positive thermal expansion effect (PTE) in the bc-plane. 16 The anomalous negative thermal expansion phenomenon (NTE) along the a-axis originates from the joint effect of the rigid BO 3 triangles and more flexible M4O 6 octahedra. This effect can be tuned by the M4 site substitution.…”