Structural Phase Transition from Rhombohedral to Cubic in LaCoO<sub><b>3</b></sub>

Kobayashi, Yoshihiko; Mitsunaga, Tohru; Fujinawa, Go; Arii, Tadashi; Suetake, M; Asai, Kichizo; Harada, J.

doi:10.1143/jpsj.69.3468

Cited by 48 publications

(41 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We can clearly observe that within the instrumental resolution of the diffractometer there is neither any signature of structural transition nor appearance of any of superlattice peaks or increment in the pre-existing peak, which indicates that AFM/FM ordering is not set down to the lowest temperature, 2.8 K at the wavelength 1.48 Å, in all the samples for x¼ 0, 0.1, 0.2 and 0.3. Similar result of non-appearance of any superlattice peak and non-existence of long range ordering in pure LaCoO 3 is reported in the pure LaCoO 3 , and well documented in the literature [25][26][27]. So the Ni substitution at Co site, has not made any significant change from the point of view of magnetic behavior in this series of compounds.…”

Section: (A) and (B)supporting

confidence: 87%

Neutron diffraction studies of magnetic ordering in Ni-doped LaCoO

Rajeevan

Kumar

et al. 2015

Journal of Magnetism and Magnetic Materials

View full text Add to dashboard Cite

Section: (A) and (B)supporting

confidence: 87%

Neutron diffraction studies of magnetic ordering in Ni-doped LaCoO

Rajeevan

Kumar

et al. 2015

Journal of Magnetism and Magnetic Materials

View full text Add to dashboard Cite

“…Due to the partially filled e g level, the IS state is JT active. The degeneracy of the e g orbitals of Co 3+ ions in the LS state is expected to be lifted in the IS state by a JT distortion.All structural studies, based on powder X-ray and neutron diffraction experiments are consistently interpreted in rhombohedral R3c symmetry and no structural transitions are reported in the temperature interval 4.2K − 1248K [16,17,18,19]. A cooperative JT distortion is incompatible with this space group.…”

mentioning

confidence: 89%

Evidence for orbital ordering inLaCoO3

et al. 2003

View full text Add to dashboard Cite

We present powder and single crystal X-ray diffraction data as evidence for a monoclinic distortion in the low spin (S = 0) and intermediate spin state (S = 1) of LaCoO3. The alternation of short and long bonds in the ab plane indicates the presence of eg orbital ordering induced by a cooperative Jahn-Teller distortion. We observe an increase of the Jahn-Teller distortion with temperature in agreement with a thermally activated behavior of the Co 3+ ions from a low-spin ground state to an intermediate-spin excited state.The study of orbital degrees of freedom in transition metal (TM) oxides has gained prominent interest. Novel techniques such as Resonant X-ray Scattering and X-Ray Absorption Spectroscopy give direct information about orbital occupancy. It is realized that the orbital moments are as important as the spin moments to understand the electronic properties. Prominent examples in which the orbital degrees of freedom determine the electronic properties are the metal-insulator transitions in V 2 O 3 [1] and doped LaM nO 3 [2]. Here, spin-and orbital-induced transitions are intimately related. In the perovkites, metallicity and orbital ordering are mutually exclusive because of the large Jahn-Teller (JT) splitting of the e g orbitals [3]. Furthermore, novel ground states can be obtained such as an orbital liquid [4,5].Considerable interest in the perovskite-type LaCoO 3 originates from the puzzling nature of two transitions in this compound and the vicinity to a metal-insulator transition. The ground state of LaCoO 3 is a nonmagnetic insulator and there is no long range magnetic order at all temperatures. At low temperatures, the magnetic susceptibility increases exponentially with temperature exhibiting a maximum near 100K. At higher temperatures, a second anomaly is observed around 500K which is accompanied by a semiconductor to metal transition. The maximum at 100K was ascribed initially to a change of the spin state in the Co 3+ ions i.e. a transition from a low-spin (LS) nonmagnetic ground state (t 6 2g , S = 0) to a high-spin (HS) state (t 4 2g e 2 g , S = 2) [6,7,8,9]. In the more recent literature [10,11,12,13,14], new scenarios involving an intermediate-spin state (IS) (t 5 2g e 1 g , S = 1) have been proposed. Using LDA+U calculations, Korotin et al. [15] proposed the stabilization of the IS state due to the large hybridization between the Co-e g and O-2p levels. Due to the partially filled e g level, the IS state is JT active. The degeneracy of the e g orbitals of Co 3+ ions in the LS state is expected to be lifted in the IS state by a JT distortion.All structural studies, based on powder X-ray and neutron diffraction experiments are consistently interpreted in rhombohedral R3c symmetry and no structural transitions are reported in the temperature interval 4.2K − 1248K [16,17,18,19]. A cooperative JT distortion is incompatible with this space group. The rhombohedral distortion of the parent cubic perovskite structure consists of a deformation along the body diagonal, and preserves only one Co ...

show abstract

“…For La 0.8 Ca 0.2 CoO 3 , c/a √ 6 was found to be 0.9839. Extrapolation of the experimental data to the temperature where c/a √ 6 becomes unity and the material becomes ideal cubic shows that the rhombohedral to cubic (r → c) transition could occur clearly well above 1000 • C for pure LaCoO 3 [37], but 20% Ca doping will lower that transition to around 950 • C [33,38]. This is in good agreement with earlier observations [34] that the greater rhombohedral distortion at room temperature results in the higher transition temperature to cubic structure.…”

Section: Thermal Expansionmentioning

confidence: 99%

“…The reduced cell parameters; a/ √ 2 (circles) and c/ √ 12 (squares) are shown in (a) and (b). (×) The rhombohedral, r, to cubic, c, transition temperatures of LaCaO3 and La0.8Ca0.2CoO3 reported in Refs [37,33],. respectively.…”

mentioning

confidence: 99%