Charge ordering inNi1+/Ni2+nickelates:La4

Abstract

Ab initio calculations allow us to establish a close connection between the Ruddlesden-Popper layered nickelates and cuprates not only in terms of filling of d-levels (close to d 9 ) but also because they show Ni 1+ (S=1/2)/Ni 2+ (S=0) stripe ordering. The insulating charge ordered ground state is obtained from a combination of structural distortions and magnetic order. The Ni 2+ ions are in a low-spin configuration (S=0) yielding an antiferromagnetic arrangement of Ni 1+ S=1/2 ions like the long-sought spin-1/2 antiferromagnetic insulator analog of the cuprate parent materials. The analogy extends further with the main contribution to the bands near the Fermi energy coming from hybridized Ni-d x 2 −y 2 and O-p states. 7,8 . As the n=3 and n=2 members of the series, they have a formal Ni valence of +1.33 and +1.5, respectively, which being noninteger should correspond to metallic behavior, yet both are insulating. The NiO 2 slabs are separated by fluorite structure LaO blocking layers that make the inter-trilayer/bilayer coupling very weak. The lack of apical oxygen ions reduces the interplane separation substantially and opens a large crystal field splitting for the e g states with the d x 2 −y 2 state lying higher in energy than d z 2 . The d z 2 orbitals hybridize along the z direction giving rise to n molecular subbands. Depending on the relative magnitude of the crystal field splitting and Hund's rule coupling, the ground state can be either high spin (HS) and insulating or low spin (LS) and metallic as depicted in Fig.

Fermiology and electron dynamics of trilayer nickelate La4Ni3O10

“…This has recently been overcome for trilayer nickelates through the use of special high-pressure floating-zone image furnaces, which now enable single crystals of these nickelates to be prepared 10 . In the planar-trilayer nickelate La 4 Ni 3 O 8 , recent studies 10, 12 have revealed stripe charge ordering with a phase transition at 105 K. As for La 4 Ni 3 O 10 , a charge–density wave instability has been predicted below the metal-to-metal transition around 140 K 13, 14 .…”

Reduction of the thermal conductivity of the thermoelectric material ScN by Nb alloying

“…[1][2][3][4][5][6][7][8] Scandium nitride (ScN) is one of them and is an n-type semiconductor with a reported indirect band gap of around 0.9 eV 9,10 . It possesses both a high carrier concentration (10 and has a low electrical resistivity of around 300 µΩcm.…”

Charge-stripe order, antiferromagnetism, and spin dynamics in the cuprate-analog nickelate La4Ni3O8

“…2 and listed in Table I. It is customary [5,6,16,23] to describe magnetic and stripe structure in La 4 Ni 3 O 8 using the setting F 4/mmm, in which basal-plane unit vectors are rotated 45 • to define a face-centered square lattice of Ni ions. The lattice constants in these directions are then √ 2 times the Ni-Ni nearest neighbor distance a in the basal plane.…”

“…Ab initio calculations by Botana et al [23] yielded stripe charge order from a combination of structural distortion and AFM order, in which Ni 2+ ions have spin S = 0, and Ni 1+ S = 1/2 ions order antiferromagnetically, similar to the spin-1/2 insulating antiferromagnetism of the cuprate parent materials. In this result the valences of corresponding Ni1 and Ni2 ions in a trilayer are the same.…”

“…In this result the valences of corresponding Ni1 and Ni2 ions in a trilayer are the same. Two 2D supercells of the observed stripe pattern and the proposed 2D AFM order in a single Ni layer [23] are shown in Fig. 1.…”