The crystal chemistry of AM2O4 oxometallates

Paramagnetic and antiferromagnetic resonances have been observed for powder samples of Li 2 CuO 2 in submillimeter wave region using pulsed magnetic fields at temperatures from 1.9 K to 265 K. At the paramagnetic state, the g -values have been determined to be g // =2.30 and g ⊥ =2.01. The line-width estimated from the powder signal increases as the frequency increases. Antiferromagnetic resonance modes along the principal axes have been clearly observed even in the powder samples below the Neel temperature and explained by the conventional antiferromagnetic resonance theory. It has been found that the easy axis is parallel to the direction of g // and the anisotropy is almost uniaxial and fairly strong. This fact is quite different from other antiferromagnetic copper oxides. Obtained parameters by AFMR are A =90 mol/emu, A x ′ =0.061 A, A y ′ =-0.021 A, A z ′ =-0.040 A, Γ x ′ =-0.028 A, Γ y ′ =0.018 A and Γ z ′ = 0.010 A.

EPR and AFMR of Bi2CuO4 in Submillimeter Wave Region

A thermodynamic evaluation of the ternary Bi-Cu-O system has been made and a set of parameters consistently describing the system at 1 bar total pressure has been determined. The ternary system contains a liquid phase which is continuous at high temperature and separates into a metal liquid and an oxide liquid at low temperature and the ternary compound Bi2CuO4 in addition to the binary compounds. Concentration/temperature diagrams are given for the Bi2O3-CuOx system at oxygen partial pressures of 1, 0.21 and 10−5 bar, as well as a potential diagram. Selected isothermal sections at 1100 and 1473 K are also presented. Available experimental data are rather limited and often show a relatively large scatter, but nevertheless make it possible to determine a sufficient set of thermodynamic parameters.

Thermodynamic Evaluation of the Bi-Cu-O System

As CuBi2O4 is an emerging p-type semiconductor for applications as a photocathode in photoelectrochemical (PEC) solar fuel production, there is much to be understood about the uniqueness and common...

CuBi2O4: Electronic Structure, Optical Properties, and Photoelectrochemical Performance Limitations of the Photocathode

The title materials display anomalous electrical, magnetic and optical properties. They have the characteristics of Mott insulators showing high electrical resistance and ligand-field optical spectra, but at the same time they adopt a magnetic ground state which is neither of Curie-Weiss type nor indeed of some standard antiferromagnetically ordered condition. The observed state is one of lowish, isotropic, and almost temperature-independent paramagnetism. The authors have studied the magnetic properties of Sc-doped TiOX, seeking possible indications of the existence of the resonant valence bond or RVB state-the state currently suggested by some to be responsible for high-temperature superconductivity in the mixed-valence cuprates. It is necessary to distinguish between RVB and some extreme case of magnetic frustration in these S=1/2, 2D oxyhalide systems. The authors' tentative conclusion is that TiOX presents an RVB ground state which Sc doping renders glassy and static.

https://iopscience.iop.org/article/10.1088/0953-8984/5/13/014/pdf

TiOCl, TiOBr-are these RVB d1, S=1/2 materials? The results of scandium substitution set in the context of other S=1/2 systems of current interest for high-temperature superconductivity and the metal-insulator transition

The structure and magnetic properties of Bi 2 CuO 4 have been studied by neutron and X-ray diffraction, magnetic susceptibility and magnetization measurements. Three-dimensional (3D) and anisotropic antiferromagnetism is revealed for this compound rather than the previously anticipated one-dimensional one. Long-range antiferromagnetic order associated with a ferromagnetic stacking of Cu 2+ spins along the [001] axis starts to develop below T N =42 K. A magnetic moment of 0.85±0.05 µ B /Cu which is larger than those of Cu 2+ spins in the two-dimensional Heisenberg antiferromagnets such as La 2 CuO 4 and Sr 2 CuCl 2 O 2 reflects the 3D character in Bi 2 CuO 4 . A non-linear magnetization curve under an inplane magnetic field is analyzed quantitatively by a continuous spin rotation in the (001) plane.

Ken-ichi Takada

Papers

Three-Dimensional Antiferromagnetic Order and Anisotropic Magnetic Properties in Bi 2 CuO 4