Structure, thermostability and magnetic properties of cubic Ce2-x Ti2O7 pyrochlore obtained via sol-gel preparation

Growth of a quasicrystal-related structure and superstructure for ultrathin Ce-Ti-O films on Pt(111)

Herein, oxide quasicrystal-related (OQC-R) structure and Ce-Ti-O-(3 × 3) superstructure ultrathin films were prepared on Pt(111) and characterized using scanning tunneling microscopy (STM) and low-energy electron diffraction. The OQC-R structure with dodecagonal clusters consisting of triangles, squares, and rhombuses was observed in STM images. The first discovery of the OQC-R structure with a magnetic rare earth metal expands the possibility of discovering new oxide quasicrystals with novel magnetism or superconductivity. By depositing Ti on an OQC-R ultrathin film and post-annealing, a honeycomb lattice of the Ce-Ti-O-(3 × 3) superstructure was prepared. From X-ray photoelectron spectroscopy (XPS) and resonant-photoelectron spectroscopy, the chemical states of the Ce and Ti atoms in the OQC-R structure corresponded to the Ce3+ and Ti2+ states, while those for the Ce-Ti-O-(3 × 3) superstructure corresponded to the Ce3+, Ti3+, and Ti2+ states. The phase transformation from the OQC-R structure to the Ce-Ti-O-(3 × 3) honeycomb superstructure likely occurred when the amount of Ti increased and was more oxidized. The elemental atomic density was also calibrated using XPS and Rutherford backscattering spectroscopy. These results propose tentative structural models of the OQC-R structure as Ce18Ti14O41 and the Ce-Ti-O-(3 × 3) superstructure as CeTi6O9.

Low temperature magnetic behavior and thermal expansion anomaly of cubic CeTiO3

Lanthanum-based LnBO₃ perovskite oxides have demonstrated fascinating magnetic properties and spin–lattice coupling. In this work, we report an unusual thermal expansion anomaly coupled with the magnetic ordering in the cubic CeTiO₃ with the vacancy of Ce ions. The magnetic behaviors and lattice thermal expansion at low temperature were systematically investigated using the temperature dependence of the magnetization measurements and low temperature X-ray powder diffraction. It is clearly revealed that there are two magnetic transitions in the cubic CeTiO₃ from 5 to 350 K: one is a magnetic ordering–disordering transition at 300 K and the other one might be a change of the magnetic component near 32 K. Both the magnetization and hysteresis change correspondingly upon cooling. Intriguingly, a lattice thermal expansion anomaly is found below the magnetic ordering temperature, which indicates a strong coupling of spin and lattice, i.e., a magnetovolume effect (MVE). Our findings provide the possibility of adjusting thermal expansion behavior and magnetic properties by introducing a vacancy of Ln atoms in lanthanum-based perovskite oxides.

An unusual thermal expansion anomaly with magnetic ordering in cubic CeTiO₃ was found. A magnetic ordering–disordering transition at 300 K and a change of the magnetic component near 32 K were noted. A magnetovolume effect was found below the magnetic ordering temperature.