Research Article

Structural characterization and Charge density approximations of LaAlO₃ & La₂Zr₂O₇

Abstract

Lanthanum aluminate (LaAlO₃) and lanthanum zirconate (La₂Zr₂O₇) composite powders were synthesized by a conventional solid-state reaction using La₂O₃, Al₂O₃ and ZrO₂ as the starting materials, followed by wet ball milling and sintering at 1300 °C. Powder X-ray diffraction and Rietveld refinement were used for phase identification, quantitative phase analysis and determination of the crystallographic parameters. The refinement confirmed rhombohedral perovskite LaAlO₃ with the R3c space group as the major phase, accounting for approximately 95 wt%, whereas cubic pyrochlore La₂Zr₂O₇ with the Fd3m space group was identified as the minor phase, accounting for approximately 5 wt%. The refined structural parameters and structure factors were used for crystallographic modelling and electron-density analysis using FullProf and Visualization for Electronic and Structural Analysis (VESTA). The three-dimensional crystal structures, atomic coordination environments, bond lengths and electron-density distributions of both phases were examined. Fourier-based electron-density maps across selected crystallographic planes showed distinct charge-localization features around the La–O, Al–O and Zr–O coordination environments, indicating differences in the local bonding characteristics of the two crystalline phases. Transmission electron microscopy, high-resolution transmission electron microscopy and selected-area electron diffraction further confirmed the crystalline nature, phase formation and preferred crystallographic orientation of the synthesized powders. The combined Rietveld refinement, crystallographic modelling and electron-microscopy analyses provide a detailed description of the structural and electron-density characteristics of the LaAlO₃–La₂Zr₂O₇ composite system.

Author affiliation: G. Venkatesh: Department of Metallurgical Engineering, PSG College of Technology, Coimbatore-641 004 Tamil Nadu, India. Email: venkih07@gmail.com