Crystal chemistry and structural phase transition in CaLa₂Zn_1–<i>x</i>Ca_<i>x</i>Ti₂O₉ (<i>x</i> = 0.00, 0.15, 0.30, 0.45, 0.90 and 1.00)

Abstract

Abstract Polycrystalline materials with the compositions CaLa 2 Zn 1− x Ca x Ti 2 O 9 ( x = 0.00, 0.15, 0.30, 0.45, 0.90 and 1.00) were synthesized via the conventional solid-state reaction method under ambient conditions. Their crystal structures were determined at room temperature from powder X-ray diffraction (XRPD) using the Rietveld method. For compositions with x = 0.00, 0.15, 0.30, and 0.45, the structures crystallize in the orthorhombic space group Pbnm , with the octahedra tilting in-phase along the [001] direction, and out-of-phase along the [100] and [010] directions of the pseudocubic cell; corresponding to the tilt system a − a − c + . Compositions with x = 0.90 and 1.00 adopt the monoclinic space group P 2 1 / n , with the octahedra tilting in-phase along the c axis and out-of-phase along the a and b axes, consistent with the tilt system a − b − c + . In both structural models, the frameworks consist of corner-sharing B O 6 octahedra in three dimensions. The structural distortion of the monoclinic phases indicates partial 1:1 B -site ordering between Ti 4+ (occupying the 2 c site) and a random mixture of 2/3 (Zn 2+ 1− x Ca 2+ x ) and 1/3 Ti 4+ (occupying the 2 d site). Along the c axis, the B –O1– B bond angles in the orthorhombic phases ( B = Zn(Ca2)/Ti) were calculated to be 156.3° ( x = 0.00), 157.3° ( x = 0.15), 154.8° ( x = 0.30), and 157.2° ( x = 0.45). In contrast, the Ti1–O3– B ′ bond angles in the monoclinic phases ( B ′ = Zn(Ca2)/Ti2) were found to be 158.5° ( x = 0.90) and 158.3° ( x = 1.00). These materials could have promising potential for applications in electrical and dielectric devices.