Insight to the crystallization process of functional materials deposited as thin films in an amorphous state is essential when phase pure samples of specific polymorphs are sought for utilization of performance aspects or fundamental studies. In this work, we report on controlled crystallization of α- and β-MoO₃ polymorphs from amorphous MoO₃ thin films produced by atomic layer deposition (ALD). The MoO₃ films are amorphous as deposited. Our experiments show that β-MoO₃ starts to crystallize from amorphous MoO₃ at a surprisingly low temperature of 185 °C, only 20 °C above the adopted ALD deposition temperature. Thin films of the β-MoO₃ polymorph start slowly to convert into α-MoO₃ at temperatures above 300 °C; however, long holding times are required to obtain phase pure products. High-quality thin film samples (electrodes) were characterized by electrochemical cycling towards lithium, demonstrating that α- and β-MoO₃ transfers into the same chemical state during cycling and that amorphous MoO₃ undergoes less change upon cycling.

Orthoferrites are a class of magnetic materials with a magnetic ordering temperature above 600 K, predominant $G$-type antiferromagnetic ordering of the Fe-spin system and, depending on the rare-earth ion, a spin reorientation of the Fe spin taking place at lower temperatures. ${\mathrm{DyFeO}}_3$ is of particular interest since the spin reorientation is classified as a Morin transition with the transition temperature depending strongly on the Dy-Fe interaction. Here, we report a detailed study of the magnetic and structural properties of microcrystalline ${\mathrm{DyFeO}}_3$ powder and bulk single crystal using neutron diffraction and magnetometry between 1.5 and 450 K. We find that, while the magnetic properties of the single crystal are largely as expected, the powder shows strongly modified magnetic properties, including a modified spin reorientation and a smaller Dy-Fe interaction energy of the order of 10 μeV. Subtle structural differences between powder and single crystal show that they belong to distinct magnetic space groups. In addition, the Dy ordering at 2 K in the powder is incommensurate, with a modulation vector of 0.0173(5) $c^{*}$, corresponding to a periodicity of ∼58 unit cells.