A series of nanocrystalline Gd₂Zr₂O₇ powders has been studied using a combination of X-ray diffraction and X-ray spectroscopy with synchrotron radiation. It has been shown that isothermal annealing of an X-ray amorphous mixed hydroxide first leads to the formation of an oxide nanomaterial with a defect fluorite structure and clearly pronounced nonequivalence of the local environment of the Gd³⁺ and Zr⁴⁺ ions. Increasing heat treatment temperature results in initiation and growth of nanodomains with pyrochlore-type superstructure ordering of cations inside bulkier crystallites of defect fluorite. To adequately describe the evolution of the real nanocrystalline structure of gadolinium zirconate, a combination of X-ray structural methods sensitive to the averaged crystal structure and local atomic structure should be used.

X-ray diffraction with synchrotron radiation has been used for comparative analysis of crystal structure evolution in Ln₂Hf₂O₇ (Ln = Sm-Dy) complex oxides with a fluorite-pyrochlore structure, synthesized by isothermal annealing of mixed hydroxides. It has been shown that heat treatment of the precursor in the temperature range 600–700°C initiates the formation of nanocrystallites with a fluorite structure. Long-range cationic ordering of the pyrochlore type appears in Ln₂Hf₂O₇ (Ln = Sm-Tb) samples once a definite crystal size has been achieved at temperatures ≥1200°C. In Dy₂Hf₂O₇ samples, a defect fluorite structure persists in the entire range of heat-treatment temperatures.

Thin-film ferroelectric doped hafnia has emerged as a promising candidate for non-volatile computer memory devices due to its CMOS compatibility. The ferroelectricity in thin-film HfO₂ is defined by the polar orthorhombic phase, whose stabilization depends on various parameters, such as doping species, stress, thickness, crystallization annealing temperature, etc. The concentration of oxygen vacancies is yet another parameter affecting the stabilization of the ferroelectric phase in HfO₂ thin films. Here, we report on the effect of oxygen vacancies introduced in Y-doped HfO₂ (HYO) films during reactive pulsed laser deposition on their ferroelectric properties, which we systematically study by correlating structural and electrical properties. Among different techniques, near-edge x-ray absorption fine structure analysis is successfully employed to distinguish between structurally similar ferroelectric orthorhombic and paraelectric tetragonal phases. It is shown that oxygen vacancies introduced at a certain concentration in HYO films can be used as a tool to control the phase composition as well as to decrease the formation energy (crystallization temperature) of the ferroelectric phase. Based on these results, we demonstrate a back-end-of-line compatible ferroelectric HYO capacitor device with competitive functional properties.

It has been established that the process of producing the Ln_{2 + x} Me_{2 − x} O_{7 − x/2} (Ln = Gd, Dy; Me = Zr, Hf) nanocrystals by calcination of hydroxides, which, in turn, have been produced by coprecipitation of metal salts, includes several stages. At the beginning, the X-ray amorphous structure of the precursors remains unchanged during dehydration; during subsequent heating to 600–700°C, nanocrystals with a disordered fluorite structure begin to be formed. An increase in the temperature above 700°C leads to an increase in the size of crystallites (coherent scattering regions). This process is accompanied by changes occurring in their local structure. In the nanocrystalline powders of Cd₂Hf₂O₇ and Gd₂Zr₂O₇ synthesized at 1200°C (6 h), the pyrochlore-type superstructure with the lattice parameters doubled relative to fluorite has been revealed. It has also been found that, possibly, the Dy₂HfO₅ sample at 1600°C (3 h) has a modulated structure.