Formation and properties of Ca2+ substituted (Ce0.2Zr0.2Ti0.2Sn0.2Hf0.2)O2 high-entropy ceramics

Novel entropy-stabilized fluorite oxides with multifunctional properties

“…5(a)) shows that Ce seems to be essential to form a single-phase fluorite structure, as also suggested by Chen et al in a recent study. 37…”

“…36 Also, Chen et al , showed a series of samples where each element in Zr 0.2 Hf 0.2 Ce 0.2 Ti 0.2 Sn 0.2 O 2 is replaced by Ca to further enlarge the fluorite family and concluded that Ce is important to realize single-phase high-entropy fluorite oxides. 37 In this article, we explore a set of novel entropy-stabilized fluorite oxides in which the constituent elements are chosen to ensure a positive change in enthalpy (Δ H mix > 0, which originates from differences in the ionic radii, electronegativity, and crystal structure of individual simple oxides) and high configurational entropy (equimolar concentration of five different elements) and in this process, we also reinvestigate the first reported high-entropy fluorite oxides by Chen et al , 6 and observe a peculiar structural behaviour on the surface and bulk in Zr 0.2 Hf 0.2 Ce 0.2 Ti 0.2 Sn 0.2 O 2 , attributed to the possible reduction of Ce 4+ for this combination of elements. Furthermore, a deeper understanding of single-phase formation in high-entropy fluorite oxides is developed considering the possible role of oxygen vacancies and oxidation states of cations to synthesize new compositions and novel entropy-stabilized fluorite oxides: Zr 0.2 Hf 0.2 Ce 0.2 Sn 0.2 Mn 0.2 O 2− δ , Zr 0.2 Hf 0.2 Ti 0.2 Mn 0.2 Ce 0.2 O 2− δ , Zr 0.225 Hf 0.225 Ti 0.225 Mn 0.225 Ce 0.1 O 2− δ , Zr 0.2 Hf 0.2 Ti 0.2 Mn 0.2 Ce 0.1 Ta 0.05 Fe 0.05 O 2− δ synthesized using standard solid-state reaction routes are reported for the first time.…”

“…36 Also, Chen et al, showed a series of samples where each element in Zr 0.2 Hf 0.2 Ce 0.2 Ti 0.2 Sn 0.2 O 2 is replaced by Ca to further enlarge the uorite family and concluded that Ce is important to realize single-phase high-entropy uorite oxides. 37 In this article, we explore a set of novel entropy-stabilized uorite oxides in which the constituent elements are chosen to ensure a positive change in enthalpy (DH mix > 0, which originates from differences in the ionic radii, electronegativity, and crystal structure of individual simple oxides) and high congurational entropy (equimolar concentration of ve different elements) and in this process, we also reinvestigate the rst reported high-entropy uorite oxides by Chen et al, 6 standard solid-state reaction routes are reported for the rst time. These novel high-entropy uorite samples are further screened using cyclic thermal treatment to establish the congurational entropy dominated phase stability which is further supported by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) techniques.…”