(Hf_0.25Zr_0.25Sn_0.25Ti_0.25)O₂ high‐entropy ceramics and their microwave dielectric characteristics

Abstract

Hf 0.25 Zr 0.25 Sn 0.25 Ti 0.25 )O 2 high-entropy ceramics were designed and prepared, and their microwave dielectric characteristics were investigated together with the microstructures. The single-phase structure in space group Pbcn was determined, and the excellent microwave dielectric characteristics were achieved in the present ceramics: ε r = 25.6, Qf = 74 600 GHz at 6.5 GHz and τ f = −47 ppm/ • C. The significant improvement of Qf value was achieved with a prolonged sintering, where the dielectric constant increased slightly while the negative τ f decreased in the absolute value at first and then turned to increase. The variation tendency of microwave dielectric characteristics was deeply linked with the microstructure homogeneity, and the introduction of Hf and Sn elements to create the high-entropy ceramics resulted in the disordered state, and finally led to the improved Qf value. The present work provided an effective approach to achieve enhanced Qf value in microwave dielectric ceramics.

Novel entropy-stabilized fluorite oxides with multifunctional properties

“…Besides, the (mostly) orthorhombic nature of the XRD pattern for the powder samples agrees with the recent studies on four-component binary high-entropy oxides using similar elements. 34,35 It is seen that the XRD pattern for the bulk is similar to the XRD pattern of the precursors calcined at 1300 °C, indicating that such a mixture could be difficult to convert back to single-phase fluorite at 1500 °C due to kinetic issues. In order to avoid this possible difficulty, a new synthesis is performed where the oxide precursors are mixed using ball milling and the mixture is consolidated into pellets and is directly sintered at 1500 °C followed by quenching.…”

“…Although the XRD pattern of the pellet evidences a single-phase fluorite structure with the Fm 3̄ m space group, the powder consists of a combination of fluorite and orthorhombic structures. 34 At this stage, the origin of such a distinctive nature of XRD patterns on the surface and bulk is not very clear. Also, such an observation has never been reported in the literature for these high entropy compounds, to the best of our knowledge.…”

“…Further calcination of mixed precursors at 1300 °C results in a multiphase compound, with a main orthorhombic phase (space group: Pbcn ). 34 After consolidating the powder into thin pellets and sintering at 1500 °C for 6 hours followed by quenching, the XRD pattern of the surface of the pellet (penetration depth of the XRD beam was estimated to be a few μm) evidences a single-phase fluorite structure with no impurity within the sensitivity of the XRD. In order to assess the role of configurational entropy in the formation of the compound, this pellet was further exposed to cyclic heat treatment.…”

“…In 2018, Chen et al reported the first entropy-stabilized fluorite, Zr 0.2 Hf 0.2 Ce 0.2 Ti 0.2 Sn 0.2 O 2 with thermal conductivity ( κ ) ∼1.28 W m −1 K −1 at 300 K. 6 Furthermore, Gild et al , 32 showed a series of high-entropy fluorite oxides, followed by synthesis of (Zr 0.2 Ce 0.2 Hf 0.2 Y 0.2 Al 0.2 )O 2− δ by Wen et al 33 However, entropy-stabilization was not established in these systems (cyclic heat treatment or other methods were not shown). Ding et al , 34 and He et al , 35 reported a (Hf 0.25 Zr 0.25 Sn 0.25 Ti 0.25 )O 2 system with an orthorhombic structure (space group: Pbcn ); however, no evidence was provided to support their claim of entropy stabilization. High-entropy fluorite oxides also include reports by Djenadic et al on equiatomic rare-earth oxides having high configurational entropy (Ce 0.2 La 0.2 Sm 0.2 Pr 0.2 Y 0.2 )O 2− δ (ref.…”

A review on structure–property relationships in dielectric ceramics using high‐entropy compositional strategies

“…[1], [2], [24], [25], [29], [40][41][42][43][44]. Reproduced with permission of Springer, Elsevier, and Wiley.…”