Microwave dielectric ceramics (MWDCs) are prone to mechanical failure, and improving the mechanical properties of MWDCs is of significance for their application under extreme conditions. Novel high-entropy R(Nb 1- x Ta x ) 2 O 6 (R = Mg 0.2 Mn 0.2 Co 0.2 Ni 0.2 Zn 0.2 ) ceramics were prepared by the solid-phase reaction method. The single-phase and composite solid solutions of the R(Nb 1- x Ta x ) 2 O 6 series were successfully prepared, as evidenced by XRD, Raman spectra, and combined with EDS energy spectrum analysis. The average grain size was found to increase with the Ta 5+ content, while the grain dispersion exhibited a trend of increasing and then decreasing, resulting in a trend of increasing and then decreasing Q× f . The replacement of Nb 5+ by Ta 5+ has been demonstrated to improve τ f and enhance the mechanical properties. An increase in Ta 5+ content from 0.5 to 0.75 results in a significant enhancement in ε r and mechanical properties, which is primarily attributed to the generation of the RTa 2 O 6 phase. When x = 1, the R(Nb 1- x Ta x ) 2 O 6 ceramics exhibit excellent microwave dielectric properties (ε r = 31.28, Q× f = 20,722, τ f = 48.36) and the most favorable mechanical properties ( H v = 7.99 GPa, σ = 882 MPa, TRS = 237.7 MPa). This study provides a new idea to improve the mechanical properties of MWDCs.
The need to develop safe solid-state lithium batteries has stimulated intense research efforts for Li + solid electrolytes. However, the low conductivity limits the development of NASICON LiZr 2 (PO 4 ) 3 (LZP) electrolyte. Here, the doping effects of Ta on the structure, surface morphologies and electrochemical properties of Li 1- x Zr 2- x Ta x (PO 4 ) 3 (LZTP, x = 0, 0.01, 0.02, 0.04, 0.06 and 0.08) solid electrolyte were analyzed. LZTP was prepared using a simple solid-state reaction route, followed by sintering at 1200 °C for 12 h. A proper content of Ta 5+ substitution for Zr 4+ is beneficial to stabilize the high conductive rhombohedral (α) phase of LZP at room temperature. Doping Ta 5+ is conducive to unblocking of Li + at the M1 site and facilitates the occupation of Li + at the M2 site, thereby expanding the pathway for Li + conduction. Rietveld refinement data demonstrated that the Zr–O and P–O bond lengths ( d Zr-O and d P-O ) increased with a decrease in Zr–O–P bond angles ( θ Zr-O-P ) as x rose. The distortions in the ZrO 6 octahedron may weaken the coulomb attraction in Li + -O 2- , resulting in a lower activation energy ( E a ) and a higher Li + conductivity. The highest room-temperature conductivity (6.06 × 10 −5 S cm −1 ) was obtained at x = 0.06, which reached 1.5 × 10 −4 S cm −1 at 50 °C. The E a was found to decrease from 0.388 eV ( x = 0) to 0.306 eV ( x = 0.06). In addition, Ta doping resulted in improved connectivity and reduced pore formation, which also contributed to the decrease in resistance. The Raman spectrum demonstrated that some phonon modes of bending vibration in PO 4 were degenerate and external modes became too weak to be observed or even disappeared as Ta content increased. This change in the modes also had an impact on the Li + conductivity. Overall, the LZTP-0.06 appears to be a promising candidate for the solid electrolyte.
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