High-entropy (La0.2Dy0.2Er0.2Yb0.2Y0.2)2Zr2O7 oxide, a potential thermal barrier coating material with photoluminescence property sensitive to pressure

In this work, high-entropy (La 0.2 Dy 0.2 Er 0.2 Yb 0.2 Y 0.2 ) 2 Zr 2 O 7 oxide (RZHEO-1600) has been synthesized by using a simple solid-state reaction method and investigated as a promising thermal barrier coating (TBC) material with potential optical pressure sensing application. Compared to oxide-yttria stabilized zirconium (YSZ) and single component zirconates, RZHEO-1600 exhibits excellent thermal stability at 1600 °C and a larger thermal expand coefficient 13.5 × 10 −6  K −1 due to the high entropy effect. Its thermal conductivity (1.23–1.41 W m −1  K −1 ) and Vickers hardness (10 GPa) are lower than YSZ, while its fracture toughness (2.9 MPa m 1/2 ) is much larger. The photoluminescence (PL) emissions of RZHEO-1600 excited by 514 nm laser are assigned to 4 S 3/2  →  4 I 15/2 and 4 F 9/2  →  4 I 15/2 transitions of Er 3+ ions. The centre positions of emission peaks initially at 560 and 677 nm are sensitive to pressure, which red shift linearly with pressure coefficients of 0.178 nm/GPa (−5.650 cm −1 /GPa) and 0.223 nm/GPa (−4.932 cm −1 /GPa), respectively. Interestingly, the PL intensity ratios I 677 /I 658 and I 560 /I 547 are found to be pressure sensitive, which continuously increase during the compression. The findings of this study could serve as a new guide for the development of novel high-entropy oxide TBC materials with optical sensing applications.