Pressure-enhanced Insulating State and Trigonal Distortion Relaxation in Geometrically Frustrated Pyrochlore Eu₂Sn₂O₇

Abstract

The geometrically frustrated pyrochlore Eu2Sn2O7 is an insulator with slight trigonal lattice distortion at ambient condition. High pressure is applied to this system to investigate the responses of structural evolution, optical emission and electrical transport properties. In situ high pressure synchrotron X-ray diffraction, Raman spectroscopy, and photoluminescence studies are performed in Eu2Sn2O7 up to 31.2 and 34.1 GPa, respectively. The abrupt change of the oxygen atomic position without breaking the crystal symmetry is accompanied by disappearing of Raman mode involving SnO6 octahedron distortion around 17.8 GPa. It indicates a pressure-induced second-order iso-structural transition, which suppresses the trigonal distortion in the SnO6 octahedron but enhances the local symmetry distortion of EuO8 hexahedron. Anomalous luminescence of the Eu3+ 4f–4f transition is observed, which confirms the enhancement of EuO8 hexahedral distortion at high pressure region. In situ high-pressure electrical transport property is measured by alternating current (AC) impedance spectroscopy up to 32.5 GPa. A rapid increase in resistance with gain of 4 orders of magnitude by applied pressure is observed until 16.6 GPa, and it is followed by a slight decreasing to the highest pressure measured here. All these observations indicate a pressure-enhanced trigonal lattice distortion before the transition pressure, and thus it will enlarge an opening gap at the Fermi energy, followed by releasing distortion at higher pressures.

Experimental and Simulation Insights into Local Structure and Luminescence Evolution in Eu3+-Doped Nanocrystals under High Pressure

“…Eu 3+ ions acted as a probe to indicate the tendency of local symmetry during the compression–decompression cycle. Unlike the evolution trend reported in YF 3 NCs, YPO 4 NCs, and other Eu 3+ -doped materials, , the higher pressure led a higher local symmetry around Eu 3+ ions in β-NaGdF 4 :Eu 3+ NCs. In situ angle dispersive synchrotron X-ray diffraction was conducted to investigate the structure evolution of β-NaGdF 4 :Eu 3+ NCs.…”

High-pressure versus isoelectronic doping effect on the honeycomb iridate Na2IrO3

“…In comparison, for pyrochlore iridates like Eu 2 Ir 2 O 7 and similar compounds like Eu 2 Sn 2 O 7 bulk moduli B 0 in the range 166 to 285 GPa with B ′ 0 in the range 3.8 to 28 are reported. [65][66][67][68] For the perovskite iridate Sr 2 IrO 4 B 0 = 174 ± 5 GPa and B ′ 0 = 4.0 ± 0.7 is found [69], while for the stripy-honeycomb γ-Li 2 IrO 3 B 0 around 130 GPa was reported recently [70]. Therefore, the bulk modulus for the honeycomb iridate Na 2 IrO 3 is smaller than for pyrochlore, perovskite, and stripy-honeycomb iridates, i.e., Na 2 IrO 3 is more compressible.…”

Abnormal Pressure‐Induced Photoluminescence Enhancement and Phase Decomposition in Pyrochlore La2Sn2O7

“…A pressure‐induced spin transition, bandgap change, and lattice distortion have been reported in some pyrochlores before, but no study has solely focused on the effect of photoluminescence (PL) in the pyrochlore system . However, we previously reported a PL change with pressure in a pyrochlore, Eu 2 Sn 2 O 7 , which exhibited an interesting pressure‐dependent evolution of the Eu 3+ 4f electronic structure . Even though the luminescence properties of ns 2 ions have been extensively studied, near‐infrared (NIR) region PL is rarely observed in BaSnO 3 .…”