Abstract
The evolution of iron local vibrational mode (Fe LVM) and phase transitions in n-type iron-doped indium phosphide (InP:Fe) were investigated at ambient temperature. In-situ angle-dispersive X-ray diffraction measurements revealed that InP:Fe starts to transform from zinc-blende (ZB) to rock-salt (RS) structure around 8.2(2) GPa and completes around 16.0(2) GPa. The Raman shift of both transverse and longitudinal optical modes increases monotonically with increasing pressure, while their intensities become indiscernible at 11.6(2) GPa, suggesting that the pressure-induced phase transition is accompanied by significant metallization. In contrast, originally absent at ambient pressure, the Raman shift of Fe LVM appears at ∼420 cm−1 near 1.2 GPa and exhibits a dome shape behavior with increasing pressure, reaching a maximum value of ∼440 cm−1 around 5 GPa, with an apparent kink occurring around the ZB-RS transition pressure of ∼8.5(2) GPa. The Fe K-edge X-ray absorption near edge structure (XANES) confirmed the tetrahedral site occupation of Fe3+ with a crystal field splitting parameter Δt = 38 kJ·mole−1. Our calculations indicate that the energy parameters governing the phase transition are Δt = 0.49 and Δo = 1.10 kJ·mole−1, respectively, both are much smaller than Δt = 38 kJ·mole−1 at ambient.
Highlights
All spectra were recorded with a Leitz UM 32 microscope objective and 3 accumulations at 1 second and 600 seconds integration time with ~50 mW power on the sample for each ruby fluorescence and Raman spectrum, respectively
The ADXRD and Raman data presented in this study were collected at room temperature and the pressure transmitting medium (PTM) used was the methanol-ethanol mixture with a 4:1 ratio
As mentioned above, the 4:1 methanol-ethanol mixture should be a suitable PTM for the present high-pressure study
Summary
As mentioned above that, when the doped Fe atom replaces the In atom, its exact valence state may lead to very different local symmetries at the original site of In atom. Taking a closer look at the pre-edge features and comparing to the previous report by Ney et al.[16] we noticed that some Fe-Fe related Fe clusters might have contributed to the XANES spectrum. Our results is comparable to the previous reported by Cesca et al.[3], which the averaged Fe-P distance of tetrahedral geometry is around 2.36(2) Å This tetrahedral geometry of local Fe site consistent with the XANES line shape analysis in pre-edge peak around ~7114 eV. Based on the XANES and EXAFS results, we believe that the oxidation state of Fe in InP structure is mainly in Fe3+ and the Fe is bonded with four P atoms in tetrahedral geometry[19]. It is noted that, since the EXAFS spectra were taken with the
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