Mg doping effect on high-pressure behaviors of apatite-type lanthanum silicate

• The high-pressure behavior of La10Si5.8Mg0.2O26.8 has been probed up to 33.0 GPa.
• A reversible phase transition has been observed at ∼16.1 GPa.
• The phase transition is attributed to the tilting of the Si/MgO4 tetrahedra.
• La10Si5.8Mg0.2O26.8 exhibits higher transition pressure and lower compressibility.
• The corresponding behaviors should be related to Mg doping effect.

We report a reversible phase transition in Mg doped lanthanum silicate La10Si5.8Mg0.2O26.8 at 16.1 GPa and room temperature. The phase transition reduces the symmetry from P63/m to P63 and is attributed to a tilting of the Si/MgO4 tetrahedra. The high-pressure behavior of the sample is followed by in situ angle-dispersive X-ray diffraction in a diamond anvil cell. The high-pressure P63 phase exhibits a higher compressibility than the initial P63/m structure. Furthermore, we observe that the transition pressure in the Mg doped system is elevated by ∼1.6 GPa compared to the previously reported undoped La10Si6O27 system and that the initial compressibility in the P63/m phase is lower. This behavior should be related to the larger size and less rigidness of MgO4 tetrahedra than SiO4 tetrahedra. The relevant mechanism is discussed in present paper.

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