Structural transitions under high-pressure in a langasite-type multiferroic Ba3TaFe3Si2O14

• Structural properties of new multiferroic Ba3TaFe3Si2O14 at high pressure.
• Two structural transitions were proved by XRD, Raman and Mössbauer spectroscopy.
• The transition at 5 GPa is isostructural one within the initial trigonal phase.
• At 20 GPa trigonal-to-monoclinic transition occurred with volume decrease of 9%.

The iron containing langasite family compound Ba3Ta57Fe3Si2O14 was studied at high pressure up to 30 GPa at room temperature by means of in situ X-ray diffraction, Raman and Mössbauer spectroscopies in diamond anvil cell. Two structural transitions at pressures ∼5 and ∼20 GPa are observed. At ∼5 GPa, the low-pressure trigonal P321 phase undergoes phase transition to the most likely P3 structure as manifested by slight increase in the c/a ratio and by anomalies of the Mössbauer and Raman spectra parameters. At ∼20 GPa, the first order phase transition to monoclinic structure occurred with a drop of unit cell volume by 9%. The appearance of the ferroelectric state at such transitions is discussed in connection with the multiferroic properties.

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