Ferroelectricity of Ca9Fe(PO4)7 and Ca9Mn(PO4)7 ceramics with polar whitlockite-type crystal structure

Year 2020, Volume: 41 Issue: 2, 559 - 564, 25.06.2020

Umut Adem

https://doi.org/10.17776/csj.723752

Cited By: 1

Abstract

Ca9Fe(PO4)7 is a member of the double phosphate family having polar whitlockite-type crystal structure. The phase transition from the room temperature polar R3c to the high temperature non-polar R c phase has been called a ferroelectric phase transition using complementary experiments such as temperature dependent second harmonic generation and dielectric constant measurements however no ferroelectric hysteresis measurement has been reported. In order to be able to call these polar materials ferroelectric, measurement of a saturated ferroelectric hysteresis loop is necessary to demonstrate that the electrical polarization of these materials is switchable. In order to realize this goal, we have synthesized Ca9Fe(PO4)7 as well as structurally identical Ca9Mn(PO4)7 using solid state synthesis. Crystal structure of the ceramics were confirmed using Rietveld refinement of the x-ray diffraction (XRD) patterns. Differential scanning calorimetry (DSC) measurements revealed phase transition temperatures of 848 and 860 K for Ca9Fe(PO4)7 and Ca9Mn(PO4)7, respectively. Our ferroelectric hysteresis measurements and current electric field loops (I-E) derived from the hysteresis loops showed that the loops cannot be saturated and the direction of the electrical polarization of both materials cannot be switched up to the largest applied electric field of 100 kV/cm. Possible origins of this behaviour are discussed.

Keywords

Ferroelectricity, Phosphates, Rietveld Refinement, Phase transitions

Supporting Institution

Izmir Institute of Technology

Project Number

BAP2015İYTE29

Thanks

This work is supported by İzmir Institute of Technology via BAP Project with the project number 2015İYTE29. We thank IZTECH Department of Chemical Engineering for the DSC experiments and Celal Bayar University’s DEFAM for the use of XRD.

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