The structural phase transition path from the low-temperature polar structure up to the highest symmetric phase in the hybrid improper ferroelectric ${\mathrm{Ca}}_3{\mathrm{Mn}}_2{\mathrm{O}}_7$ compound is here investigated at atomic scale. Measurements using the perturbed angular correlation local probe technique are combined with ab initio electronic structure calculations to observe the evolution of the electric field gradient parameters at the $\mathrm{Ca}$ site within the 10–1200 K temperature range. The results show that polar-phase clusters persist at temperatures as high as 500 K. In addition, evidence is given for a structural phase transition occurring above 1150 K. The high-temperature symmetry is here confirmed to be $I4/mmm$.

• Received 3 September 2019
• Revised 13 December 2019
• Accepted 15 January 2020

DOI:https://doi.org/10.1103/PhysRevB.101.064103

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