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Perturbed angular correlation spectroscopy combined with ab initio electronic structure calculations is used to unravel the structural phase transition path from the low -temperature polar structure to the high -temperature structural phase in Ca 3 Ti 2 O 7 , a hybrid improper ferroelectric. The experimental procedure, conducted at ISOLDE, explores the unique features of a local probe environment approach by monitoring the evolution of the electric field gradient tensor at the calcium sites. The local environments, observed above 1057 K, confirm a structural phase transition from the A 2 1 am symmetry to an orthorhombic Acaa symmetry in the Ca 3 Ti 2 O 7 crystal lattice, disagreeing with the frequently reported avalanche structural transition from the polar A 2 1 am phase to the aristotype I 4 / mmm phase. Moreover, the EFG temperature dependency, within the A 2 1 am temperature stability, is shown to be sensitive to the recently proposed Ca 3 Ti 2 O 7 ferroelectric polarization decrease within the 500-800 K temperature range.