Local distortions and B -site-resolved environments in Ca 2 Mn 1 − x Ti x O 4 solid solutions

A series of Ruddlesden-Popper perovskite solid solutions, Ca 2 Mn 1 − x Ti x O 4 ( 0.25 ≤ x ≤ 0.65 ) , is examined by combining density functional theory (DFT) calculations with local-scale experimental studies conducted at ISOLDE-CERN over a broad temperature range (10–1220 K). Perturbed angular correlation (PAC) spectroscopy probes the I 4 / m m m to I 4 1 / a c d structural phase transitions for all compositions between 900 and 1200 K. For x = 0.65 , measurements below 160 K show that a second structural phase condenses, coexisting with the I 4 1 / a c d phase down to 10 K. DFT structural models reproduce a key experimental observation: in the I 4 1 / a c d phase, the c lattice parameter shows only a minor increase upon Ti substitution, whereas the a b plane expands significantly, reducing the c / a ratio linearly. This anisotropic response can be attributed to a corkscrewlike mechanism, where the enhancement of in-plane B O 6 octahedral rotations induces a contraction of the rocksalt layers, thereby mitigating the expansion of the c axis. PAC data, supported by DFT calculations, demonstrate that Ca sites apically connected to MnO 6 octahedra exhibit experimentally distinguishable Electric Field Gradients from those connected to TiO 6 octahedra.