AER/Inorganic Chemistry Seminar – Md. Wahad Uz Zaman
About the event
Speaker: Md. Wahad Uz Zaman
Group: Dr. Kevin Kittilstved
Title: Spin Hamiltonian perspectives on Cr-Doped Srn+1TinO3n+1: understanding electronic structure, zero-field splitting, and their impact on photocatalytic performance
Abstract
Transition-metal doping of perovskite oxides is an effective strategy for tuning their electronic structure and photocatalytic activity, yet the role of local symmetry, lattice dimensionality, and defect–dopant interactions remains not well understood. In this presentation, we examine the spin-Hamiltonian parameters of substitutional Cr3+ dopants in members of the Ruddlesden–Popper series Srn+1TinO3n+1, focusing on the n = ∞ (SrTiO3)1, 2 and n = 1 (Sr2TiO4)3, 4 phases. Electron paramagnetic resonance (EPR) spectroscopy is used to probe the local electronic structure of Cr3+ (S = 3/2), revealing how deviations from octahedral symmetry induce zero-field splittings and g-anisotropy of the ground state. In SrTiO3, the cubic TiO6 environment yields nearly isotropic g-values and no zero-field splitting, whereas the axially compressed TiO6 units in Sr2TiO4 produce a finite axial zero-field splitting parameter (D) and anisotropic g-tensor. These differences are rationalized using ligand-field theory and perturbative spin–orbit coupling, highlighting the sensitivity of Cr3+ electronic structure to local lattice distortions. Correlating these spin-Hamiltonian parameters with optical absorption and defect formation provides insight into how lattice symmetry and dimensionality govern charge localization, defect energetics, and photocatalytic behaviour. This comparative framework motivates the investigation of Cr-doped Sr3Ti2O7 (n = 2), an intermediate Ruddlesden–Popper phase that offers a tunable balance between three-dimensional and two-dimensional electronic confinement, and is expected to exhibit distinct zero-field splitting, defect chemistry, and photocatalytic response.
References
1. Lehuta, K. A.; Kittilstved, K. R., Reversible control of the chromium valence in chemically reduced Cr-doped SrTiO3 bulk powders. Dalton Transactions 2016, 45 (24), 10034-10041.
2. Harrigan, W. L.; Kittilstved, K. R., Reversible modulation of the Cr3+ spin dynamics in colloidal SrTiO3 nanocrystals. The Journal of Physical Chemistry C 2018, 122 (46), 26652-26657.
3. Lehuta, K. A.; Haldar, A.; Zhou, D.; Kittilstved, K. R., Spectroscopic study of the reversible chemical reduction and reoxidation of substitutional Cr ions in Sr2TiO4. Inorganic Chemistry 2017, 56 (15), 9177-9184.
4. Yu, J.; Xu, X., Fluorination over Cr doped layered perovskite Sr2TiO4 for efficient photocatalytic hydrogen production under visible light illumination. Journal of Energy Chemistry 2020, 51, 30-38.