Correlation of magnetic resonance (EPR, ssNMR) parameters and crystal-microstrain in marbles as a tool to probe their provenance

Abstract

Marbles constitute a significant family of materials, for antiquities, as well as modern constructions. Herein, we have studied Greek marbles, using electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (ssNMR) spectroscopies, focusing on their structural microenvironment. Spin-Hamiltonian parameters derived from EPR spectra of naturally occurring ⁵⁵Mn²⁺ (S = 5/2, I = 5/2) atoms in marbles, were studied as structural-probes. EPR data at 300 K provide a library of ⁵⁵Mn²⁺ zero-field-splitting parameters (E, D). The effect of temperature (300 up to 700 K) on ⁵⁵Mn²⁺-ZFS (E, D) and the strain of the D-tensor (D_strain) was studied by high-temperature EPR spectroscopy. The EPR data, combined with ¹³C-ssNMR, provide detailed physicochemical information of the calcite and dolomite crystal phases in the marbles. In parallel, we have analyzed the lattice-microstrain (ε₀) of the marbles’ crystallites using high-resolution XRD data. Analysis of the correlation between the D-values of Mn²⁺ centers and (ε₀)-XRD, reveals trends that reflect the provenance of the marbles. In this context, we discuss the correlation between the D-values of Mn²⁺ centers and (ε₀)-microstrain as a novel tool to elucidate the provenance of marbles.