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Single-particle and collective excitations of polar water molecules confined in nano-pores within a cordierite crystal lattice.

Mikhail A BelyanchikovZ V BedranM SavinovP BednyakovP ProschekJ ProkleskaV A AbalmasovE S ZhukovaVictor G ThomasA DudkaAndriy ZhugayevychJ PetzeltA S ProkhorovV B AnzinR K KremerJ K H FischerPeter LunkenheimerAlois LoidlE UykurMartin DresselB Gorshunov
Published in: Physical chemistry chemical physics : PCCP (2022)
Recently, the low-temperature phase of water molecules confined within nanocages formed by the crystalline lattice of water-containing cordierite crystals has been reported to comprise domains with ferroelectrically ordered dipoles within the a , b -planes which are antiferroelectrically alternating along the c -axis. In the present work, comprehensive broad-band dielectric spectroscopy is combined with specific heat studies and molecular dynamics and Monte Carlo simulations in order to investigate in more detail the collective modes and single-particle excitations of nanoconfined water molecules. From DFT-MD simulations we reconstruct the potential-energy landscape experienced by the H 2 O molecules. A rich set of anisotropic temperature-dependent excitations is observed in the terahertz frequency range. Their origin is associated with the complex rotational/translational vibrations of confined H 2 O molecules. A strongly temperature dependent relaxational excitation, observed at radio-microwave frequencies for the electric field parallel to the crystallographic a -axis, E || a is analyzed in detail. The temperature dependences of loss-peak frequency and dielectric strength of the excitation together with specific heat data confirm a ferroelectric order-disorder phase transition at T 0 ≈ 3 K in the network of H 2 O dipoles. Additional dielectric data are also provided for polarization E || b , too. Overall, these combined experimental investigations enable detailed conclusions concerning the dynamics of the confined water molecules that develop within their microscopic energy landscapes.
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