Preliminary Broadband Dielectric Spectroscopy Insight into Compressed Orientationally Disordered Crystal-Forming Neopentyl Glycol (NPG)

This report presents the first results on broadband dielectric spectroscopy insights into ODIC-forming neopentyl glycol (NPG) under compression up to the GPa domain. Particular attention was paid to the strongly discontinuous phase transition: orientationally disordered crystal (ODIC)–solid crystal. The insights cover static, dynamic, and energy-related properties, namely evolutions of the dielectric constant, DC electric conductivity, and dissipation factor. Worth stressing are results regarding the pressure-related Mossotti catastrophe-type behavior of the dielectric constant, the novel approach to non-Barus dynamics, and the discussion on fundamentals of dissipation factor changes in NPG. The results presented in the given report also introduce new experimental evidence and model discussions regarding the nature of ODIC mesophase and discontinuous phase transitions. Notable is the significance of understanding the nature of the colossal barocaloric effect in NPG.The names of the individual files correspond to the numbering of the figures in the paper: Drozd-Rzoska, A.; Kalabiński, J.; Rzoska, S.J. Preliminary Broadband Dielectric Spectroscopy Insight into Compressed Orientationally Disordered Crystal-Forming Neopentyl Glycol (NPG). Materials2025, 18, 635. https://doi.org/10.3390/ma18030635Files included in this collection:Figure 2.txt - Example of the real part of the dielectric permittivity spectrum obtained in high-pressure studies in NPG, for 𝑇=50 °CFigure 3.txt - Example of the imaginary part of the dielectric permittivity spectrum obtained in high-pressure studies in NPG, for 𝑇=50 °CFigure 4.txt - Frequency changes of the real part of dielectric permittivity reciprocal for the selected pressures in the ODIC and crystal phasesFigure 5.txt - Isothermal (𝑇=50 °C) pressure dependence of the dielectric constant in NPG, in the surrounding of the ODIC—solid crystal transitionFigure 6.txt - The real part of the electric conductivity spectraFigure 7.txt - Pressure changes in electric conductivity in the ODIC and solid crystal phases of NPG, for a set of frequenciesFigure 8.txt - The pressure evolution of the dissipation factorFigure 9.txt - Frequency changes of the dissipation factor 𝐷(𝑓)=𝑡𝑎𝑛𝛿(𝑓)=𝜀″/𝜀′ in neopentyl glycol (NPG), for selected pressuresFigure 10.txt - Pressure-related evolution of the reciprocal of dielectric susceptibility 𝜒=𝜀−1, for the isotherm 𝑇=110 °C, where the ODIC phase is extended up to 𝑃~1.2 GPaFigure 11.txt - Pressure evolution of DC electric conductivity for the isotherm 𝑇=110 °C, where the ODIC phase is extended up to 𝑃~1.2 GPaFigure 12.txt - Apparent activation volume pressure changes for the isotherm 𝑇=110 °CFigure 13.txt - The ODIC–crystal discontinuous phase transition pressure dependence up to GPa domain