Experimental evidence of the ferroelectric nature of the $\lambda$-point transition in liquid water

We studied the dielectric properties of nano-sized liquid water samples confined in polymerized silicates MCM-41 characterized by pore sizes $3$–$10$ nm. Freezing temperature suppression in nanopores helps keep the water samples in liquid form at temperatures well below $0\,^{\circ}$C and thus effectively study the properties of supercooled liquid water. We report the first direct measurements of the dielectric constant by the dielectric spectroscopy method and demonstrate very clear signatures of the second-order phase transition of ferroelectric nature at temperatures next to the $\lambda$-point in the supercooled bulk water in full agreement with the recently developed model of the polar liquid.