Using electron spin resonance spectroscopy (ESR), we measure the rotational mobility of probe molecules highly diluted in deeply supercooled bulk water and negligibly constrained by the possible ice fraction. The mobility increases above the putative glass transition temperature of water, T g ‫؍‬ 136 K, and smoothly connects to the thermodynamically stable region by traversing the so called ''no man's land'' (the range 150 -235 K), where it is believed that the homogeneous nucleation of ice suppresses the liquid water. Two coexisting fractions of the probe molecules are evidenced. The 2 fractions exhibit different mobility and fragility; the slower one is thermally activated (low fragility) and is larger at low temperatures below a fragile-to-strong dynamic cross-over at Ϸ225 K. The reorientation of the probe molecules decouples from the viscosity below decoupling of transport properties ͉ dynamic cross-over in water ͉ dynamic heterogeneity ͉ supercooled water ͉ polycrystalline materials T he physical properties of water are far from being completely understood. Several thermodynamic and dynamic anomalies are known or anticipated in the metastable supercooled regime that influence the equilibrium states and have deep impact in biology, astrophysics, glaciology, and atmospheric science (1-3). At ambient pressure, the supercooled regime ranges between the commonly accepted value of the glass transition temperature T g ϭ 136 K and the freezing temperature T m ϭ 273.15 K. Above T g , amorphous water transforms into a highly viscous fluid (4, 5). Crystallization into metastable cubic ice (I c ) at T X Ϸ 150 K with further transformation to the usual hexagonal form of ice I h is reported (1, 6). On the other hand, bulk water at atmospheric pressure can be supercooled below its melting temperature down to the homogeneous nucleation temperature T H Ϸ 235 K, below which it usually crystallizes to I h . Thus, the region between T X and T H is often regarded as a region where liquid water cannot be observed [''no man's land,'' NML (1)]. Nonetheless, the coexistence of crystals and deeply supercooled liquids was suspected almost 1 century ago for bulk systems (7). More recently, evidence that water and cubic ice coexist in thin films in the temperature range 140-210 K was reported (8-11). The existence of liquid water has been also shown experimentally in veins (or so-called triple junctions) of polycrystalline ice (12) that serve as interfacial reservoirs for impurities (13-15). The size of such reservoirs is thermodynamically defined by surface forces and also by the curvature of the surface (i.e., the Kelvin effect in veins) (11, 16). In pure ice, the reservoir size increases when approaching the melting point (17). Notably, recent simulations concluded that in polycrystalline materials grain boundaries exhibit the dynamics of glass-forming liquids (45).This background motivated us to investigate the coexistence of ice and supercooled water in large volumes in an attempt to characterize the dynamical properties of the li...

Three long-standing problems related to the physics of water, viz., the possibility of vitrifying bulk water by rapid quenching, its glass transition, and the supposed impossibility of obtaining supercooled water between 150 and 233 K, the so-called "no man's land" of its phase diagram, are studied using the highly sensitive technique of spin probe ESR. Our results suggest that water can indeed be vitrified by rapid quenching; it undergoes a glass transition at approximately 135 K, and the relaxation behavior studied using this method between 165 K and 233 K closely follows the predictions of the Adam-Gibbs model.

Combining experiments with first principles calculations, we show that site-specific doping of Mn into SrTiO 3 has a decisive influence on the dielectric properties of these doped systems. We find that phonon contributions to the dielectric constant invariably decrease sharply on doping at any site. However, a sizable, random dipolar contribution only for Mn at the Sr site arises from a strong off-centric displacement of Mn in spite of Mn being in a non-d 0 state; this leads to a large dielectric constant at higher temperatures and gives rise to a relaxor ferroelectric behavior at lower temperatures. We also investigate magnetic properties in detail and critically reevaluate the possibility of a true multi-glass state in such systems.

The structure of the hydrogen bond network is a key element for understanding water's thermodynamic and kinetic anomalies. While ambient water is strongly believed to be a uniform, continuous hydrogen-bonded liquid, there is growing consensus that supercooled water is better described in terms of distinct domains with either a low-density ice-like structure or a high-density disordered one. We evidenced two distinct rotational mobilities of probe molecules in interstitial supercooled water of polycrystalline ice [Banerjee D, et al. (2009) ESR evidence for 2 coexisting liquid phases in deeply supercooled bulk water. Proc Natl Acad Sci USA 106: 11448–11453]. Here we show that, by increasing the confinement of interstitial water, the mobility of probe molecules, surprisingly, increases. We argue that loose confinement allows the presence of ice-like regions in supercooled water, whereas a tighter confinement yields the suppression of this ordered fraction and leads to higher fluidity. Compelling evidence of the presence of ice-like regions is provided by the probe orientational entropy barrier which is set, through hydrogen bonding, by the configuration of the surrounding water molecules and yields a direct measure of the configurational entropy of the same. We find that, under loose confinement of supercooled water, the entropy barrier surmounted by the slower probe fraction exceeds that of equilibrium water by the melting entropy of ice, whereas no increase of the barrier is observed under stronger confinement. The lower limit of metastability of supercooled water is discussed.

In this paper we present the preparation and physical property studies on Pr0.7Pb0.3MnO3 (PPMO) nanoparticles with an average grain size of 5 nm. We find from SQUID magnetometry measurements that the Curie temperature (TC) remains unaltered at 205 K with decrease in the particle size down to 5 nm in comparison with bulk TC (200 K). From electron magnetic resonance (EMR) measurements, it is found that PPMO nanoparticles are more homogeneous than bulk PPMO. Only one EMR signal is observed down to 4 K in PPMO with an average particle size of 5 nm in contrast to the two EMR signal behaviour observed in bulk PPMO (200–240 K). The origin of the two EMR signals in the bulk was attributed to possible phase separation (Padmanabhan B et al 2007 Physica B 398 107). Such a phase separation is therefore concluded to be absent in nano-PPMO. In addition, temperature-dependent optical phonon measurements performed on 5 nm PPMO nanoparticles indicate the insulator–metal transition TMI = 230 K, which is nearly the same as that of the bulk sample (TMI = 235 K).