Proton Glass Research Articles

Guiding properties of proton-implanted Nd3+-doped phosphate glass waveguides**Project supported by the National Natural Science Foundation of China (Grant Nos. 11405041 and 61475189) and NUPTSF, China (Grant Nos. NY214159, NY215007, and NY215113).

We report on the fabrication and properties of an optical waveguide in Nd3+-doped phosphate glass. The planar waveguide was obtained by 550-keV proton implantation with a dose of . The proton–glass interaction was simulated by the stopping and range of ions in matter (SRIM software). The characteristics of the waveguide including the refractive index profile and the near-field intensity distribution were studied by the reflectivity calculation method and the end-face coupling technique. The optical waveguide demonstrated multi-mode behavior at the wavelength of 632.8 nm. The propagation features of the proton-implanted Nd3+-doped phosphate glass waveguide shows its potential to operate as an integrated photonic device.

Finite block pseudo-spin approach of proton glass

Abstract We herein propose an alternative phenomenology to explain the phase of proton glass by reference to finite block spin theory in magnetism, in which the phase may be considered as being a short-range ferroelectric ordering of block pseudo-spins comprised of random pseudo-spins that have a majority of individual pseudo-spins in a given sense. By making use of the Curie law of block pseudo-spins, we obtained the dielectric susceptibility for the lower and higher temperature approximations of the Brillouin function . The experimental results for the susceptibility in hydrogen-bonded mixed crystals of ferroelectric RbH 2 P(As)O 4 and antiferroelectric NH 4 H 2 P(As)O 4 were thus fitted fairly well at low temperatures in the proton glass phase whereas some deviation from our formulation was seen at high temperatures in the paraelectric phase.

Influence of varying hydrogen bond strength resulting from compositional variation on the vibration spectra of proton glasses: K1−x(NH4)xH2PO4

Single crystal neutron diffraction investigation [Choudhury and Chitra, J. Phys. Condense Matter, 25 (2013) 075902] on four mixed crystals with composition (K1−x(NH4)xH2PO4) where x=0.0, 0.29, 0.67, and 1.0 belonging to the potassium dihydrogen phosphate family of hydrogen bonded ferroelectric crystals had revealed that the compositional variation results in subtle structural differences primarily in the hydrogen bonds of these crystals. The study indicated that there is a change in hydrogen bond strengths with the change in crystal composition. Spectral investigation of the same set of four mixed crystals is undertaken with an intention to study the influence of the varying hydrogen bond strength on the vibrational properties of the crystals. Room temperature Raman spectra for all the four crystals are recorded in the range 100–4000cm−1. This Raman investigation correlates the structural changes observed from neutron diffraction investigations to the changes in the vibration spectra of the crystals. The varying N–H–O hydrogen bond strength in the mixed crystals is found to have an observable effect on the librational frequencies of the molecular components of these crystals. The strong OHO hydrogen bonds in these crystals give rise to four spectral bands in the 1500–3000cm−1 spectral region; this is in accordance with the theoretical prediction from the tunneling model for the very strong OHO hydrogen bonds. These OHO bonds can be described by a low barrier double well potential; the vibrational energy levels of the potential are split due to quantum tunneling effects. It is observed that the varying OHO hydrogen bond strength of these crystals results in a variation in the splitting of the vibrational energy levels of the hydrogen bond potential. It is attempted to correlate the varying OHO hydrogen bond strength with the expected variation in the freezing temperature with composition of these proton glasses.

Influence of N–H–O hydrogen bonds on the structure and properties of (K1−x(NH4)xH2PO4) proton glasses: a single crystal neutron diffraction study

It has been known for quite some time now that proton dynamics plays a key role in the structural ferroelectric (FE)/antiferroelectric (AFE) phase transition in the crystals belonging to the potassium dihydrogen phosphate crystal family. Mixed crystals belonging to this family having the composition M1−x(NW4)xW2AO4, where M = K, Rb, Cs, W = H, D, and A = P, As, exhibit proton glass behavior due to frustration between FE and AFE ordering; these proton glasses do not undergo any structural phase change but retain their room temperature structure down to very low temperatures. Single crystal neutron diffraction investigations of four mixed crystals with composition (K1−x(NH4)xH2PO4), where x = 0.0, 0.29, 0.67 1.0, were undertaken with the intention to investigate the effect of the local structural deviations on the overall average structure of the crystals and correlate these structural changes to the presence or absence of a structural phase transition in these crystals. Hydrogen bonding is shown to play a key role in the changing nature of the mixed crystals as the composition varies from the potassium rich ferroelectric region to the proton glass region to the ammonium rich antiferroelectric region.

Polysulfone/C30B Nanocomposite Membranes for Fuel Cell Applications: Effect of Various Sulfonating Agents

The effect of various sulfonating agents (Chlorosulfonic acid and Trimethylsilylchlorosulfonate (TMSCS) on the performance of Polysulfone (PSU) nanocomposite membranes was investigated. FTIR and 1H NMR results confirmed the sulfonation reaction. Sulfonation of PSU as well as incorporation of Cloisite 30B (C30B) as a filler, resulted in an increase of proton conductivity, water uptake and glass transition temperature (Tg). Thermogravimetric analysis (TGA) exhibited a decrease in decomposition temperature with sulfonation.XRD confirmed positive interaction between C30B and SPSU. Surface and cross-sectional morphology of the membranes were studied using SEM.

Robert Blinc

Robert Blinc

Coexistence of Antiferroelectric and Proton Glass States in Mixed K0,26(NH4)0.74H2PO4 Crystal Under Restricted Geometry Conditions

The dielectric response of K0,26(NH4)0.74H2PO4–SiO2 composite prepared by embedding of corresponded salts into porous SiO2 glass with 320 nm average pore diameter has been studied at the temperature range of 10–300 K. The transition from paraelectric to antiferroelectric (AFE) phase in implanted particles is detected at TN ≈ 45 K. Below ≈ 20 K the specific dispersion of dielectric response indicates a transition into proton glass (PG) state. It was found that the average time of dielectric relaxation follows the empirical Vogel—Fulcher law. Obtained results speak in favor of the coexistence of AFE and PG phases at low temperatures.

Thermodynamic and Dielectric Properties of K1−x(NH4)xH2PO4 Mixed Crystal

We used the cluster pseudospin model for the K1−x(NH4)xH2PO4 type proton glasses, which takes into account the energy levels of protons near a PO4 groups (within the cluster approximation), the long-range interactions between the hydrogen bonds, and an internal random deformation field. We obtained a qualitative description of the temperature behavior of the order parameters, static dielectric permittivity, and the phase diagram of the K1−x(NH4)xH2PO4 compounds.

Microscopic Theory of Rb1 - x(NH4)xH2PO4 Type Compounds

We propose a pseudospin model for the Rb 1 −x (NH 4 )xH 2 PO 4 type proton glasses, which takes into account energy levels of hydrogens near a PO 4 group (within a cluster approximation), long-range interactions between the hydrogen bonds, and an internal random deformational field. Relaxation is explored within the framework of the Glauber dynamics. We obtain a qualitative description of temperature behavior of the state parameters and dielectric permittivities of Rb 1 −x (ND 4 ) x D 2 PO 4 compounds at different frequencies.

Erratum: Quantum and Classical Relaxation in the Proton Glass [Phys. Rev. Lett.97, 145501 (2006)

Erratum: Quantum and Classical Relaxation in the Proton Glass [Phys. Rev. Lett.<b>97</b>, 145501 (2006)

2H NMR investigation of the transition to the proton glass state in the Cs5H3(SO4)4 · 0.5H2O crystal

A crystal of the Cs5H3(SO4)4 · xH2O (x ≈ 0.5) (PCHS) compound, which belongs to the family of proton conductors with a complex system of hydrogen bonds, is investigated by 2H NMR spectroscopy. The temperature and orientation dependences of the 2H NMR spectra are measured and analyzed. It is established that, upon transition to the glassy phase at the temperature T g = 260 K, the parameters characterizing the proton exchange between positions in hydrogen bonds remain unchanged to within the limits of experimental error. The protons in the two-dimensional network of hydrogen bonds in the (001) plane are dynamically disordered over possible positions down to temperatures considerably lower than the glass transition point T g . However, water molecules are fixed at particular structural positions in the phase transition range. In PCHS crystals with a nonstoichiometric water content, this circumstance can be responsible for the frustration that leads to the formation of the glassy state.

Quantum and Classical Relaxation in the Proton Glass

The hydrogen-bond network formed from a crystalline solution of ferroelectric RbH2PO4 and antiferroelectric NH4H2PO4 demonstrates glassy behavior, with proton tunneling the dominant mechanism for relaxation at low temperature. We characterize the dielectric response over seven decades of frequency and quantitatively fit the long-time relaxation by directly measuring the local potential energy landscape via neutron Compton scattering. The collective motion of protons rearranges the hydrogen bonds in the network. By analogy with vortex tunneling in superconductors, we relate the logarithmic decay of the polarization to the quantum-mechanical action.

FIR Spectra of [Ni(H2O)6](ClO4)2 and [Ni(D2O)6](ClO4)2 at Various Temperatures

Low frequency vibrations in [Ni(H2O)6](ClO4)2 and [Ni(D2O)6](ClO4)2 were measured by the FIR Fourier Transform Spectroscopy method. They were compared with those obtained by the IINS method. No evidence of proton glass discovered by the IINS was observed via the FIR method. By applying the band contour method, the barrier to rotation U act for H2O groups in [Ni(H2O)6](ClO4)2 crystals was determined. A III–II phase transition mechanism was proposed.

A glass‐like state in K4LiH3(SO4)4 crystal

AbstractResults of a dielectric study of one‐component single crystal K4LiH3(SO4)4 (KLHS) indicate the existence of a glass‐like state as a result of competing interactions between two types of hydrogen bonds. Thee calculated activation energy is similar to that reported for other proton glass crystals and the temperature dependence of the order parameter, obtained from the cluster theory, has confirmed the glassy behaviour of the KLHS. A directional dependence of the glass‐like behaviour has been studied showing that in the temperature range 18–100 K the glassy state exists only in the [100] direction. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Phases Coexistence of Hydrogen-Bonded K1 -x(NH4)xH2PO4 Crystal

The problem of proton-glass and ferroelectric phases coexistence in inhomogeneous ferroelectric K1 − x (NH4) x H2PO4 abbreviated KADP crystals based on dielectric studies up to temperature 0.3 K is presented. The measurements were performed in the helium-3 cryostat in the temperature range from 300 K to 0.3 K. Glass behavior for the KADP the proton glass occurs for a concentration x > 0.05. The partial phase diagram of KADP as a function of fractional ammonium concentration x and temperature T are presented.

Phase transitions and relaxation characteristics of Quantum Magnets and Quantum Glasses

An overview is presented of the phase changes as well as certain relaxation characteristics of model quantum magnets, magnetic glasses and proton glasses. Although the systems considered are quite varied, they are connected by the common themes of tunneling, transverse Ising model, long-ranged interactions and above all, the occurrence of quantum phase transitions. Because the interactions are long-ranged, mean-field theory is eminently suitable for analyzing both the equilibrium and nonequilibrium properties. Wherever pertinent, detailed comparisons with experimental data have been presented.

Phases Coexistence of Hydrogen-Bonded Mixed Ferroelectric and Antiferroelectric Crystals

The problem proton-glass and ferroelectric phases coexistence in Rb1−x (NH4) x H2AsO4 (RADA) and K1−x (NH4) x H2PO4 (KADP) crystals based on dielectric studies up to temperature 0.3 K is presented. The measurements were performed in the helium-3 cryostat in the temperature range from 300 K to 0.3 K. Glass behavior for the RADA is present even for a small concentration x = 0.01, whereas for the KADP the proton glass occurs for a concentration x > 0.05. The partial phase diagrams of RADP and KADP as a function of fractional ammonium concentration x and temperature T are presented.

Dielectric investigation of the temperature dependence of the dynamics of a hydrated protein

We have investigated the dielectric properties, as a function of frequency and temperature, of the hydrated globular protein lysozyme. A large data set made up by measurements performed with a conventional capacitance bridge and with a dielectric broadband apparatus on the same sample has allowed us to identify two dielectric dispersions. The main dispersion is due to migrating protons along hydrogen bonded water molecules adsorbed on the protein surface. The dynamics of these charges has many analogies with that of proton glasses and other glass forming materials. Remarkably, the proton glass transition temperature, Tg, coincides with the temperature indicating the onset of hydrogen bond network dynamics at the protein–water interface. On the other hand, the second dispersion does not show any glassy behavior; this is attributed to small scale motions of protein side chains triggered by solvent, thus providing compelling evidence of the interplay between hydration water and protein dynamics, with possible implication for catalytic activity.

Composition Effect on Glass-Like Properties of Mixed Crystals of KDP Type with Competing Interaction

The analysis of dielectric and polarization properties of mixed ferroantiferroelectric crystals (1 −x )KDP-xADP and related systems has been performed for broad range of concentration x. The problems concerning the composition effect on spontaneous polarization, diffuseness of phase transitions, dynamics of proton glass transition and phase coexistence are discussed.

Replica Symmetric Solutions of Random Field Tunneling Model for Proton Glasses

We investigate for the replica-symmetric solutions of the tunneling model proton glass with longitudinal random field of Gaussian distribution. From the replica-symmetric solutions we obtain phase diagrams for each random field distribution, especially the de Almeida-Thouless stability lines in the temperature ( T ) - average interaction strength ( J 0 ) plane and also in the temperature ( T ) - external longitudinal field ( H ) plane.