Structural transitions in ice samples at low temperatures and pressures

The structure of ice samples formed in the decay of a water impurity gel at temperatures above 4 K and atmospheric pressure has been examined. The X-ray diffraction analysis indicates that three phases coexist in the initial sample at temperatures of 85–110 K. These phases are amorphous ice occupying up to 30% of the sample volume, cubic-phase ice I _c metastable at low pressures (∼60%), and normal hexagonal ice I _h (≤6%). The characteristic sizes of crystals of the cubic and hexagonal phases are about 6 and 30 nm, respectively. The amorphous phase at annealing above 110 K is gradually transformed to the crystalline phase both cubic and hexagonal. This transition is accompanied by two processes, including a fast increase in the sizes of cubicphase nanocrystals and the partial transition of the cubic phase I _c to the hexagonal one I _h. Hexagonal ice I _h prevails in the bulk of the sample above 200 K.     

Crossover between the thermodynamic and nonequilibrium scenarios of structural transformations of H<Subscript>2</Subscript>O I<Emphasis Type="Italic">h</Emphasis> ice during compression

A detailed investigation of different scenarios of structural transformations of H₂O Ih ice during compression to a pressure of 2 GPa in the temperature range from 77 to 200 K is performed. In the range of temperatures and pressures being treated, detailed data are obtained for the density and the shear modulus for different phases of ice including the hda, IX, and XII phases. The experimentally obtained correlations for the density and ultrasonic velocities, with due regard for the available data of structural investigations, are used to identify the transformation sequences Ih→hda (below 135 K), Ih→II→VI (above 165 K), and Ih→IX→VI (from 155 to 180 K). In the vicinity of the crystallization temperature of amorphous ice, i.e., at about 140 K, an anomalous transformation pattern is observed, which is interpreted as predominantly the Ih→XII phase transition. The temperature crossover is discussed between the mode of solid-phase amorphization (Ih→hda) and crystal-crystal transitions, as well as the metastable nature of IX ice and the mechanism of solid-phase amorphization.     

Anomalies of the baric and temperature dependences of the elastic characteristics of ice during solid-phase amorphization and the phase transition in the amorphous state

The elastic characteristics of ice up to pressures of 1.7 GPa are determined for the first time at a temperature of 77 K, along with features of their variation associated with the phase transformation of hexagonal ice Ih into high-density amorphous ice hda. The elastic instability of the ice lattice before solid-phase amorphization is experimentally confirmed. Elastic instability during a transition from one amorphous state to another amorphous state was also observed for the first time; this took place when hda ice was warmed at p=0.05 GPa from T=77 K. Zh. éksp. Teor. Fiz. 112, 200–208 (July 1997)     

Dislocation mechanism for transformation between cubic ice Ic and hexagonal ice Ih

Cubic ice I_c is metastable, yet can form by the freezing of supercooled water, vapour deposition at low temperatures and by depressurizing high-pressure forms of ice. Its structure differs from that of common hexagonal ice I_h in the order its molecular layers are stacked. This stacking order, however, typically has considerable disorder; that is, not purely cubic, but alternating in hexagonal and cubic layers. In time, stacking-disordered ice gradually decreases in cubicity (fraction having cubic structure), transforming to hexagonal ice. But, how does this disorder originate and how does it transform to hexagonal ice? Here we use numerical data on dislocations in hexagonal ice I_h to show that (1) stacking-disordered ice (or I_c) can be viewed as fine-grained polycrystalline ice with a high density of extended dislocations, each a widely extended stacking fault bounded by partial dislocations, and (2) the transformation from ice I_c to I_h is caused by the reaction and motion of these partial dislocations. Moreover, the stacking disorder may be in either a higher stored energy state consisting of a sub-boundary network arrangement of partial dislocations bounding stacking faults, or a lower stored energy state consisting of a grain structure with a high density of stacking faults, but without bounding partial dislocations. Each state transforms to I_h differently, with a duration to fully transform that strongly depends on temperature and crystal grain size. The results are consistent with the observed transformation rates, transformation temperatures and wide range in heat of transformation.     

Ultrasonic study of solid-phase amorphization and polyamorphism in an H2O-D2O (1: 1) solid solution

The elastic moduli and volume of H₂O-D₂O (1: 1) isotopically mixed ice (solid solution) have been studied at the solid-phase amorphization of normal 1h ice under compression at a temperature of 77 K and at the transition from high-density amorphous ice to low-density amorphous ice with subsequent successive crystallization to cubic (1c) and hexagonal (1h) ice at isobaric (0.05 GPa) heating. Comparison of the results with the respective data for H₂O and D₂O ices indicates that the observed concentration (in the isotopic composition) dependences of the elastic moduli and their derivatives for different phases of ice at isotopic hydrogen substitution in the H₂O, H₂O-D₂O (1: 1), and D₂O chain can be both monotonic and significantly nonmonotonic.     

In situ Raman and optical microscopy of the relaxation behavior of amorphous ices under pressure

The transformation of low‐density amorphous (LDA) ice produced from high‐density amorphous (HDA) ice was studied up to 400 MPa as a function of temperature by in situ Raman spectroscopy and optical microscopy. Changes in these amorphous states of H₂O were directly tracked without using emulsions to just above the crystallization temperature T_x. The spectra show significant changes occurring above ∼125 K. The results are compared with data reported for the relaxation behavior of HDA, to form what we call relaxed HDA, or rHDA. We find a close connection with expanded HDA (eHDA), which is reported to exist as another metastable form in this P–T region. The observation of this temperature‐induced LDA transition under pressure complements the previously observed pressure‐induced reversible transition between LDA and HDA at 120–140 K. Copyright © 2009 John Wiley & Sons, Ltd.     

Elastic properties of D<Subscript>2</Subscript>O ices in solid-state amorphization and transformations between amorphous phases

Nonequilibrium phase transformations in D₂O ices, including the solid-state amorphization of ice 1h (1h-hda) and the heating-induced transition cascade hda-lda-1c-1h from high-density amorphous (hda) ice to low-density amorphous (lda) ice followed by crystallization in cubic ice 1c and phase transition to ordinary hexagonal ice 1h, were studied using an ultrasonic technique. It has been shown that, as in H₂O ice, the softening of a crystal lattice or an amorphous network precedes nonequilibrium transformations. However, noticeable isotopic differences in the behavior of the elastic properties of H₂O and D₂O, in particular, their 1h and hda modifications, call for a more detailed study of the structural features of these H₂O and D₂O phases.     

Raman spectra of proton order of thin ice Ih film

The polarized Raman spectra of the upper part of a thin ice Ih film were obtained in the range of 150 cm⁻¹ to 3800 cm⁻¹. The spectra showed clear polarization dependence; several new peaks were also observed. The longitudinaloptic–tranverseoptic (LO–TO) splitting of the mode near 220 cm⁻¹ in the translational vibration region was experimentally confirmed at 133 K. The Fermi resonance between the bending overtone (around 3270 cm⁻¹) and symmetry stretching fundamental (around 3350 cm⁻¹) in the stretching vibration region appeared at nearly the same temperature. Results showed that ice XI (i.e. proton‐ordered phase of ice Ih) slowly formed in the upper part of a thin ice Ih film without KOH as the temperature gradually decreased below 133 K. Copyright © 2015 John Wiley & Sons, Ltd.     

Formation and composition of the clathrate phase in the H<Subscript>2</Subscript>O-H<Subscript>2</Subscript> system at pressures to 1.8 kbar

The transition of the hexagonal ice phase I_h to the clathrate phase sII has been found in the H₂O-H₂ system at a pressure of about 1 kbar under conditions of an excess of gaseous hydrogen. The pressures of the I_h → sII and sII → I_h transitions have been determined over a temperature range from ?36 to ?18°C, and the pressure dependence of the synthesis temperature of the clathrate phase from a liquid at pressures from 1.0 to 1.8 kbar has been constructed. The solubility of hydrogen in the I_h and sII phases and in liquid water has been measured. The concentration of hydrogen in the clathrate phase sII is about 1.2 wt % (10 mol %) near the boundary of the sII → I_h transition, and it increases to 2 wt % (16 mol %) at a pressure of 1.8 kbar.     

Comparison of effect of 5 MeV proton and Co-60 gamma irradiation on silicon NPN rf power transistors and N–channel depletion MOSFETs

NPN transistors and N-channel depletion metal oxide semiconductor field effect transistors (MOSFETs) were irradiated with 5?MeV protons and ⁶⁰Co gamma radiation in the dose ranging from 1?Mrad(Si) to 100?Mrad(Si). The different electrical characteristics of the NPN transistor such as Gummel characteristics, excess base current (ΔI_B), dc current gain (h_FE), transconductance (g_m), displacement damage factor (K) and output characteristics were studied as a function of total dose. The different electrical characteristics of N-channel MOSFETs such as threshold voltage (V_th), density of interface trapped charges (ΔN_it), density of oxide trapped charges (ΔN_ot), transconductance (g_m), mobility (µ) and drain saturation current (I_DSat) were studied systematically before and after irradiation in the same dose ranges. A considerable increase in the base current (I_B) and decrease in the h_FE, g_m and collector saturation current (I_CSat) were observed after irradiation in the case of the NPN transistor. In the N-channel MOSFETs, the ΔN_it and ΔN_ot were found to increase and V_th, g_m, µ and I_DSat were found to decrease with increase in the radiation dose. The 5?MeV proton irradiation results of both the NPN transistor and N-channel MOSFETs were compared with ⁶⁰Co gamma-irradiated devices in the same dose ranges. It was observed that the degradation in 5?MeV proton-irradiated devices is more when compared with the ⁶⁰Co gamma-irradiated devices at higher total doses.     

Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice

The hydrogen mean force from experimental neutron Compton profiles is derived using deep inelastic neutron scattering on amorphous and polycrystalline ice. The formalism of mean force is extended to probe its sensitivity to anharmonicity in the hydrogen-nucleus effective potential. The shape of the mean force for amorphous and polycrystalline ice is primarily determined by the anisotropy of the underlying quasi-harmonic effective potential. The data from amorphous ice show an additional curvature reflecting the more pronounced anharmonicity of the effective potential with respect to that of ice Ih.     

An analysis of 175 MeV Nickel ion irradiation and annealing effects on silicon NPN rf power transistors

In this study NPN rf power transistors were irradiated by 175 MeV Ni¹³⁺ ions in the dose range of 100 krad to 100 Mrad. Their characteristics such as excess base current (ΔI_B = I_Bpost ? I_Bpre), dc current gain (h_FE), transconductance (g_m) and collector-saturation current (I_CSat) were studied before and after irradiation. The damage factor (K) for h_FE was calculated using Messenger–Spratt relation. The base current (I_B) was found to increase significantly after irradiation and in turn decreases the h_FE. The g_m and collector current (I_C) in the saturation region (I_CSat) were found to decrease with increase in radiation dose. The results obtained here were also compared with that obtained by 140 MeV Si¹⁰⁺ ions, 100 MeV F⁸⁺ ions, 95 MeV O⁷⁺ ions and 50 MeV Li³⁺ ions irradiation studies in the same dose ranges to understand the LET effects. The recovery in the I–V characteristics of irradiated NPN transistors were studied by isothermal and isochronal annealing methods.     

Structural,optical and electrical properties of laser irradiated Pb doped Ga–Se chalcogenide thin films

Using the Transverse Electrical Excitation at Atmospheric Pressure (TEA) nitrogen laser, we had irradiated the amorphous thin films of Ga₁₀Se₈₁Pb₉ chalcogenide glass and the results have been discussed in terms of the structural aspects of Ga₁₀Se₈₁Pb₉ glass. The observed changes are associated with the interaction of the incident photon and the lone-pairs electrons which affects the band gap. The X-ray structural characterization revealed the amorphous nature of as prepared films and polycrystalline nature of the laser irradiated films. The optical band gap of these thin films is measured by using the absorption spectra as a function of photon energy in the wavelength region 400–1200 nm. It is found that the optical band gap decreases while the absorption coefficient increases with increasing the irradiation time. The decrease in the optical band gap has been explained on the basis of change in nature of films, from amorphous to polycrystalline state, with the increase in exposure time. The dc conductivities and activation energies of these thin films are measured in temperature range 303–403 K. It has been found that the activation energy in Ga₁₀Se₈₁Pb₉ chalcogenide thin films decreases whereas the dc conductivity increases at each temperature by increasing the irradiation time.     

Positron lifetime measurements on electron irradiation damage in amorphous Pd80Si20 and Cu50Ti50 alloys

Positron lifetime measurements were performed on amorphous Pd₈₀Si₂₀ and Cu₅₀Ti₅₀ alloys irradiated with 3MeV electrons at 20K. The irradiation was found to increase the mean positron lifetime in both specimens indicating the presence of vacancy-like radiation damage. Isochronal annealing between 77 K and 300 K resulted in a continuous reduction of the positron lifetime, which suggests a gradual recovery of the irradiation induced defects.     

The effects of high-energy ion irradiations on the I–V characteristics of silicon NPN transistors

The silicon NPN rf power transistors were irradiated with different linear energy transfer (LET) ions such as 50?MeV Li³⁺, 80?MeV C⁶⁺ and 150?MeV Ag¹²⁺ ions in the dose range of 1–100?Mrad. The SRIM simulation was used to understand the energy loss and range of these ions in the transistor structure. The different electrical parameters such as Gummel characteristics, excess base current (ΔI_B), DC current gain (h_FE), displacement damage factor (K) and output characteristics were systematically studied before and after irradiation. The ion irradiation results were compared with ⁶⁰Co-gamma irradiation result in the same dose range. A considerable increase in base current (I_B) and a decrease in h_FE and I_CSat were observed after irradiation. The degradation in the electrical parameters was comparably very high for Ag¹²⁺ ion-irradiated transistor when compared to other ion-irradiated transistors, whereas the degradation in the electrical parameters for Li³⁺ and C⁶⁺ ion-irradiated transistors was comparable with gamma-irradiated transistor. The isochronal annealing study was conducted on the 100?Mrad irradiated transistors up to 500°C to analyze the recovery in different electrical parameters. The h_FE and other electrical parameters of irradiated transistors were almost recovered after 500°C for 50?MeV Li³⁺, 80?MeV C⁶⁺ ion and ⁶⁰Co-gamma-irradiated transistors, whereas for 150?MeV Ag¹²⁺ ion-irradiated transistor, the recovery in electrical characteristics is not complete.     

Monolayer structure for some dissociatively adsorbed molecules and molecular H2O on noble and transition metal surfaces

The model of neighbour site blockage for atomic adsorption on noble and transition metal surfaces predicts monolayer structures quite successfully. For molecularly adsorbed water, the assumption that the molecular separation in the monolayer is that in the basal plane of bulk I_h ice predicts the majority of known monolayer structures.     

Mössbauer study of ferromagnetic metallic glasses irradiated by swift heavy ions at temperatures 100 and 300 K

The effect of swift heavy ion irradiation on ferromagnetic metallic glasses Fe₄₀Ni₃₈Mo₄B₁₈ and Fe₇₈Si₉B₁₃ has been studied. The ion beams used are 100 MeV ¹²⁷I and 180 MeV ¹⁹⁷Au. The specimens were irradiated at fluences ranging from 3 × 10¹² to 1.5 × 10¹⁴ ions/cm². The irradiations have been carried out at temperatures 100 and 300 K. The magnetic moments are sensitive towards the irradiation conditions such as irradiation temperature and stopping power of incident ion beam. The irradiation-induced effects have been monitored, by using Mössbauer spectroscopy. The modifications in magnetic anisotropy and hyperfine magnetic field distributions, as an effect of different irradiation temperature as well as different stopping power have been discussed. After irradiation, all the samples remain amorphous and magnetic anisotropy considerably changes from its original in-plane direction. The results show enhancement in magnetic anisotropy in the specimen irradiated at 100 K, as compared to that of irradiated at 300 K. It is expected that at low temperature, the stresses produced in the material would remain un-annealed, compared to the samples irradiated at room temperature and therefore, the modification in magnetic anisotropy would be enhanced. A distribution of hyperfine magnetic field, of the samples irradiated at low temperature, show a small but distinct peak at ～?11 Tesla, indicating Fe-B pairing.     

Thermoluminescence and photoluminescence characteristics of K2YF5: Tb3++PTFE irradiated with 90Sr/90Y beta particles

This article presents results of thermoluminescence (TL) and photoluminescence (PL) measurements performed on beta-irradiated K ₂YF ₅:Tb ³⁺+PTFE pellets. K ₂YF ₅ crystals doped with 0.1% of trivalent optically active Tb ³⁺ ions in pellets form were investigated. The TL glow curve of K ₂YF ₅:Tb ³⁺+PTFE has a simple structure with two well-defined peaks centered at 170 and 307 °C. The TL sensitivity of the K ₂YF ₅:Tb ³⁺+PTFE irradiated with beta radiation was found to be higher than that of commercial phosphor TLD-100 (LiF:Mg,Ti), at the same conditions of irradiation and readout. Moreover, PL measurements performed on the terbium doped material show the presence of Terbium as Tb ³⁺ in the material.     

Annealing of vacancies in electron-irradiated α-iron

Positron lifetime studies are reported on the behaviour of vacancies in high-purity electron irradiated α-iron. Results show that already at temperatures around 220 K vacancies migrate and form agglomerates, which anneal out only well above room temperature. The decrease of monovacancy concentration at stage I_E around 130 K is also visible.     

Calorimetric study of proton ordering in hexagonal ice catalyzed by hydrogen fluoride

Heat capacities of hexagonal ices doped with 2.6, 26 and 260 m mol dm^?3 HF were measured with an adiabatic calorimeter. The HF doping accelerated proton ordering which has been known to take place sluggishly around 100 K. The ice containing 26 m mol dm^?3 HF showed the largest excess entropy ((0.102±0.01) J K^?1 mol^?1) and the shortest relaxation time. The relaxation time at 90 K was about $\text{1}\text{30}$ of that of the pure ice I_h at the same temperature. The activation enthalpies obtained were the same for all of the doped ices, (23.5±2.0) J mol^?1, which is approximately equal to the activation energy of the mobility of the Bjerrum L-defect.