Lithium Hydrazinium Sulfate Research Articles

Absence of critical exponents in ferroelectrics: experiments of Hilczer and theory of Levanyuk and Sigov

The pioneering breakthrough of Bozena Hilczer and her coworkers showed that the so-called critical phenomena in many ferroelectric crystals are entirely produced by defects. She studied gadolinium aluminum sulphate hexahydrate (GASH), lithium ammonium sulphate, lithium hydrazinium sulphate, PZT, barium titanate, and especially TGS, via neutron irradiation, X-ray irradiation, and e-beam electron irradiation, which showed that the divergences in specific heat or dielectric constant near the Curie temperature Tc are not caused by ‘critical’ fluctuations but by static defects, which can be annealed out and subsequently reproduced by irradiation. This work is rarely cited (modern physicists often feel that literature searches are optional), leading to frequent rediscovery and generally spurious claims of true ‘critical’ phenomena near Tc.

Macromol. Chem. Phys. 12/2010

Back Cover: The cover illustrates proton conductive polybenzimidazole (PBI) membranes containing lithium hydrazinium sulfate (LiHzS). The proton conductivity of the composite membranes increases with increasing content of LiHzS, and their mechanical properties indicate the composites have the mechanical stability that is suitable for high-temperature fuel cell membranes. Further details can be found in the article by J.-W. Jung, S.-K. Kim, and J.-C. Lee* on page 1322.

Temperature variation of the molecular structure of lithium hydrazinium sulphate—a one-dimensional proton conductor

The paper reports the results of detailed studies of the molecular structure of lithium hydrazinium sulphate single crystal in a wide temperature range with the aim to clarify previously reported anomalies in the molecular dynamics at ∼100 K. The crystal does not undergo any structural phase transition from 8 to 460 K however, the donor-acceptor distance, between the nitrogen atoms involved in the hydrogen bond along the c -orthorhombic axis, starts to increase from the temperature of ∼100 K. This results in an anomaly of the phase memory time observed in electron spin echo studies and anomalies of hydrazinium internal modes observed in Raman scattering. Moreover, the anisotropy of the SO 4 tetrahedra is maximal at ∼100 K and decreases at higher temperatures. The possible contribution of fast proton transport, described by the Grotthuss model, to the proton conductivity along the c -axis at the temperature above ∼400 K is discussed.

Low temperature dynamics of hydrazinium ions in lithium hydrazinium sulphate (LHS) studied by electron spin echo (ESE) technique

The temperature dependence of the phase memory time T M in γ-irradiated lithium hydrazinium sulphate, LiN 2H 5SO 4, single crystal has been measured in the temperature range 4.2–290 K. Two minima in T M( T) at 115 and 175 K were observed. The low-temperature T M minimum has been identified as due to librational motions of the N 2H 5 + hydrazinium ion with an activation energy of 0.045 eV. The T M minimum at 175 K has been assigned to rotation of the –NH 3 + end of the hydrazinium ion with an activation energy of 0.074 eV. The activation energies have been compared with the results of a previous NMR and Raman spectroscopic studies of this crystal.

Crystal Structure and Electrical Conductivity of LiN2H5SO4 at High Temperature

Electrical conductivity, differential scanning calorimetry and X-ray diffraction measurements have been performed on a single crystal of lithium hydrazinium sulfate, LiN2H5SO4, in the temperature range from 295 K to about 470 K. The crystal structures at several temperatures are determined in this temperature range. The structural phase transition is not found, but an abnormal decrease of the electrical conductivity with increasing temperature above 445 K is observed. The relation between the electric properties and the crystal structures of the sample crystal is discussed. The LiN2H5SO4 crystals are suggested to be proton and Li ionic conductors.

Elastic constants and high-temperature elastic anomalies near 425 K in lithium hydrazinium sulfate

All the nine elastic constants of the orthorhombic crystal lithium hydrazinium sulfate, Li(N2H5)SO4, have been determined by measuring ultrasonic velocities using pulse echo overlap technique at 10 MHz. Temperature variation of all the six diagonal elastic constants and the three off-diagonal combinations have been measured between 300 and 450 K. Some of the constants show anomalous behavior in the 410–440 K temperature region, which is attributed to a phase transition in the crystal near 425 K. Magnitude of the velocity anomaly is comparatively small. A new high-temperature ultrasonic bond material suitable for transverse waves is also reported.

X-ray diffraction study of lithium hydrazinium sulfate and lithium ammonium sulfate crystals under a static electric field

X-ray diffraction studies are made on proton conducting polar lithium hydrazinium sulfate and ferroelectric lithium ammonium sulfate. The X-ray rocking curves recorded with in situ electric field along the polar b axis of lithium hydrazinium sulfate (direction of proton conductivity) show a strong enhancement of the 0k0 diffraction intensity. The corresponding 0k0 X-ray topographs reveal extinction contrast consisting of striations parallel to the polar axis. They disappear when the electric field is switched off. The effect is very strong in 0k0 but invisible in h0l reflections. It is present only if the electric field is parallel to the polar axis b. This unusual X-ray topographic contrast is correlated with the proton conduction. It is supposed that, under electric field, an inhomogeneous charge distribution develops, distorting the crystal lattice. Similar experiments on lithium ammonium sulfate also show contrast variations, but of quite different behaviour than before. In this case they result from changes of the ferroelectric domain configuration under electric field.

Anomalous temperature-dependent Raman scattering in lithium hydrazinium sulfate

Results of a polarized Raman scattering study of single crystal lithium hydrazinium sulfate, LiN2H5SO4, over a temperature interval from 11 to 300 K are discussed. Unusual temperature dependence of the band center scattering intensity is observed in a few intramolecular hydrazinium modes, intramolecular sulfate ion modes, and lattice modes. The intensity of these modes increases with increasing temperature from 11 K to about 175 K, then abruptly decreases over a small interval between 175 and 200 K. Above 200 K the band center intensity then exhibits normal behavior, slowly decreasing with increasing temperature. Possible explanations for this anomalous behavior are discussed. Key words: lithium hydrazinium sulfate, proton conductor, Raman spectroscopy.

Hydrazinium ion vibrational motion and proton transport in lithium hydrazinium sulfate

Polarized Raman scattering spectra are measured over a temperature interval from 15 to 300 K in single crystal lithium hydrazinium sulfate. No unusual temperature-dependent behavior is observed in any mode involving hydrazinium ion translatory motion, but all librational modes and the internal mode markedly decrease in intensity and frequency, while significantly broadening. An analysis of the bandwidth and frequency data allows assignment of these modes to librations either perpendicular to or parallel to the internuclear axis.

Proton injection studies in lithium hydrazinium sulfate

A novel technique for studying the basic mechanism of proton transport in hydrogen-containing solids is described. In this technique, which is termed “proton injection”, the hydrogen-containing material (here, lithium hydrazinium sulfate) is utilized as the electrolyte in an electrochemical cell. Deuterium ions (or deuterons, D+) are produced from deuterium gas present at the anode and injected into the crystal. The subsequent diffusion of deuterium into the bulk material is followed by Raman spectroscopy.

Vibrational spectroscopic analysis of lithium hydrazinium sulfate

The low temperature polarized Raman spectra of lithium hydrazinium sulfate, LiN 2H 5SO 4, have been measured in the range 5–3500 cm −1. The symmetry-based assignments for the observed modes are given. The room temperature polarized i.r. reflectivity spectra in the range 200–4000 cm −1 were also measured to verify the presence of extensive TO—LO splitting in the sulfate ion ν 3 and ν 4 internal optic modes. In the lattice mode region, the lithium ion external optic modes are identified, and the spectra of the deuterated analog allow the identification of several modes due primarily to the external motions of either the sulfate or hydrazinium ions. Other lattice modes are found to be a mixture of sulfate and hydrazinium ion external motions. Coupling of the sulfate ion ν 3 modes and the hydrazinium ion group bending modes prevents an unambiguous assignment of the bands in the 1050–1200 cm −1 spectral region. The N—H stretching region spectra contain a larger number of modes than predicted by a factor group analysis. These extra modes are discussed in terms of resonance interactions of the N—H stretching fundamental modes with overtones and combination modes.

Electron spin resonance and optical absorption studies on copper-doped lithium hydrazinium sulphate single crystals

ESR and optical absorption studies have been carried out on Cu2+-doped lithium hydrazinium sulphate single crystals at 303 K. The spin-Hamiltonian parameters evaluated indicate a N2O2 square planar environment for Cu2+ ion in this lattice. The correlation ofESR and crystal structure data leads us to conclude that Cu2+ ion enters the lattice interstitially. Charge compensation is achieved by the release of protons. Using the optical absorption andESR data, bonding parameters and orbital reduction factors are also evaluated.

Raman spectroscopic studies of the fast proton conductor lithium hydrazinium sulfate

The temperature dependence of several low frequency external modes of lithium hydrazinium sulfate have been examined. The temperature dependent bandwidth and frequency of the 53 cm −1 mode have been studied over the temperature range 11–300 K. The significance of breaks observed in plots of spectral parameters vs. temperature for this mode are discussed.

Investigation of proton-conducting solids

One-dimensional bulk proton conduction parallel to the c axis was observed in solid lithium hydrazinium sulfate, LiN 2H 5SO 4. The conductivity in this direction is 2 × 10 −8 ω −1 cm −1 at 25°C and shows an activation enthalpy of 0.75 ± 0.07 eV. The two-dimensional conductors HUO 2AsO 4·4H 2O and HUO 2PO 4·4H 2O were studied as a function of their water content. The conductivities are 8 × 10 −6 and 3 × 10 −5 ω −1 cm −1 in the orthorhombic phase at −10°C, with activation enthalpies of 0.70 ± 0.05 and 0.57 ± 0.07 eV, respectively. Indications of peritectic transitions to the tetragonal phases were observed in the temperature ranges 15 to 47 and −5 to 10°C, respectively. The transition depends on the water content which appears to control the increase in conductivity in this material. The dependence upon various sample parameters is discussed. Fast proton transport in solids is proposed to occur by a “vehicle mechanism”, i.e. the motion of N 2H + 5, H 3O +- or other proton-containing groups.

A refinement of the crystal structure of lithium hydrazinium sulphate by X-ray diffraction

A refinement of the crystal structure of lithium hydrazinium sulphate by X-ray diffraction

Nitrogen-14 Nuclear Quadrupole Resonance Study of Lithium Hydrazinium Sulfate

Nitrogen-14 nuclear quadrupole resonance (NQR) transition frequencies of the NH2 group of the hydrazinium ion in lithium hydrazinium sulfate have been measured as a function of temperature from 4.2 to 360°K. The usual treatment of temperature dependence, which considers the effect on the transition frequencies of molecular oscillations about the principal field gradient axes, is generalized by considering oscillations about an arbitrarily oriented axis system. This generalization leads to the determination of the orientation of the field gradient axes in the NH2 group, and to a clarification of the existing model of the dynamics of the hydrazinium ion. It is found that between 40 and 320°K the NH2 group undergoes small oscillations about the N–N axis whose amplitude increases linearly with temperature. Above 320°K the amplitude of these oscillations increases more rapidly than a linear function. It is also found that above 150°K, proton exchange in the H–N–H plane of the NH2 group takes place rather than rigid rotation of the protons about the bisector of the H–N–H angle. The linear increase of oscillation amplitude with temperature between 40 and 320°K is found to be inconsistent with the Bayer theory, unless and ad hoc assumption is made about the temperature dependence of the oscillation frequencies.

Dielectric Properties of Lithium Hydrazinium Sulfate

The dc conductivity and ac dielectric susceptibility of normal and deuterated lithium hydrazinium sulfate have been measured over a wide temperature range at frequencies up to 9.33 GHz. Over a very large temperature and frequency range the real and imaginary parts of the susceptibility are very large (up to ${\ensuremath{\epsilon}}^{\ensuremath{'}}\ensuremath{\simeq}{\ensuremath{\epsilon}}^{\ensuremath{'}\ensuremath{'}}\ensuremath{\simeq}{10}^{6}$) and vary with frequency somewhat as ${f}^{\ensuremath{-}\frac{1}{2}}$. This unusual behavior is shown to result form the nearly one-dimensional protonic conductivity and its extreme sensitivity to barriers caused by local structural defects. Etching studies indicate that the crystal is not ferroelectric, implying that the apparent hysteresis loops result from saturation of the ac conduction.

Proton Rotating Frame Relaxation in Lithium Hydrazinium Sulfate, Li(N2H5)SO4

The temperature dependence of the rotating frame relaxation time T1ρ for protons in powdered lithium hydrazinium sulfate, Li(N2H5)SO4, has been determined from 140 to 495 °K. These measurements indicate that the –NH2 part of the N2H5+ ion executes 180° flips about the bisectrix of the H–N–H angle with activation energy of 10.7 ± 0.5 kcal/mole. Evidence for motion of the entire N2H5+ ion with activation energy of 17.4 ± 1.1 kcal/mole was also obtained. Separate reorientation and diffusion motions of the N2H5+ ion could not be distinguished, although evidence that the N2H5+ motion detected in the T1ρ measurements includes diffusion is obtained by comparing the T1ρ results with the temperature dependence of the proton second moment.

MOLECULAR REORIENTATION IN FERROELECTRIC LITHIUM HYDRAZINIUM SULPHATE

The temperature dependence of the spin-lattice relaxation time T1 and of the second moment of the magnetic-resonance absorption signal has been determined for protons in powdered lithium hydrazinium sulphate over the range 80–480 °K. These measurements indicate that the hydrazinium ion is rigid only at very low temperatures. As the temperature is raised, the −NH3 group begins to undergo hindered rotation about the N–N axis with an activation energy of 4.2 kcal/mole and the effect of this motion on the line width becomes pronounced in the region of 85 °K. Further molecular reorientation begins above room temperature and is probably reorientation of the −NH2 group about either the N–N axis or the bisectrix of the H–N–H angle. Above 435 °K the hydrazinium ion begins to tumble about several axes and at 480 °K diffuses through the structure.

A neutron diffraction study of the crystal structure of lithium hydrazinium sulphate

A neutron diffraction study of the crystal structure of lithium hydrazinium sulphate