Internal friction of mixed alkali metaphosphate glasses: (II). Discussion

The internal friction and dielectric losses of mixed LiNa, LiK, LiCs, LiAg, NaK, NaCs and NaAg metaphosphate glasses are interpreted on the basis of explanation proposed for the mixed alkali effect. It was found that the magnitude of the mixed peak correlates better with size differences than with mass differences. The intermediate temperature peak is treated as a mixed proton-alkali peak. The large mechanical loss peak, appearing when the alkalis are mixed, was attributed to a coupled movement of dissimilar alkali ions and an explanation of the nature of this coupling is proposed. From this model it is predicted that mixed peaks can occur in any electrically insulating material containing dissimilar charge carriers.     

Internal friction of mixed alkali metaphosphate glasses: (I). Results

The internal friction of LiNa, LiK, LiCs, LiAg, NaCs and NaAg metaphosphate glasses was measured at 0.5 Hz and 2 kHz. The dielectric losses were also measured from 40 to 160°C, at frequencies of 300, 3 000 and 30 000 Hz. The densities of the glasses were determined and the molar volume of oxygen was calculated. In general, the mixed alkali behaviour of metaphosphate glasses is very similar to the mixed alkali behaviour of silicate glasses. Silver behaves in this respect like an alkali ion with approximately the same size as a sodium ion.     

Internal friction and dynamic modulus of metaphosphate glass

Internal friction and dynamic modulus were measured by a forced torsional vibration method at 0.5-5 Hz in the range of −120 to 300 °C for four kinds of metaphosphate glasses, 50MgO · 50P₂O₅(MgP), 48SrO · 52 P₂O₅(SrP), 25MgO · 25SrO · 50P₂O₅(MgSrP) and 25Na₂O · 25MgO · 50P₂O₅(NaMgP). Three internal friction peaks appeared for MgP at ∼−30, ∼105 and ∼230 °C, and the activation energies of the relaxation behavior obtained from the low, intermediate and high temperature regions were ∼110, ∼250 and ∼580 kJ/mol, respectively. For SrP, those three peaks were also obtained at ∼−45, ∼60 and ∼195 °C, and the activation energies were estimated as ∼95, ∼200 and ∼600 kJ/mol at each temperature, respectively. Two peaks appeared at ∼−50 and ∼160 °C for MgSrP, and ∼−55 and ∼70 °C for NaMgP, respectively. The obtained activation energies were ∼100 and ∼180 kJ/mol for MgSrP, and ∼75 and ∼200 kJ/mol for NaMgP, respectively. It is assumed that the primary peaks (the low temperature region) were influenced by the behavior of Mg²⁺, Sr²⁺ and Na¹⁺ ions, and the secondary peaks (the intermediate temperature region) were based on non-bridging oxygen associated with Mg²⁺, Sr²⁺ and Na¹⁺ ions. Dynamic modulus showed a decreased gradually with increasing temperature in the present temperature range for all the compositions.     

Internal friction of alkaline-earth-iron-metaphosphate glasses

The internal frictions of Mg, Ca, Ba iron-metaphosphate glasses were studied from 120 to 700 K using the low-frequency torsion pendulum technique. The internal friction as a function of temperature revealed two distinct peaks. The low-temperature peak was absent in glass without iron oxide. Its activation energy compared favourably with that for dielectric loss and dc conductivity in similar glasses. This suggests the same mechanism for all three processes, probably connected with electron transfer between iron ions of different valence.     

Internal friction in phosphoaluminate and borate glasses

Internal friction in sodium phosphoaluminate and borate glasses was investigated by torsion pendulum, beam vibration and pulse-echo methods. The Arrhenian relationship was verified in a frequency interval covering eight decades. A detailed analysis of the first peak was made to obtain the distribution of relaxation times and the distribution of activation entropy ΔS and activation enthalpy ΔH. The log-normal distributions were further compared to the Doremus theory and the observed discrepancy discussed.     

The influence of dissolved water on the internal friction of lithium metaphosphate glasses containing 1% potassium metaphosphate

A series of lithium metaphosphate glasses, containing different amounts of water, was prepared. The water content was determined from the weight-loss of specimens during heating in vacuum.It is found that dissolved water influences the internal friction and dielectric losses, in the same way as additions of dissimilar alkali ions do. With respect to the physical properties under discussions, one can consider water as an ‘alkali-oxide’.The intermediate temperature peak is increased in magnitude and shifted to lower temperatures with increasing water content. Extrapolation of the present results to the water-free composition shows that the intermediate temperature peak will be absent in the water-free glass.     

Internal friction of sodium phosphate glasses

The internal friction of XNa₂O·(1 ? X)P₂O₅ glasses, X varied from 0.29 to 0.59, has been measured from ?100 to +300°C at ～ Hz and from 25 to 300°C at ～ 2000 Hz. Two internal friction peaks were observed. Based on the compositional dependence of the low temperature peak and the agreement between the activation energy of this peak with that calculated from dielectric loss measurements, this peak was assigned to the stress induced movement of the sodium ions. The magnitude of the second peak occurring at higher temperature, in addition to varying with the sodium content, was also very sensitive to the water content; its magnitude increasing with increasing water content. This peak was concluded to be a type of ‘mixed alkali’ peak involving the cooperative movement of sodium ions and protons. Due to the shift of the background damping to lower temperatures with decreasing sodium content, neither peak could be observed for X < 0.30.     

The influence of dissolved heavy water on the internal friction of lithium metaphosphate glasses containing 1% potassium metaphosphate

A batch of very dry lithium metaphosphate glass, containing 1% potassium metaphosphate, was prepared and dissolved completely in nearly pure heavy water. From this solution, a series of glasses with varying deuterium oxide content was prepared. The internal friction and dielectric loss data were taken. The amount of dissolved deuterium oxide was determined from the weight-loss of specimens during heating in vacuum, and checked by means of tritium labeling. It is found that dissolved deuterium oxide influences the internal friction and dielectric losses, in the same was as additions of dissimilar alkali ions do (mixed alkali effect) so that one can say that deuterium behaves similarly to alkali ions.A comparison of the present data with the results of a recent study on the influence of protons on the mechanical and electric properties in an identical host glass illustrates clearly that the mixed alkali effect is not governed by mass differences of the cations.     

Anelastic spectroscopy in potassium aluminum metaphosphate glasses

Anelastic spectroscopy (internal friction and the dynamic modulus) was measured by means of a torsion pendulum at 3–12 Hz, in the range of 100–300 K, for a KAP metaphosphate glass. Two thermally activated internal friction peaks appeared at ∼190 and ∼250 K. These peaks were attributed to the behavior of potassium ions (high temperature) and to hydrogen (low temperature). Dynamic modulus showed a gradual decrease with increasing temperature in the range studied for all compositions.     

Internal friction and shear modulus of certain metallic glasses

We have measured the temperature dependence of the internal friction and shear modulus of metallic glass alloys Fe₄₀Ni₄₀P₁₄B₆, Fe₂₉Ni₄₉P₁₄B₆Si₂, Fe₈₀B₂₀ and Fe₇₈Mo₂B₂₀ in the glassy and crystalline phases using a torsional pendulum technique. The internal friction in the glassy phase remains approximately constant from room temperature to a temperature which depends on the annealing treatment, and the rises exponentially with temperature. The internal friction measurements were made at two different frequencies (0.2 Hz and 1.0 Hz) and the activation energies for the relaxation processes estimated by the frequency shift method. The shear modulus increases by about 30% when the amorphous alloys are crystallized. The amorphous alloys Fe₈₀B₂₀ and Fe₇₈Mo₂B₂₀ exhibit Invar type behaviour which disappears upon crystallization.     

Internal friction and dielectric losses of mixed alkali borate glasses

The internal friction and dielectric losses of NaK, LiNa, LiCs, LiK, NaCs, KCs, AgLi, AgNa, AgK and AgCs borate glasses were measured as functions of the temperature at various frequencies. In general, the behavior of mixed alkali borate glasses is very similar to the behavior of the comparable phosphate and silicate glasses. The magnitude of the mixed alkali peak was found to vary systematically with the size of the involved alkali ions. The silver-containing glasses also show the mixed alkali effect. The borate glasses are briefly compared with the silicate and the phosphate glasses and their behavior is found to be in agreement with the recent proposal that the mixed alkali peak is caused by an electro-mechanical cross effect.     

Protonic conduction in alkaline earth metaphosphate glasses containing water

D.c. electrical conductivity data were obtained for M O·P₂O₅ glasses (M = Be, Mg, Ca, Sr, Ba) containing small amounts of water. The results suggest that the mobility of protons in the glasses increases with decreasing OH bonding strength. The relation between the proton concentration and the conductivity or the apparent activation energy was studied for calcium metaphosphate glasses containing various amounts of water. The conductivity was found to be proportional to the square of the proton concentration; the apparent activation energy decreased linearly with increasing logarithm of proton concentration.     

Internal friction in vanadium-phosphate glasses doped with Na2O

The internal friction of _xNa₂O·(0.5−x)V₂O₅·O.5P₂O₅(x = 0.025–0.3) glasses was studied using the low-frequency torsion pendulum technique. The temperature spectrum of internal friction reveals three maxima. Maximum 1, the so-called “electron” maximum, is the same as observed in binary vanadium-phosphate glasses. The origin of maximum 2 can be attributed to ion migration. Maximum 3 appears for glasses containing more than 10 mol.% Na₂O and is probably connected with sodium-proton interactions.     

Internal friction of NaPO3 glasses containing water

The internal friction of sodium metaphosphate glasses containing from 0.016 to 0.330 wt% water has been investigated. Weight loss and infrared absorption measurements were used to determine the water content. Of the two internal friction peaks observed between ?100°C and ～250°C, the second peak occurring above room temperature has a pronounced dependence upon the water content; increasing water content causing the activation energy to decrease as the peak increased in size. A mechanism consisting of the cooperative motion of sodium ions and protons has been proposed for this peak. It is concluded that the second peak in the NaPO₃ glasses and the similar peak in alkali silicate glasses is not associated with the movement of the non-bridging oxygen ions.     

Effect of aluminum ions on intrinsic sub-critical crack growth in metaphosphate glasses

Sub-critical crack growth in various kinds of metaphosphate glasses was investigated by using DCDC (Double Cleavage Drilled Compression) technique. The crack growth measurements were only being made in Region III, or in an inert environment. In order to evaluate intrinsic crack growth behaviors in Region III, crack propagation tests were performed in dehydrated heptane, and the crack velocity, v, was plotted as a function of the stress intensity factor, K_I. Fracture toughness of glass was also estimated from a stress intensity factor at a given crack velocity. For binary metaphosphate glasses (50MO · 50P₂O₅, M = Zn, Mg, Ca, Ba), fracture toughness increases in the order of Mg > Ca > Zn > Ba. However, the slope of K_I–v curve is almost unchanged. In the case of aluminum containing metaphosphate glasses, with increasing aluminum content, fracture toughness increases and the slope of K_I–v curve becomes smaller, regardless of the type of divalent cations in glass. It is concluded that an addition of aluminum ions into metaphosphate glass results in both high toughness and easy fatigue. In addition, the structural role of aluminum ions on the intrinsic sub-critical crack growth is discussed in terms of the models of atomistic bond rupture.     

Internal friction data as explained on the basis of structural-energetic parameters of inorganic glasses

On the basis of a previously reported model the diffusive mechanism of internal friction in microheterogeneous inorganic glasses is discussed. A method of calculating the activation energy, the dimensions of the structure complexes and defects, as well as the masses of relaxing structure elements is proposed. The potentialities of the method for a series of binary and ternary alkali-silicate glasses are shown.     

Structural properties of lithium metaphosphate glasses by ab initio molecular electronic structure calculations

Following a theoretical determination of cluster-models for lithium metaphosphate glass, a theoretical method for the prediction of structural data such as radial and bond distribution functions is presented. These are calculated and compared to experimental data for this particular glass. Useful conclusions are drawn regarding the general use of molecular electronic structure methods for the determination of the structure of glasses.