LPE growth kinetics of CaGe-Substituted EuTm2Fe5O12 garnet films

The diffusion-reaction growth melts fluxed with PbO-B₂O₃-Fe₂O₃, has been extended to include a thermally-activated diffusion term. The fluxed melt had a lower PbO : B₂O₃ ratio (11 : 1) than that generally used (≈16 : 1) for garnet LPE films. Measured growth rates for LPE films, produced from melts with four different concentrations of CaGe-Substituted EuTm₂Fe₅O₂ garnet, fit the model with: diffusivity, $\text{D (cm}{}^2\text{/s) = 0.06 exp(}\text{-1.0 eV}\text{kT}\text{)}$; reactivity, $\text{K (cm/s) = 8000 exp(}\text{-1.61 eV}\text{kT}\text{)}$; viscosity, $\text{v (}\text{cm}{}^2\text{s}\text{) = 0.01}$; and concentration, $\text{c}{}_{\mathrm{e}}\text{(}\text{g}\text{cm}{}^3\text{) = 4220 exp ?}\text{1.0678 eV}\text{kT}$ for rotation rates ω (rpm) = 36 to 196 in the growth temperature range 890 to 965°C. It is shown that the garnet melt concentration terms are the most critical ones in determining the growth rate, hence the activation energy (heat of solution) for the equilibruim concentration is reported to five significant figures. Evaluating the D and the K effects by both a numerical (results given above) and an analytic method demonstrates that these parameters are least critical in determining the growth rate in this case.     

Energy transfer in Eu3+-Yb3+ and Tb3+-Yb3+ system in glasses

The behavior of the phonon-assisted energy transfer between trivalent rare-earth ions in glasses was investigated. The ions Eu³⁺ and Tb³⁺ as energy donors and Yb³⁺ as acceptor were selected. The energy gap between the levels of the donor and acceptor was estimated on the basis of the energy diagram of each ion determined from absorption and emission spectra. The probability for the transfers of (Eu, ⁵D₀-⁷F₆): (Yb, ${}^2\text{F}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{-}{}^2\text{F}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$) and (Tb, ⁵D₄-⁷F₀): (Yb, ${}^2\text{F}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{-}{}^2\text{F}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$) in silicate, borosilicate, phosphate and germanate glasses was measured in the temperature range of liquid-nitrogen temperature - 650K. The probability of transfer was the smallest in phosphate glass and B₂O₃ had the effect of increasing it. In germanate glass the dependence of the probability of the energy gap was relatively weak. These results were correlated to the difference in the phonon energy and the strength of the electron-lattice coupling in each glass.     

Silver sulfide based glasses (I). Glass forming regions,structure and ionic conduction of glasses in GeS2Ag2S and GeS2Ag2SAgI systems

Ag₂S forms with GeS₂ stable glasses over a wide range of compositions (0–55% Ag₂S mol%). In the same system, more complex glasses obtained by dissolving silver iodide have been synthesized with up to 50 mol% AgI.Raman spectra are presented and a vibrational assignment in terms of bridging and non-bridging sulfur has been made. The electrical conductivity of these glasses has been measured over a temperature range (?50°C? + 50°C) and for various compositions by the complex impedance diagram method. At 25°C, the conductivity reached a maximum value of 6 × 10^?3 Ω^?1 cm^?1. Whatever the glass used, the same limit value of conductivity $\text{(σ ? 10 su?2 Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) and activation energy ($\text{E}{}_{\mathrm{\sigma }}\text{? 0.25}\text{eV}$) are obtained for the highest content of silver iodide. A conduction mechanism is proposed.     

Pressure and heating rate dependence of the crystallization temperature for amorphous (Fe65Ni35)75P16B6Al3 and Ti50Be40Zr10

The crystallization temperature, T_x, was determined at constant heating rate, $\text{R =}\text{T}\text{?}\text{? 7}\text{K min}{}^{\mathrm{?1}}$, by monitoring the electrical resistance. Such experiments were carried out under pressures up to 2.5 GPa, and the resulting dT_x/dP was 15.9 K GPa^?1 for (Fe₆₅Ni₃₅)₇₅P₁₆B₆Al₃ and 8.7 K GPa^?1, 8.1 K GPa^?1 for the two crystallization processes in Ti₅₀Be₄₀Zr₁₀. The activation energies of crystallization under atmospheric pressure were obtained from measurements of T_x at rates from 0.05 K min^?1 ?55 K min^?1, analysed by plotting ln(T_x²R^?1) versus T_x^?1.     

The preparation and electrical switching properties of nickel sulphides in As2S3 glass

A preliminary investigation into the formation of ‘glasses’ from mixtures of arsenic and nickel sulphides is reported. Memory- and threshold-switching devices have been produced from glasses containing particles of nickel sulphide. Threshold switches show a high resistance in the off-state ($\text{> 10}{}^6\text{μ}$), and a linear on-state.     

Retarded elasticity in B2O3GeO2 glasses

The retarded elasticity was investigated for B₂O₃GeO₂ glasses having network structure in the glass transition range by using a compressive method. The compliance (J_∞) determined at the final stage of each measurement displayed a maximum for roughly constant viscosity (η ? 10¹⁴ P) in all the B₂O₃GeO₂ glasses and was simulated by the same equation applied for AsS glasses reported in a previous paper [1].

$\text{J}{}_{\mathrm{\infty }}\text{=(1?k}{}_2\text{keta;}{}_{\mathrm{G}}\text{keta;}\text{)[?}{}_1\text{(}\text{k}{}_1\text{keta;}\text{)+?}{}_2\text{(}\text{nk}{}_1\text{keta;}\text{)]}$

, where $\text{K}{}_1\text{, k}{}_2\text{, ?}{}_1\text{, ?}{}_2\text{and}\text{n}$ are parameters and η_G is the viscosity related to the retarded elasticity. The terms (k₁/η) and (nk₁/η) are assumed to be equal to one for all their values exceeding one. For B₂O₃GeO₂ glasses, the deformation due to the retarded elasticity could be alloted to two structural elements: the first element related to the term $\text{?}{}_1\text{(k}{}_1\text{/η)}$ and the second element related to the term $\text{?}{}_2\text{(nk}{}_1\text{/η)}$. The values of $\text{?}{}_1$ showed almost no variance with the glass composition, but $\text{?}{}_2$ had a minimum at the composition of 50 mol% GeO₂. These data suggest that the contribution of the second element is the smallest at B₂O₃/GeO₂ = 1. The values of k₂ were close to that of As₂S₃ glass having the network structure. k₁ and n (or nk₁) were almost constant regardless of the composition, respectively. These data suggest that the inhibition due to the viscosity starts at an approximately constant viscosity in B₂O₃GeO₂ glasses.     

The structure analysis liquid Sb2Se3 by neutron diffraction

The radial distribution analysis of liquid Sb₂Se₃ at 670, 720 and 770°C is carried out by the neutron diffraction method. A small but apparent maximum is found at $\text{K = 1.2}\text{A}\text{?}{}^{\mathrm{?1}}$ in the structure factor. The interatomic distance and the coordination number are 2.74 Å and 2.84 respectively, at 670°C. These results suggest that intramolecular bonds in the crystalline Sb₂Se₃ remain unbroken in the liquid state. The general feature of the structure factor and the distribution function for liquid Sb₂Se₃ is similar to that for the amorphous state. However, it is clear that the liquid phase tends to have a similar atomic arrangement to that of liquid tellurium.     

Solarization mechanism of glass containing Ce3+ and As5+

The solarization mechanism in a glass containing both Ce³⁺ and As⁵⁺, 16Na₂O·11CaO·73SiO₂:0.15AsO_x·0.015CeO_x (in mol.%), is newly proposed by elucidating the valence and coordination structure of arsenic after the photochemical reaction, the mechanism being traditionally expressed as

$\text{2}\text{Ce}{}^{\mathrm{3+}}\text{+}\text{As}{}^{\mathrm{5+}}\text{→}\text{hv}\text{2}\text{Ce}{}^{\mathrm{4+}}\text{+}\text{As}{}^{\mathrm{3+}}$

ESR hyperfine quartets due to an As⁴⁺ ranging from 0.1 to 0.5 T built up on UV-irradiation and their line shape varied with the duration of the irradiation. The line shape analysis of the ESR spectra employing a computer simulation technique has led to the following conclusions; (1) As⁵⁺ is reduced to As⁴⁺ in the solarization process. (2) The geometry around the As⁴⁺ in the solarized glass is tetrahedral during the early stage and trigonal-pyramidal during the latter stage of the reaction.     

Photoconductivity and photoluminescence of a-Si:H at low temperature

We have studied the temperature dependence of the photoluminescence steady state and transient photoconductivity of a-Si:H down to 4 K. Below 50 K we observe photoconductivity with $\text{ημτ ? 10}{}^{\mathrm{?11}}\text{cm}{}^2\text{/}\text{V}$, which is independent of temperature and varies only little with the defect density in the films. We propose that this conduction arises predominantly from the drift of the photoexcited electrons and holes during thermalization in the extended states prior to the localization in states below the mobility edge. An important implication of the present data is that, even at helium temperatures, a considerable part of the carriers recombines in a non-geminate process.     

Temperature dependence of hopping transport in polymeric semiconductors

We report the results of measurement and analysis of the electrical conductivity of two synthetic highly purified copolymers of the polyacene quinone radical (PAQR) type. The dc conductivity was examined as a function of temperature and pressure. The conductivity-pressure relation is observed to go as log σ versus $\text{P}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. The conductivities under moderate pressure (400–5000 atm) show linear relationships on log σ versus $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ plots in the temperature range 70 K < T < 300 K. The possible interpretations as variable range hopping or as nearest neighbour hopping with distributions of activation energies are discussed.     

On mechanisms of structural relaxation in a Pd48Ni32P20 glass

Structural relaxation processes are investigated calorimetrically for a pre-conditioned Pd₄₈Ni₃₂P₂₀ glass over a wide temperature range from well below to just above the glass transition. The low temperature anneals further stabilize the glassy structure. Upon heating, the annealed sample shows an excess endothermic specific heat ΔC_p above the annealing temperature and completely recovers the initial enthalpy before any manifestation of glass transition, T_g. Significantly the ΔC_p peak evolves in a continuous manner with annealing time. A physically reasonable activation energy spectrum $\text{N}{}_0{}^1\text{(Q)}$ is obtained with the proper choice of coupling constants which are dependent on annealing temperature. Results suggest the existence of localized relaxation modes which do not contribute to macroscopic flow. A concept of distribution in glass transition temperatures H(T_g,m) is conceived to account for the reversible relaxation with temperature. A model glass transition based on percolation theory is proposed and is found to reproduce the calorimetric relaxation phenomena well.     

Mass spectrometric study on chemical transport of VO2

The analysis of gas in the chemical transport reaction of VO₂ using TeCl₄ as a transport agent was carried out with a quadrupole mass spectrometer. In the transport reaction from 600 to 500°C, it was found that the oxygen and vanadium of VO₂ were transported in the form of VOCl₃ and TeOCl₂ gases; the transport reaction was $\text{VO}{}_2\text{+}\text{3}\text{2}\text{TeCl}{}_4\text{= VOCl}{}_3\text{+ TeOCl}{}_2\text{+}\text{1}\text{2}\text{TeCl}{}_2$. The transport reaction from 900°C to 800°C was assumed to be $\text{VO}{}_2\text{+}\text{3}\text{2}\text{TeCl}{}_2\text{= VOCl}{}_3\text{+}\text{1}\text{2}\text{O}{}_2\text{+}\text{3}\text{4}\text{TeCl}{}_2$. In the transport at high temperature, the oxygen partial pressure estimated from the mass spectrum was considerably higher than that in equilibrium with VO₂ phase. In this paper a study of the chemical transport of the system VO₂-TeCl₄ is presented.     

Radiative and non-radiative transition probabilities and quantum yields for excited states of Er3+ in germanate and tellurite glasses

Absorption and fluorescence spectra of Er³⁺ in germanate and tellurite glasses were obtained. Spontaneous transition probabilities of the ${}^4\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and ${}^4\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ to all terminal levels of Er³⁺ were calculated using the Judd-Ofelt theory and intensity parameters obtained from measured intergrated absorption coefficients. Quantum efficiencies of the ${}^4\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and ${}^4\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ fluorescences were measured by the comparative method and by the use of measured decay times. Multiphonon relaxation rates for ${}^4\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^4\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ and ${}^4\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ were calculated using the experimental data. The average rate for ${}^4\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^4\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ in germanate is 1.16 × 10⁵ sec^?1 and in tellurite is 1.60 × 10⁴ sec^?1, and the rate for ${}^4\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{is}\text{2.85 × 10}{}^5\text{sec}{}^{\mathrm{?1}}$ in germanate and 2.33 × 10⁵ sec^?1 in tellurite. The higher rates in germanate glasses are explained by the stronger interaction of the glass phonons with the electronic states of Er³⁺ in germanate than in tellurite glasses. This also explains the higher quantum yield of the visible fluorescence of Er³⁺ in tellurite glasses compared to other glasses.     

Prediction of glass-forming ability for metallic systems

The relative glass-forming ability (GFA) of metallic alloys is considered in terms of a parameter $\text{ΔT}{}^1\text{= (T}{}_{\mathrm{<mtext>liq</mtext>}}{}^{\mathrm{<mtext>mix</mtext>}}\text{? T}{}_{\mathrm{<mtext>liq</mtext>}}\text{)/T}{}_{\mathrm{<mtext>liq</mtext>}}{}^{\mathrm{mix}}$, which represents the departure of the alloy liquids temperature, T_liq, from that of the simple rule of mixtures liquids temperature, T_liq^mix. For values of $\text{ΔT}{}^1\text{> 0.20}$ a metallic system is likely to form a glass by melt-quenching in useful thicknesses (i.e. > 20 μm) at a cooling rate of 10⁵?10⁷ K s^?1. Hence, a rapid assessment of the GFA of novel compositions may in general be obtained simply from a knowledge of the melting points of the pure components and the liquidust emperatures of the alloys.     

Effect of thermal history on conductivity and electrical relaxation in alkali silicate glasses

Electrical conductivity σ₀ and electric field relaxation measurements have been carried out as a function of thermal history for two alkali silicate glasses, Na₂O3SiO₂ and K₂O3SiO₂. Specimens of each glass with three different thermal histories, two of the anneal-and-quench type and one of the rate-cool type, were studied. The average structural or fictive temperature T_f of each of the specimens was characterized by measuring their indices of refraction. Effects of thermal history on σ₀ and its activation enthalpy $\text{H}{}_{\mathrm{\sigma }}{}^1$ were in accord with results of previous investigators. That is, for a given type of thermal history σ₀ was lower and $\text{H}{}_{\mathrm{\sigma }}{}^1$ higher the lower T_f. In addition it was found that for two specimens with the same T_f or index of refraction but different thermal histories the rate-cooled specimen exhibited a lower conductivity than the annealed-and-quenched specimen, in accord with the results of Ritland. The distribution of relaxation times τ_σ for decay of the electric field due to ionic migration was found to be due primarily to a distribution in the pre-exponential term ln $\text{τ}{}_{\mathrm{\sigma }}{}^1$ in the equation $\text{ln}\text{τ}{}_{\mathrm{\sigma }}\text{=}\text{ln}\text{τ}{}_{\mathrm{\sigma }}{}^1\text{+ H}{}^1\text{/RT}$; the distribution in $\text{H}{}^1$ was extremely narrow. Differences in thermal history caused small differences in the distribution of τ_σ, but no difference in the average activation enthalpy $\text{〈H}{}^1\text{〉}$ for τ_σ. From this result it appeared that the dependence of the conductivity activation enthalpy $\text{H}{}_{\mathrm{\sigma }}{}^1$ on thermal history was due to the effect of thermal history on the temperature dependence of the distribution in τ_σ.     

XPS study of glassy Pd80Ge20

An X-ray photoemission and Auger electron spectroscopy study of the electronic structure of Pd₈₀Ge₂₀ alloy in its glassy and crystalline states is reported. The glassy state shows some modifications in the valence band structure, symmetry of the Pd $\text{3}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{?3}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ spin-orbit doublet and a shift in M₄₅-V-V Auger transition of Pd. Analysis of the chemical shifts in the core-level binding energies of the constituents indicates negligible charge transfer from the metalloid atom (Ge) to d-band of the Pd.     

Crystal growth of SnO2 by chemical transport method

Single crystals of SnO₂ were grown by the chemical transport method from the powder prepared by heating hydrous stannic oxide. The transport reactions were carried out when iodine and sulfur were simultaneously used as transporting agent, and fine crystals of a few millimeters in dimensions were grown after a ten-day transport; the transport proceeded from 1100°C (charge) to 900°C part in a silica ampoule. The crystals were identified as SnO₂ (cassiterite) by the Weissenberg method. Thermodynamic calculations led to the equilibrium $\text{SnO}{}_2\text{(s) + I}{}_2\text{(g)}\text{+}\text{1}\text{2}\text{S}{}_2\text{(g)}\text{?}\text{SnI}{}_2\text{(g) + SO}{}_2\text{(g)}$ for this transport reaction.     

Electrical properties of glassy AsxGe10Te90−x alloys

This paper analyses the electrical properties of glassy alloys of As_xGe₁₀Te_90?x, while reporting the conductivity and dielectric constant of As₅Ge₁₀Te₈₅ and As₁₅Ge₁₀Te₇₅ compositions in the temperature range 77–383 K and the frequency range from dc to 5 MHz. The dc conductivity has been shown to be of the form

The ratio σ₀₁/σ₀₂ is of the order of 10⁶. ΔE₁, the higher temperature activation energy, is dependent on the composition, while ΔE₂, the lower temperature activation energy, is less dependent on the composition. The dielectric constant has been found to be independent of temperature and frequency up to about 253 K. However, at higher temperatures, it becomes activated and proportional to log ω.Some common features of As_xGe₁₀Te_90?x are a kink in dc conductivity, a ω^0.8 relationship for ac conductivity, no evidence of variable-range hopping at low temperatures, field-dependent conductivity and memory switching. The data can be interpreted in terms of the dangling-bond theory of Mott and his collaborators. A high density of states of the order of 10²⁰eV^?1 cm^?3 near the Fermi level may be expected.     

Pressure dependence of the elastic moduli of glasses in the K2OSiO2 system

The elastic moduli and their variation with pressure have been determined for three glass compositions in the K₂OSiO₂ glass system. The results may be summarized:

     

20.

A new method of stirring for LPE growth     

J.C. Brice  J.M. Robertson  H. van der Heide 《Journal of Crystal Growth》1975

This paper describes a method of stirring a liquid during crystal growth in which each point on the growth face moves round a circle of radius b. If the face has a radius a and completes n revolutions per second, then the stirring is roughly equivalent to rotating the disc about a single axis at a rate $\text{2πc}{}^2\text{b}{}^2\text{n}\text{a}{}^2$ where c is a constant (c ∽ 2) but the system behaves as if only the liquid up to a distance $\text{(}\text{2v}\text{n}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ from the face is stirred. Uniform stirring occurs over the whole face except for an annulus of width 2b at the periphery. The necessary design criteria are discussed and a simple dynamically balanced apparatus and the results obtained with it whilst growing iron garnet films are described.     

Property/Composition	0.15K2O–0.85SiO2	0.25K2O–0.75SiO2	0.33K2O–0.67SiO2
Shear modulus $\text{G(}\text{kb}\text{)}$	266	241	231
Bulk modulus $\text{K}{}_{\mathrm{<mtext>s</mtext>}}\text{(}\text{kb}\text{)}$	310	283	273
Young's modulus $\text{E(}\text{kb}\text{)}$	620	564	540
($\text{?K}{}_{\mathrm{<mtext>s</mtext>}}\text{/?P)}{}_{\mathrm{<mtext>500\; </mtext><mtext>K</mtext>}}$	?5.1	?4.4	?3.9
($\text{?G/?P)}{}_{\mathrm{<mtext>500\; </mtext><mtext>K</mtext>}}$	?2.8	?2.6	?2.5
Poisson's ratio σ	0.167	0.168	0.170
($\text{?σ/?P) (}\text{x}\text{10}{}^{\mathrm{?3}}$)
(kb?1)	?1.5	?1.2	?0.95

A new method of stirring for LPE growth

This paper describes a method of stirring a liquid during crystal growth in which each point on the growth face moves round a circle of radius b. If the face has a radius a and completes n revolutions per second, then the stirring is roughly equivalent to rotating the disc about a single axis at a rate $\text{2πc}{}^2\text{b}{}^2\text{n}\text{a}{}^2$ where c is a constant (c ∽ 2) but the system behaves as if only the liquid up to a distance $\text{(}\text{2v}\text{n}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ from the face is stirred. Uniform stirring occurs over the whole face except for an annulus of width 2b at the periphery. The necessary design criteria are discussed and a simple dynamically balanced apparatus and the results obtained with it whilst growing iron garnet films are described.