Electrical conductivity and photoconductivity of As2S3PbS glasses

Measurements of dc electrical conductivity and photoconductivity of various glassy compositions (x = 0.1?0.625) in (As₂S₃)_1?x(PbS)_x have been made. Experimental results of the temperature dependence of dc conductivity from room temperature to 200°C (which includes the glass transition temperature) are reported. All the compositions exhibit intrinsic conduction in the measured temperature range. Thermal activation energy, glass transition temperature and σ₀ for the compositions studied, were determined from the experimental data. The low value of $\text{σ}{}_0\text{(10?10}{}^{\mathrm{?2}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) in these semiconducting glasses is attributed to the greater participation of localized states in the conduction process.In the measurements of photoconductivity, the variation of photocurrent with temperature, photon energy, light intensity and electric field is observed. The recombination model has been involved to explain the results of photoconductivity. Both electrical and photoconductivity data support the presence of higher density of localized states in the x = 0.1 composition than in others.     

Change of short-range order with temperature and composition in liquid GexSe1−x as shown by density measurements

Density measurements were performed on melts of the binary chalcogenide system Ge_xSe_1?x (0 ? x ? 0.5) up to 1000°C. The isotherm of molar volumes V_m at 750°C shows a relative maximum near GeSe₂. Molar volumes of the system behave linearly between GeSe and Se at 1000°C. V_m's of melts between x = 0.30 and x = 0.35 decrease at high temperatures on heating. The anomalous density behaviour of the melts clearly shows a change of short-range order from a less to a more densely packed structure, caused by the development of a pσ-bonding system. Within the composition range $\text{0 ? x ?}\text{1}\text{3}$ the short-range order at lower temperatures is determined mainly by $\text{GeSe}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}$ tetrahedra linked directly corner-to-corner or via Se atoms. At higher temperatures pσ bonds arise more and more, even in melts rich in selenium. Within the composition range $\text{1}\text{3}\text{? x ? 0.5}$ the short-range order is mainly determined by a distorted octahedral configuration, even at lower temperatures. From the short-range orders of melts and from crystalline structures of GeSe₂ and GeSe, the tendency of glass formation from the melt is discussed in detail.     

Electrical transport in n-type semiconducting Ge120BixSe70−xTe10 glasses

Resistivity and thermoelectric power were measured as a function of temperature and composition for Ge₂₀Bi_xSe_70?xTe₁₀ glasses (x = 0–11). The results were compared with the case of of Ge₂₀Bi_xSe_80?x glasses to see on the electrical properties the influence of the substitution of Te for a part of Se. The glasses show n-type conduction for x ? 9, which was not affected by the substitution of Te. The resistivity was about three orders of magnitude lower for the glasses with x < 10, and remained almost the same for x ? 10, compared with the glasses not containing Te. From the composition dependence of the calculated concentration of covalent bonds in the glasses, it was proposed that the appearance of n-type conduction was closely related to the formation of a sufficient number of BiSe bonds and the disappearance of the bonds between two chalcogen atoms such as TeSe or SeSe bonds, and that the remarkably low resistivity in the present glasses with x < 10 was likely to be attributed to the formation of TeSe bonds.     

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.     

Electrical properties of glasses in the GeBiSbSe and GeBiS systems

Measurements of optical absorption, dc conductivity and thermopower were carried out on glasses of the types (GeSe_3.5)₈₈sbPin12?xBi_x. The main results are: 1) observation of n-type conduction in the Ge₂₀Bi_xS_80?x glasses containing high concentrations of Bi; 2) in the mixed doped glasses, transition from p-type for a Sb-doped glass (x = 0) to n-type on addition of Bi at nearly equal concentrations of Sb and Bi. The possible types of bonding of the Bi atoms in the structure and their influence on the electrical behaviour are examined.     

Kinetics of ion exchange in glasses

The kinetics of $\text{K}{}^{\mathrm{+}}\text{?}\text{Na}{}^{\mathrm{+}}$ exchange in two glass systems, 20Na₂O·(60?x)B₂O₃· (20 + x)Si₂ (where x = 0, 15, 30 and 45 mol%) and Na₂O·3SiO₂, were studied as a function of glass composition, salt bath composition, exchange temperature and time The distribution of K in the glass specimens after exchange in molten KNO₃ was determined with an electron probe. Stresses in these speciments were measured photoelastically. The interdiffusion coefficient $\text{D}$ for ion exchange was calculated as a function of local composition in the glass using the Boltzmann-Matano method. The strong variation of $\text{D}$ in any particular glass approximated that predicted by a mixed alkali model (as advanced by Lacharme), where the glass in the ion-exchanged region approximates a composite of stacked layers of mixed alkali glasses with a gradually varying alkali ratio. The small discrepancy between the experiment and the mixed alkali model was partly, but not fully, reconciled by considering the strains in the glasses. The observation which remained unexplained was that the calculated stress profiles did not show perfect agreement, both in magnitude and in shape, with the experimentally measured stress profiles. It appeared that the kinetics of ion exchange in the glasses were also influenced by a network relaxation process which may have occurred well below the glass transition temperature.     

On the structure of amorphous GexTe1−x systems

Calculations have been made for the quadrupole splitting of a $\text{3}\text{2}$ spin state of Te¹²⁵ in an amorphous Ge_xTe_1?x system. The results favour the existence of a threefold coordinated black phosphorus structure with an excess of TeTe chains for x-values between o and 0.5; beyond 0.5, threefold coordinated GeTe and an excess of amorphous Ge coexist.     

Subject index

The structures of phosphorus-selenium glasses P_xPe_1?x with x=0 (pure selenium), 0.05, 0.15, 0.25, 0.40 and 0.50 have been investigated with neutron diffraction, extented, X-ray absorption fine structure measurements, and Raman and infrared spectroscopy. The behavior of the near-neighbor coordination at $\text{r～2.3}\text{A}\text{?}$ as a function of x suggests a picture in which P₄Se_n molecular units are linked together by Se atoms or chains. The diffraction patterns exhibit anomalous peaks at Q ～ 1.2Å which rise dramatically as P is added to the Se glass; these peaks can also be understood on a molecular picture. The Raman spectra at the larger P concentrations are characterized by series of relatively sharp peaks which also suggest molecular units and for x = 0.5 bear a close correspondence to the spectrum of crystalline P₄Se₃.     

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.     

A structural investigation of calcium fluorosilicate glasses

The structure of x CaF₂(1?x)CaOSiO₂ glasses was investigated by X-ray photoelectron, F K_α emission X-ray and infrared absorption spectroscopies and ionic refraction of fluorine. A maximum in F_1s binding energy and a minimum in chemical shift of F K_α X-ray were found in the region of 7–10 mol% CaF₂, indicating that the state of fluorine changes. The ionic refraction of fluorine increased with increasing CaF₂ content up to 7 mol% CaF₂ and was nearly constant for compositions with more than 7 mol% CaF₂. There was practically no change in $\text{Ca}{}_{\mathrm{<mtext>2</mtext><mtext>p</mtext><mtext>(</mtext><mtext>3</mtext><mtext>2</mtext><mtext>)</mtext>}}$ binding energy for compositions with less than 7 mol% CaF₂. These data suggest that the fluorine ion bonds with a silicon predominantly for a CaF₂ content of less than 7 mol% and bonds with a calcium ion for increased CaF₂ content. Further, partial charges of fluorine, calcium and silicon, calculated by the modified Sanderson method could explain the chance of F_1s and $\text{Ca}{}_{\mathrm{<mtext>2</mtext><mtext>p</mtext><mtext>3</mtext><mtext>2</mtext>}}$ binding energies with composition. It is suggested that when the CaF₂ content is more than 7 mol%, the coordination number of fluorine increases and that of calcium decreases with increasing CaF₂ content.     

Relation between electrical and optical gaps of amorphous semiconductors in the SiAsTe system

Electrical and optical properties of semiconducting SiAsTe glasses have been investigated. Compositional dependences of the properties in the Si_xAs_yTe_z system are examined as a function of atomic percentage x (or y, z) of one element with parameters of constant atomic ratio y/z (or x/z, x/y) of the other two elements. A pre-exponential factor σ₀ in the dc conductivity formula is estimated to be $\text{(2.1 ± 0.6) × 10}{}^4\text{(Ω ·}\text{cm}\text{)}{}^{\mathrm{?1}}$, inependently of the compositions. A systematic relationship between the compositional changes in the electrical gap E_g(el) and optical gap E_g(op) has been found. The energy gaps increase linearly with increasing Si content and decreasing Te content, but are almost independent of As content. The relation between E_g(el) and E_g(op) is expressed by E_g(el) = 1.60 E_g(op) ? 0.15 in eV. On the other hand, the optical absorption coefficient α(Ω) near the band edge follows the empirical formula, $\text{α(Ω) = α}{}_0$ exp ($\text{h}\text{?}\text{Ω/E}{}_{\mathrm{<mtext>s</mtext>}}$). The experimentally determined factor E_s increases linearly with E_g(op) and is closely related to the energy difference between the two gaps. A tentative model to explain these experimental results is proposed by taking into account of the effect of the potential fluctuations in such disordered materials.     

Structures of vapour-deposited amorphous films of arsenic chalcogenides

The structures of vapour-deposited amorphous films of composition As_xSe_1?x′, with x between 0 and 1, have been investigated by X-ray diffraction. In all cases the structure of the freshly deposited film differs very considerably from that of the corresponding bulk glass. For the elemental amorphous films the structure is highly disordered and contains voids which for Se cannot be annealed out below the crystallization temperature of 70°C or, for As, below the temperature ($\text{?130°}\text{C}$) where the As film re-evaporated. Annealing of the arsenic selenide films at temperatures below T_g causes the structures to relax towards those of the bulk, with a distribution of activation energies around 25 kJ mol^?1. The composition of the vapour has been examined by mass spectroscopy and it is concluded that even if some molecular identity is retained on condensation there must be considerable cross-linking to give the observed structural behaviour.     

Ion exchange between glass melts of the system Na2ORb2OSiO2

Ion exchange between glass melts of the quasi-binary system Na₂O · 3SiO₂Rb₂O₂ was investigated at 700—1300°C by means of a special capillary method. Concentration profiles were obtained by electron microprobe analysis and were evaluated for a concentration-dependent quasi-binary interdiffusion coefficient $\text{tilde}\text{D}$ using a modified Boltzmann-Matano method. At 700–1000°C interdiffusion could be obtained in pure form with $\text{tilde}\text{D}$ values ranging from about 10^?7 ?5 × 10^?6 cm² s^?1. Above 1000°C convection processes superimposed interdiffusion, making a further evaluation impossible. The data are compared with those from a 0g rocket experiment and are discussed with respect to a mixed-alkali effect and in terms of the Nernst-Planck diffusion model.     

Thermal expansion and density of glassy PdNiP and PtNiP alloys

Thermal expansion and density of (Pd_1?xNi_x)_0.80P_0.20 and (Pt_1?yNi_y)_0.75P_0.25 alloys in their various states have been measured from room temperature to the glass transition temperature T_g. The thermal expansion of the glassy alloys at room temperature varies linearly with x and y and is 10 to 20% higher than that of corresponding pure metals. The thermal expansion of the undercooled alloy liquids near T_g as well as the molar volume $\text{v}\text{?}$ deduced from the density of glasses in contrast exhibits a negative deviation with composition x and y.This behavior is in line with the previously reported negative deviation of the glass transition temperature of these glassy alloys with metal content and may be explained in terms of excess volume associated with a mixture of hard spheres.     

ESR and optical absorption of cupric ion in borate glasses

ESR and optical absorption of Cu²⁺ were measured in xNa₂O(100?x)B₂O₃ (1 ≤ x ≤ 75), x ZnO(100?x)B₂O₃ (46 ≤ x ≤ 64) and x Pb(100?x)b₂O₃ (20 ≤ x ≤ 75) glasses, where x is expressed in mol.%. Spin hamiltonian parameters and ligand field absorption energy changed abruptly in the regions of 15 ≤ x ≤ 23 and 37 ≤ x ≤ 55 in the soda system, while both parameters were hardly dependent upon the glass composition in zinc and lead systems. The magnitude of micro-environmental fluctuation of Cu²⁺-complexes in the glasses was estimated qualitatively and correlated with the distribution of the strength of π-bonding between cupric ion and oxygen in the glass. Typical network modifiers and intermediates behaved differently, especially in the composition region of invert glass; the large deformation of the coordination sphere of Cu²⁺ in lead glasses due to the stronger PbO bond resulted in the large distribution of $\text{g}{}_{\mathrm{}}$. The situation was reverse in the case of soda glasses.     

Vapor phase transport and stoichiometry control of cadmium sulfo-selenide

Cadmium sulfo-selenide Cd_1+y(S_xSe_1?x) single crystals were grown by the sublimation method under controlled partial pressures of sulfur and selenium. The partial pressure control was achieved by amounts of sulfur and selenium introduced in a closed growth tube. To control the deviation from stoichiometry y for the specified compositions x, the sum of chalcogen partial pressures Pps(=p_S2+P_Se2) was regulated, holding the partial pressure ratio () constant. The comp osition x of single crystals, grown with appreciable growth rate, was found to be the same one as the source specimen but the electrical conductivity changed extremely from 1 to 10^-12 (ω cm)^-1 with increasing Pps. Hall effect and thermally stimulated current (TSC) were also measured on the high and low conductivity specimens respectively and found to depend upon the controlled Pps. From these experimental results, it was confirmed that the deviation from stoichiometry y was effectively controlled. The transport rate was also precisely measured as a function of controlled Pps.     

The investigation of the magnetic interaction between Cu2+ and V4+ ions in x(CuO·2V2O5)(1 − x)[2B2O3·K2O] glasses

EPR and magnetic susceptibility measurements have been performed on (CuO·2V₂O₅)(1?x)[2B₂O₃·K_2O] glasses with 0 ? x ? 40 mol. %.For x < 10 mol.%, both Cu²⁺ and V⁴⁺ ions are present mostly as the isolated species. The values of MO coefficients indicate a high covalent degree of the transition metal (TM)-oxygen bonds. Also, the EPR parameters suggest the presence of strong (TM)-oxygen bonds along the 0_z axis, which lead to an octahedral (Oh) symmetry component at TM ions sites.In the case of 10 ? x ? 40 mol.%, the dipole-dipole and superexchange interactions occur between transition metal ions, which determine a broad resonance line at $\text{g ? 2}$. The strong interactions between Cu²⁺ and V⁴⁺ ions give rise to the exchange coupled Cu²⁺ V⁴⁺ pairs in the studied glasses with x > 10 mol.% (y > 3.9 mol.%).     

Network structure of sodium and potassium borosilicate glass systems

Molar volumes and optical absorption spectra of Ni²⁺ ions were measured for sodium and potassium borosilicate glasses of the compositions xR₂O·B₂O₃·rSiO₂ (0.01 < x < 2.0; r = 1 and 2), where parameters x and r represent respectively the molar ratios R₂O/B₂O₃andSiO₂/B₂O₃. The presence of structural groups was discussed from the results. It was confirmed that addition of an alkali oxide changed BO₃ units to RBO₄ units in the range x < 0.55 for r=1 and x < 0.6 for r=2, while it created ROSiO₃ units in the range $\text{0.55 < x < 0.8}\text{for}\text{r=1}\text{and}\text{0.6}\text{x}\text{?}\text{< 0.9}\text{for}\text{r=2}$. In the range x > 0.8 for r=1 and x > 9 for r=2, ROSiO₃ and ROBO₂ units were created by the alkali addition. Here ROBO₂ units were also formed as a result of self-decomposition of RBO₄ units. The volume of void associated with a BO₄ unit was calculated and compared with the size of sodium and potassium ions. It was shown that sodium ions were small enough to be accommodated in the void whereas potassium ions were too large. This could explain the composition dependence of the molar volume of the sodium and potassium borosilicate glasses in the composition range x < 0.55 for r = 1 and x < 0.6 for r =2.