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The self-diffusion in silicon is investigated in terms of the cBΩ thermodynamic model, which connects point defect parameters with the bulk elastic and expansion properties. The curved Arrhenius plot of the recently reported experimental data on self-diffusion in Si by Kube et al. [Phys. Rev. B 88 (2013) 085206] and by Bracht [Physica B 376–377 (2006) 11] which is associated with two mechanisms (vacancies and self-interstitials) can be explained, if the non-linear anharmonic behavior of the isothermal bulk modulus is considered over the entire temperature range of the available experimental data. The latter suggests the existence of a single diffusion mechanism, in contrast to experimental evidence, which in the frame of the cBΩ model exhibits temperature dependent thermodynamic properties. Indeed, the calculated point defect parameters (activation enthalpy, activation entropy and activation Gibbs free energy) exhibit considerable temperature dependence, with the activation enthalpy varying in a non-linear way from 3.6 eV to 4.9 eV, in agreement with the interpretation of the aforementioned experimental data.

Development of failure in brittle materials is associated with microcracks, which release energy in the form of elastic waves called acoustic emissions. This paper presents results from acoustic emission measurements obtained during three point bending tests on Nestos marble under laboratory conditions. Acoustic emission activity was monitored using piezoelectric acoustic emission sensors, and the potential for accurate prediction of rock damage based on acoustic emission data was investigated. Damage localization was determined based on acoustic emissions generated from the critically stressed region as scattered events at stresses below and close to the strength of the material. Keywords: Acoustic emissions, Three point bending test, Indirect tensile strength, Crack localization, Nestos marble

In the present work, the diffusion coefficients of n- and p-type dopants (P, As, Sb, Al) and self-diffusion in crystalline germanium are calculated from the bulk elastic properties of the host material based on the cBΩ thermodynamic model. The calculated diffusion coefficients as a function of temperature and the activation enthalpies prove to be in full agreement with the reported experimental results. Additional point defect parameters such as activation entropy, activation volume and activation Gibbs free energy are also calculated for each diffusing element. The pressure dependence of self-diffusion coefficients in germanium is also verified at high temperatures (876 K–1086 K), in agreement with reported results ranging from ambient pressure up to 600 MPa and is further calculated at pressures up to 3 GPa, where the phase transition to Ge II occurs.

In the present work, complex electrical impedance measurements in the frequency range of 10 mHz to 1 MHz were carried out in conjunction with acoustic emission monitoring in limestone samples subjected to linear and stepped-like uniaxial loading, up to ultimate failure. Cole–Cole plots of the complex impedance during the stepped loading of limestone have been used to discriminate the contributions of grains interior, grain boundaries and electrode polarization effects to the overall electrical behavior. The latter is well-described with an equivalent-circuit model which comprises components of constant phase elements and resistances in parallel connection. Electrical conductivity increases upon uniaxial loading giving rise to negative values of effective activation volume. This is a strong experimental evidence for the generation of transient electric signals recorded prior to seismic events and may be attributed to charge transfer (proton conduction) due to cracks generation and propagation as a result of the applied stress. The time-series of ac-conductivity at two distinct frequencies (10 kHz, 200 kHz) during linear loading of limestone samples exhibits a strong correlation with the acoustic emission activity obeying the same general self-similar law for critical phenomena that has been reported for the energy release before materials fracture.

In the present work, dielectric and conductivity measurements in the frequency range of 10 mHz–1 MHz were carried out by means of a high-resolution broadband spectrometer on non-swelling bentonite samples, at various low levels of hydration. The evolution of dielectric response was also examined after annealing of the samples up to 260 °C. Conductivity results in conjunction with the electric modulus representation (M∗) is proved to be the most suitable for the analysis of the dielectric data. Dielectric response is dominated by ionic (surface and bulk) conductivity as well as by grain polarization due to migration of ions along the clay layers. Both mechanisms are strongly affected by the concentration of bound water and the thermodielectric effect. Havrilliak–Negami dielectric relaxation functions were used to model the observed relaxations mechanisms in modulus formalism and the fitting parameters were evaluated at various water contents of the measured samples.

In the present work, the wear behavior of nickel superalloy CMSX-186 was studied under various sliding conditions. Nickel superalloys CMSX are alloys that are very strong where creep, fatigue and strain conditions are severe. In the present experiments, the friction coefficient of nickel superalloy CMSX-186 against hardened stainless steel was measured and found to be constant for a constant value of applied load; it was also observed the value of friction coefficient to increase with decreasing applied normal load for a constant value of sliding speed. The main wear mechanism of the material is supposed to be complicated and might be attributed to the simultaneous actions of ductile and brittle friction mechanism.

In the present paper we study the adsorption of Li on C 60 -covered Ni(1 1 0) surfaces by means of Auger electron spectroscopy, low-energy electron diffraction, thermal desorption spectroscopy and work function measurements, in ultrahigh vacuum. During Li deposition on 1 ML C 60 /Ni(1 1 0) surfaces, a considerable amount of charge is transferred to the C 60 overlayer, leading to a partial or complete occupation of the t 1g -derived band of C 60 . The above charge transfer delays the metallization of Li as compared to the clean Ni(1 1 0) surfaces and increases its binding to the Ni(1 1 0) substrate ( E b =1.72 eV/atom). The sticking coefficient of Li remains constant for high Li coverages ( Θ Li ⩾7 MLs), due to its strong interaction with the C 60 overlayer. Charge transfer to the C 60 molecules and reduced metallic character of the Li overlayer is also observed during Li deposition on a (5×3)-C 60 on Ni(1 1 0), while, the presence of the (5×3) islands results in the appearance of Li structures formed in the bare regions of the Ni substrate. In both cases, the presence of C 60 prevents the Li-induced (1×2) reconstruction which is observed for Li deposition on clean Ni(1 1 0) surfaces.

In the present paper we study the adsorption of C 60 on Ni(1 1 0) surfaces at RT and 650 K, as well as the desorption/decomposition process. The investigation took place in UHV by means of Auger electron spectroscopy, low energy electron diffraction, thermal desorption spectroscopy and work function (WF) measurements. The observed overlayer structures during C 60 deposition at 650 K are in complete agreement with reported results. The sticking coefficient is nearly the same for both RT and 650 K. Heating of the 1 ML C 60 -covered Ni(1 1 0) surface, however, at 750 K, causes a partial fragmentation of C 60 to a 2D graphite-like layer, while the remaining C 60 molecules are rearranged in the (5×3) structure, in contrast to reported results. Further heating to 800 K results in the complete fragmentation of C 60 accompanied by carbon desorption, possibly in molecular C n ( n >10) form. Above 800 K, the C of the graphite-like layer is desorbed in both atomic and molecular form. The WF at saturation coverage was found to be 5.61 eV for both deposition at RT and 650 K. This value is substantially greater than the average value of 5 eV, which has been suggested to hold for C 60 overlayer systems, regardless of the metal substrate.

In this paper we study the formation of transition metal selenide thin-films. The investigation took place in ultra high vacuum (UHV) by means of photoemission spectroscopy with synchrotron radiation. The films were produced by simultaneous co-adsorption of TiCl 4 and elemental Se on polycrystalline Ti, Mo and Cu substrates, at 250°C. The above co-adsorption on Ti produces thin-films of TiSe 2 layer compounds, whereas, on the Mo and Cu substrates, Se interacts directly with the substrate producing a MoSe 2 layer compound and Cu 2– x Se thin-films, respectively. Deposited Li is intercalated into both TiSe 2 and MoSe 2 layer compound thin-films while it interacts with the non-layered Cu 2– x Se producing an alkalimetal copper selenide compound (Li x Cu y Se z ). When the above Li x Cu y Se z and Li-intercalated TiSe 2 , MoSe 2 thin films are exposed to TiCl 4 at 140°C, TiCl 4 dissociates, leading to a strong Li + –Cl − interaction and the formation of a LiCl overlayer.

We present the investigation of Li adsorption on Ni(110) surfaces at low temperature (LT) and room temperature (RT) by means of Auger electron spectroscopy, low-energy electron diffraction, thermal desorption spectroscopy and work function measurements, in ultrahigh vacuum. At RT, from the early stages of deposition (Θ≤0.1 ML) Li induces a (1×2) reconstruction of the Ni(110) surface. The (1×2) reconstruction is lifted at 0.5 ML. A further increase of Li coverage leads to a disordered surface, with an intermixing of Li adatoms and the Ni substrate with a tendency toward Li–Ni alloy formation. A gradual heating of the Li-covered Ni(110) surface gives an Li(3×1), an Li(5×1) structure and the (1×2) reconstruction before the complete desorption of Li. Near saturation (Θ≈2 ML), Li forms a nearly metallic overlayer. At LT (150 K), deposition of Li up to 1 ML gives a sequence of c(2×2), (7×2), (3×2), (4×2), (5×4) and finally (1×1) structures, which have been determined using structure factor calculations. These structures are attributed to a continuous stretching of deposited Li atoms along the [110] direction of the Ni(110) surface. The Li–Ni interaction is a thermally activated process and decreases the stability of the Ni surface, leading to its reconstruction at RT. However, at LT the Li–Li interaction dominates and the effect of Li adatoms on the substrate structure is limited. The change of the (1×2) reconstruction to the ideal (1×1) bulk-like surface occurs at the beginning of the transition of ionic to metallic bonding of the Li overlayer.

In this paper, we study the formation of TSe2 (T=Ta, Ti)-layered compound thin films, grown on polycrystalline Ta substrates. The experiments were performed in UHV by means of photoemission spectroscopy with synchrotron radiation measurements. The adsorption of elemental Se on Ta substrate at RT produces a film of Se multilayers. With subsequent heating up to 450°C, the deposited Se interacts with Ta, leading to the formation of a TaSe2 thin film. The simultaneous co-adsorption of Se and TiCl4 on clean polycrystalline Ta at 250°C produces a TiSe2 film of ∼5 molecular layers. The production of TiSe2 film has been confirmed by Na intercalation and following de-intercalation of Na by exposure of the Na/TiSe2 film to TiCl4.

In this paper we study the interaction of Cl 2 and Na on WSe 2 (0001) surfaces in the temperature range 100 to 300 K. The experiments took place in UHV with the use of LEED and photoemission with synchrotron radiation measurements. Adsorption of Na on chlorinated WSe 2 at 100 K results in a direct interaction of Na and Cl, which, with increasing temperature to 300 K, leads to NaCl formation. Adsorption of chlorine on Na-intercalated WSe 2 at 100 K causes the formation of Cl 2 molecular multilayers. The first layer of Cl 2 interacts weakly with Na near the surface. Warming up towards 300 K, part of the Cl 2 overlayers is desorbed, while that remaining on the WSe 2 surface interacts strongly with Na, resulting in the deintercalation of Na to the surface in the tendency to form NaCl.