Isothermal kinetics and relaxation recovery of high-frequency shear modulus in the course of structural relaxation of Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> bulk glass

Isothermal kinetics of relaxation of the high-frequency (1.4 MHz) shear modulus during structural relaxation of Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk metallic glass below the glass transition temperature is studied by an in situ method of contactless electromagnetic acoustic transformation. The kinetic law of relaxation is established. It is shown that quenching of aged samples from the supercooled liquid state leads to a decrease in the absolute value of shear modulus to below the initial value; the degree of subsequent isothermal relaxation of the modulus may be several times higher than the initial value. Possible reasons for relaxation and recovery of the shear modulus are considered.     

Kinetics of structural relaxation of bulk and ribbon Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> glasses determined from electrical resistance measurements

The electrical resistances of ribbon and bulk Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glasses, whose quenching rates differ by four orders of magnitude, were precisely measured during cyclic heating. Three stages of electrical resistance relaxation are detected as the maximum heating temperature increases. The first and third stages decrease the electrical resistance, and the second stage increases it. The first stage is shown to be caused by the relaxation of deformation-induced internal stresses and not to be related to the excess free volume concentration, which differs by a factor of about 2 in the ribbon and bulk samples. The second stage reflects structural relaxation in the glass and is only partly related to its free volume. The third relaxation stage is assumed to be caused by fine precrystallization phenomena like phase separation. The effect of deformation by rolling or quenching from the temperature range of a supercooled melt on the resistance relaxation kinetics was also studied.     

Compression behavior of Zr<Subscript>41</Subscript>Ti<Subscript>14</Subscript>Cu<Subscript>12.5</Subscript>Ni<Subscript>10</Subscript>Be<Subscript>22.5</Subscript> bulk metallic glass up to 24 GPa

The compression of a Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) is investigated at room temperature up to 24 GPa using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The pressure-induced structural relaxation is exhibited. It is found that below about 8 GPa, the existence of excess free volume contributes to the rapid structural relaxation, which gives rise to the rapid volumetric change, and the structural relaxation results in the structural stiffness under higher pressure.     

Nonradiative relaxation of photoexcited O<Stack><Subscript>1</Subscript><Superscript>0</Superscript></Stack> centers in glassy SiO<Subscript>2</Subscript>

The processes involved in the excited-state relaxation of hole O ₁ ⁰ centers at nonbridging oxygen atoms in glassy SiO₂ were studied using luminescence, optical absorption, and photoelectron emission spectroscopy. An additional nonradiative relaxation channel, in addition to the intracenter quenching of the 1.9-eV luminescence band, was established to become operative at temperatures above 370 K. This effect manifests itself in experiments as a negative deviation of the temperature-dependent luminescence intensity from the well-known Mott law and is identified as thermally activated external quenching with an energy barrier of 0.46 eV. Nonradiative transitions initiate, within the external quenching temperature interval, the migration of excitation energy, followed by the creation of free electrons. In the final stages, this relaxation process becomes manifest in the form of spectral sensitization of electron photoemission, which is excited in the hole O ₁ ⁰ -center absorption band.     

Structural relaxation of Zr<Subscript>41</Subscript>Ti<Subscript>14</Subscript>Cu<Subscript>12.5</Subscript>Ni<Subscript>10</Subscript>Be<Subscript>22.5</Subscript> bulk metallic glass under high pressure

Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) is annealed at 573 K under 3 GPa and its structural relaxation is investigated by X-ray diffraction, ultrasonic study, compression as well as sliding wear measurements. It is found that after the ZrTiCuNiBe BMG sample was annealed under high pressure, the mechanical properties were improved. Moreover, theBMG with relaxed structure exhibits markedly different acoustic properties. These results are attributed to the fact that relaxation under high-pressure results in a microstructural transformation in the BMG.     

Effect of nanocrystallization on the mechanical and magnetic properties of finemet-type alloy (Fe<Subscript>78.5</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript>)

The kinetics of primary crystallization and the effect of structural parameters of the precipitating nanocrystalline α-phase Fe-Si on changes in microhardness, coercive force, and saturation magnetization in an amorphous Finemet-type 5BDSR alloy (Fe_78.5Si_13.5B₉Nb₃Cu₁) obtained by melt quenching are studied. It is found that both an increase in bulk density and an increase in the average nanoparticle size contribute to the hardening of the amorphous/nanocrystalline alloy.     

Shear viscosity of the Pd<Subscript>40</Subscript>Cu<Subscript>40</Subscript>P<Subscript>20</Subscript> metallic glass under conditions of isochronous heating below the glass transition temperature

The shear viscosity is measured under conditions of isochronous (linear) heating below the glass transition temperature of the Pd₄₀Cu₄₀P₂₀ metallic glass, which is characterized by the polymorphic crystallization into the Pd₂Cu₂P tetragonal phase with a lower density than the initial glass. It is shown that the rate dependence of the shear viscosity can be interpreted as a result of the irreversible structural relaxation by analogy with the case of the previously studied metallic glasses despite the unusual ratio of the densities of the material in noncrystalline and crystalline states.     

Magnetically controlled thermoelastic martensite transformations and properties of a fine-grained Ni<Subscript>54</Subscript>Mn<Subscript>21</Subscript>Ga<Subscript>25</Subscript> alloy

Comparative studies of physical characteristics (the electrical resistivity, the magnetic susceptibility, the magnetization, the bending deformation, and the degree of shape recovery during subsequent heating) of the Ni₅₄Mn₂₁Ga₂₅ ferromagnetic alloy as-cast and rapidly quenched from melt have been performed in the temperature range 2–400 K. The results are compared to the results of studying the structural–phase transformations by transmission and scanning electron microscopy and X-ray diffraction. It is found that the rapid quenching influences the microstructure, the magnetic state, the critical temperatures, and the specific features of thermoelastic martensite transformations in the alloy. It is found that the resource of the alloy plasticity and thermomechanical bending cyclic stability demonstrates a record-breaking increase in the intercritical temperature range and during subsequent heating.     

Dependence of the optical properties of Fe<Subscript>78</Subscript>Si<Subscript>10</Subscript>B<Subscript>12</Subscript> amorphous alloy on its structural state

The optical properties of Fe₇₈Si₁₀B₁₂ ferromagnetic alloy in amorphous, crystalline, and intermediate structural states have been investigated by ellipsometry in the spectral range of 0.22–18 μm. It is established that alloy crystallization leads to a significant change in the optical constants and the frequency dependences of the dielectric functions calculated based on these optical constants. The structural reconstruction under heat treatment leads to an increase in the intensity and shift of interband absorption bands. The plasma and relaxation frequencies of conduction electrons are determined; their numerical values also depend on the degree of atomic ordering.     

<Emphasis Type="Italic">In situ</Emphasis> X-ray diffraction study of structural evaluation in Fe<Subscript>73</Subscript>Cu<Subscript>1.5</Subscript>Nd<Subscript>3</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript> amorphous alloy at high temperature

The thermodynamics structural relaxation of Fe₇₃Cu_1.5Nd₃Si_13.5B₉ amorphous alloy from room temperature to 400°C has been investigated by measuring the structure factor with in situ X-ray diffraction. The structural information of the atomic configuration such as radial distribution function (RDF) and neighbor atomic distance was gained by Fourier transformation. The research result shows that the amorphous structure remains stable in the temperature range of 30 to 400°C but exhibits distinct changes in local atomic configuration with the increase of temperature. The quantitative determination of the neighbor atomic distance suggests that the degree of short-range order changes by the temperature altering the second nearest neighbor local atomic configuration of the amorphous when structural relaxation occurs. Supported by the Natural Science Foundation of Hebei Province of China (Grant No. A2007000296), the National Natural Science Foundation of China (Grant No. 50731005), SKPBRC (Grant Nos. 2007CB616915 and 2006CB605201), and PCSIRT (Grant No. IRT0650)     

Molecular-dynamics study of the Ni<Subscript>60</Subscript>Ag<Subscript>40</Subscript> binary alloy glass transition

Features in the evolution of the atomic structure of the Ni₆₀Ag₄₀ alloy upon quenching from a liquid disordered state were revealed within the molecular-dynamics method using many-particle potentials of interatomic interaction, calculated within the embedded atom method. It was shown that the structural stabilization of the amorphous Ni₆₀Ag₄₀ phase during the glass transition occurs due to the formation of a percolation cluster of interpenetrating and contacting icosahedra with nickel and silver atoms at vertices and preferentially nickel atoms at centers.     

Concentration quenching and migration of excitations in a bulk Cd<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>Te crystal

The curves of intracenter luminescence decay for Mn²⁺ ions in the Cd_0.5Mn_0.5Te semiconductor solid solution, obtained in a low-temperature experiment, have been simulated by the Monte Carlo method. The features of the kinetics of the 2-eV band in the time interval where significant nonexponentiality of relaxation at different points of the emission band profile manifests itself, as well the integral kinetics and energy relaxation, have been considered. Migration of ion excitations and concentration quenching (which was previously disregarded) are considered to be the main mechanisms determining the kinetic curve formation. It was established that excitation by 2.34-eV photons leads to both selective (intracenter) and band excitation of Mn²⁺ ions. Comparison of the results of numerical simulation and experiment showed that the characteristic values of the migration and quenching rates (W _m and W _q , respectively) are close in magnitude and W _{q, m} ≈ 0.1/τ, where τ is the lifetime at the long-wavelength band wing with the exponential kinetics. The estimated quantum yield (0.56) indicates significant influence of the concentration quenching on the 2-eV luminescence quantum yield in Cd_{1 ? x} Mn _x Te and Zn_{1 ? x} Mn _x S crystals with a high concentration of Mn²⁺ ions.     

Stress relaxation and viscosity of a bulk Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> metallic glass under isochronous heating conditions

Isochronous relaxation of tensile stresses is measured in a bulk Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glass in the initial state and after certain thermal treatments. The results of measurements are used to find the energy spectrum of irreversible structural relaxation, from which the temperature dependence of shear viscosity is then calculated. This dependence is also found independently from measurements of creep in the same glass. The calculated viscosity is shown to agree well with the experimental data.     

Study of structural phase transitions in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6+δ</Subscript> by x-ray photoelectron spectroscopy

We have used x-ray photoelectron spectroscopy to investigate the charge state of oxygen found in the basal structural plane of YBa₂Cu₃O₆+γ.. We have observed a change in this state after thermal treatment, with a transition to the adjacent structural phase region. We have shown that changes in the charge state of oxygen can be used as an indicator of structural changes occurring in YBa₂Cu₃O₆+δ.. We have found that the rate of structural relaxation yttrium barium cuprate depends on the amount of structural water it contains. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 195–198, March–April, 2007.     

Acoustic attenuation in ferroelectric Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> crystals

The temperature and frequency dependencies of sound attenuation for the proper uniaxial ferroelectric Sn₂P₂S₆, which has a strong nonlinear interaction of the polar soft optic and fully symmetrical optic modes that is related to the triple well potential, were studied by Brillouin spectroscopy. It was found that the sound velocity anomaly is described in the Landau-Khalatnikov approximation with one relaxation time. For explanation of the observed temperature and frequency dependencies of the sound attenuation in the ferroelectrric phase, the accounting of several relaxation times is needed and, for quantitative calculations, the mode Gruneisen coefficients are more appropriate as interacting parameters than are the electrostrictive coefficients. Relaxational sound attenuation by domain walls also appears in the ferroelectric phase of Sn₂P₂S₆ crystals.     

Investigations of dielectric enhancement in (Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>)<Subscript>1-x</Subscript>(TiO<Subscript>2</Subscript>)<Subscript>x</Subscript> ceramics prepared by laser-sintering technique

The maximum dielectric permittivity of Ti-doped Ta₂O₅ ceramics may reach 450 by a laser-sintering technique. The aim of this study is to investigate the mechanisms of the dielectric enhancement based on the unique structural and morphological properties of the laser-sintered ceramics. The reason for the dielectric enhancement is due to the crystal structure distortion in the high-temperature phase, the oriented grain growth taking place in a direction deviating from [001] in the laser-sintered ceramics. The concurrent nature of quenching effects, a sharp temperature gradient and mass transfer in liquid phase originated from laser high energy irradiation with strict directivity leads to the structural and morphological properties. PACS 81.40.Tv; 61.80.Ba; 77.22.-d; 77.22.Ch     

Transient optical absorption induced by an electron pulse in KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript> crystals

The efficiency of formation and time evolution of radiation-induced structural defects and pulsed luminescence in KPb₂Cl₅ crystals under the action of a single electron pulse (E = 250 keV, τ = 20 ns) have been investigated. The spectra (1.1–3.8 eV) and relaxation kinetics (time interval 5 × 10^?8?5 s) of transient optical absorption and the pulsed cathodoluminescence spectra and decay kinetics (1.4–3.1 eV) have been measured in the temperature range 80–300 K. It is revealed that the induced optical density and its time evolution depend strongly on temperature, and the absorption relaxation time contains several components and reaches several seconds at T = 300 K. The decay kinetics of transient absorption and pulsed cathodoluminescence kinetics have different orders and are controlled by different relaxation processes.     

EPR Study of Sc<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Nd<Superscript>143</Superscript> Isotopically Pure Impurity Crystals

The Sc₂SiO₅ single crystals doped with 0.001 at.% of the ¹⁴³Nd³⁺ ion were studied by continuous-wave and pulse electron paramagnetic resonance methods. The g-tensors and hyperfine structure tensors for two magnetically non-equivalent Nd ions were obtained. The spin–spin and spin–lattice relaxation times were measured at 9.82 GHz in the temperature range from 4 to 10 K. It was established that three relaxation processes contribute to the spin–lattice relaxation processes. There are one-phonon spin–phonon interaction, two-phonon Raman interaction and two-phonon Orbach–Aminov relaxation processes. It was established that spin–spin relaxation time is of the same magnitude for neodymium ion doped in Sc₂SiO₅ and in Y₂SiO₅.     

Concentration quenching anomalies of activated Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Pr<Superscript>3+</Superscript> nanocrystal luminescence

For the fist time in Y₂SiO₅:Pr³⁺ nanocrystals, the ordered stage in the ¹ D ₂ luminescence decay curves for Pr³⁺ ions has been observed at anomalously low doped ion concentration (0.5 at %). This effect is caused by preferred location of the activator ions in the near-surface layer of the nanocrystal that provides the relaxation of elastic tension arising due to the difference of ionic radii of Pr³⁺ and Y³⁺ ions. Concentration quenching of Pr³⁺ luminescence is caused by the cooperative cross-relaxation.     

Electron paramagnetic resonance in a Gd<Subscript>0.14</Subscript>Si<Subscript>0.86</Subscript> amorphous film: Bottleneck regime

Electron paramagnetic resonance (EPR) in a Gd_0.14Si_0.86 amorphous film is studied over a wide temperature range from 4 to 300 K. The experimental results are analyzed with regard to the strong structural disorder in the system under study. This disorder leads to the formation of droplets, that is, regions with a high density of electronic states. It is shown that the observed EPR signal can be formed only in the double bottleneck regime, and temperature dependences are obtained for the line position and width. The spin-lattice relaxation rates for electrons and Gd ions, the second spectral moment of the line, the ferromagnetic transition temperature, the number of Gd atoms in the droplets, and the product of the electron density of states by the exchange coupling constant between electrons and Gd ions are evaluated from comparison with experimental data. The values obtained corroborate the validity of the assumptions that the double bottleneck conditions are fulfilled and structural and phase nanoscale inhomogeneities exist in the system.