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Blending is a technique known in polymer technology that takes advantage of the processibility of polymers to produce new solid materials or composites with specific structural and physical properties, distinct from the ones of their components. In thin films of polymer blends interesting morphologies are formed because of phase separation. For conjugated polymers, i.e. solution-processible semiconductors, blending also opens a way to optimize the performance of opto-electronic devices, bringing about technological benefits. It is therefore crucial to achieve understanding of the effect film morphology has on the device performance, and, ultimately, to achieve control over the phase separation in a blend, so that structures can be designed that yield the desired device performance. Light-emitting diodes (LEDs) made of polymer blends have shown strongly enhanced electroluminescence (EL) efficiencies, as compared to pure homopolymers. Colour conversion, white light emission, polarized light emission, emission line narrowing, and voltage-tunable colours are other effects that have been observed in blends containing light-emitting polymers. Although the enhanced EL efficiency is attributed to Förster-type energy transfer in numerous reports, the exciton dynamics behind this effect is not well understood. Here we review the formation and morphology of thin films of conjugated polymer blends, as well as modern microscopic and spectroscopic techniques to study them. Furthermore, we attempt to link the film morphology to the electronic performance of electroluminescent and photovoltaic devices and discuss energy and charge transfer phenomena at the interfaces. We also report some new results, specifically for polyfluorene blends in LEDs.

This article was originally intended for publication in Issue 42 of this volume, which was a special issue on Conjugated Polymers: Issue 42

We report measurements of the anisotropy in the photophysics of an oriented dendritic side group conjugated phenylenevinylene polymer. The essential features of the absorption and emission can be understood in terms of the contribution of two morphological regions in the film, one being relatively highly ordered. The ordered regions have spectroscopy like that of polymers with sterically hindered torsion and good luminescence yield. Surprisingly, we present evidence that their emissive efficiency is lower when they are excited directly than through energy transfer from disordered regions. We also observe long-lived emission with transition dipole perpendicular to the chain orientation that is suggestive of charge transfer exciton emission from the ordered regions of the sample.

This article was originally intended for publication in Issue 42 of this volume, which was a special issue on Conjugated Polymers: Issue 42

This paper was originally accepted as a Topical Review but published, in error, as a regular article.

We compute the DC conductance for a homogeneous sine–Gordon model and an impurity system, which in the conformal limit can be reduced to a Luttinger liquid, by means of the thermodynamic Bethe ansatz and standard potential scattering theory. We demonstrate that unstable particles and resonances in impurity systems lead to a sharp increase of the conductance as a function of the temperature, which is characterized by the Breit–Wigner formula.

The magnetic susceptibilities of a series of compounds, β'-X[Pd(dmit)₂]₂ (X = Me₄As, Me₄P, Me₄Sb, Et₂Me₂P, and Et₂Me₂Sb, where Me = CH₃ and Et = C₂H₅), have been investigated. The temperature dependence of χ has been analysed in terms of the two-dimensional spin-1/2 Heisenberg antiferromagnet on the triangular lattice; it is the first time that this approach has been applied to experimental data. The observed χ can be understood as reflecting the behaviour of the geometrically frustrated spins. The variation among the compounds suggests a role of frustration in relation to the relative stability of the metallic state.

The surface energy (SE) for mercury was calculated on the basis of the free electron model in which the electron density parameter, r_s, for bulk electrons was calculated from the density of mercury while the electron density parameter for surface electrons, r_ss, was assumed to be higher by a factor that is linearly dependent on temperature. Ideal agreement of calculated SE values with experimental data was attained for the temperatures 0–250^°C assuming that r_ss = r_s × 1.0021^T/100°C.

The structural properties of epitaxial L1₀ ordered FePt(001) films, grown by molecular beam epitaxy (alternating deposition of Fe and Pt atomic layers) on buffer-Pt/seed-Fe/GaAs(001) have been studied by in situ reflection high-energy electron diffraction and by ex situ x-ray scattering as a function of the growth conditions. Reflection high-energy electron diffraction intensity oscillations measured during FePt layer growth provide evidence for island growth at T_s = 200^° C and quasi layer-by-layer growth at T_s = 350^° C. From small-angle and wide-angle x-ray scattering it was found that the degree of epitaxy depends critically on morphology of the seed layer and the substrate roughness. X-ray diffraction analysis showed that the long-range order parameter increases from near zero for films grown at 200^°C to 0.65 for films grown at 350^°C. This confirms the fact that the order parameter is mainly determined by the surface mobility of the atoms which is controlled experimentally by the substrate temperature.

The elastic properties of both polycrystalline and epitaxial PbTiO₃ (PTO) thin films are studied using Brillouin scattering spectroscopy. The epitaxial PTO films were prepared by pulsed laser ablation on (1) a [0 0 1] single crystal of SrTiO₃ (STO) doped with Nb and (2) a [0 0 1] STO buffered with a layer of YBa₂Cu₃O₇. The polycrystalline PTO films were prepared by sol–gel on a Si substrate buffered with TiO₂ and Pt layers. The data analysis takes into account the ripple and the elasto-optic contributions. The latter significantly affects the measured spectra since it gives rise to a Love mode in the p–s scattering geometry. At room temperature, the spectra of the epitaxially grown samples are interpreted using previously published elastic constants of PTO single crystals. Sol–gel samples exhibit appreciable softening of the effective elastic properties compared to PTO single crystals: this result is explained by taking into account the random orientation of the microscopic PTO grains. For both the polycrystalline and the epitaxial films we have determined that the piezoelectric terms do not contribute to the spectra. The temperature dependence of the spectra shows strong anomalies of the elastic properties near the ferroelectric phase transition. Compared to the bulk, T_C is higher in the sol–gel films, while in the epitaxial films the sign of the T_C shift depends on the underlying material.

An experimental and theoretical comparative study of InAs quantum dots grown on (001) and (113)B InP substrates is performed. The difference between the optical transitions in the dots on the two substrates is attributed to strain effects. The influence of the first InP capping layer is also studied.

The discrete variational method in density functional theory was employed to perform first-principles electronic structure calculations for embedded clusters representing thin films of face-centred-cubic Fe on a Cu(001) substrate. 3, 4 and 5 ML of Fe were investigated; the ferromagnetic and several types of antiferromagnetic spin configurations were considered. Layer-by-layer calculations of the contact and dipolar components of the magnetic hyperfine field are reported, as well as electric-field gradients at the surface and interface layers. Significant field gradients were found at the surfaces. Clusters modelling the interdiffusion of Fe and Cu between two layers at the interface were also investigated, to determine the effects on the properties.

We report the structural and magnetic properties of Ni films grown on GaAs(001) using electrodeposition, covering the thickness range 0–80 nm. The structure is characterized by mixed (001) and (011) epitaxial orientation of fcc Ni with a preference for the Ni(001) orientation. The magnetic anisotropy is originated by a combination of a crystalline contribution with fourfold symmetry and a uniaxial anisotropy probably caused by the asymmetry in the substrate surface structure. The saturation magnetic moment varies linearly with thickness, indicating limited intermixing between Ni film and GaAs substrate. This is ascribed to the low-energy deposition process characteristic of electrodeposition.

Magnetic domains, microstructure and magnetic properties of highly oriented barium ferrite thin films with perpendicular anisotropy have been investigated with magnetic force microscopy (MFM), VSM, SEM and TEM. Two kinds of magnetic domain are energetically favourable: (a) cluster-like structure in as-deposited films grown at 770^°C; (b) stripe domains in layers annealed at high temperature (900^°C). Such a difference in domain configuration can be related to microstructure. Small single-domain grains (70 nm) exist in as-deposited films whereas annealed films consist of large multidomain platelets. The magnetic measurements (hysteresis loops and virgin curves) reveal that magnetization reverses by rotation and wall motion for cluster-like and stripe domains respectively. A good agreement was established between the domain width measured by MFM and that predicted by using the Kooy–Enz model (Kooy C and Enz U 1960 Philips Res. Rep.15 7) in our stripe structure. The analyses of minor loops and virgin curves suggest that the coercivity in stripe domains is controlled by wall nucleation rather than pinning.

We present a new investigation of the metastable 1 × 1 and reconstructed 5 × 1 phases of Ir(100) using quantitative low-energy electron diffraction and scanning tunnelling microscopy. It is shown that the 5 × 1 reconstruction of Ir(100) extends up to the fourth layer into the surface. This structural information is retrieved by the use of electron energies up to 600 eV which simultaneously provides an unusually broad database of more than 10.000 eV. Together with an excellent quality of the theory–experiment fit equivalent to an R-factor of R_P = 0.144 this allows for rather small error limits of the as many as 17 structural parameters describing the four-layer reconstructed surface. Similar features hold for the 1 × 1 phase which is analysed in parallel. In addition, we present a systematic investigation of the influence of the electron energy range applied and of the allowed depth of reconstruction on the accuracy of the analysis. It appears that for the case of Ir(100)-5 × 1 the structural parameters describing the top two layers are largely independent from the consideration of the reconstruction of deeper layers.

In the resonant Raman scattering (RRS) process the emitted photon exhibits a continuous energy distribution with a high energy cutoff limit. This cutoff energy depends on the chemical state of the element under examination. In the present work, the possibility of identifying the chemical state of V atoms by employing RRS spectroscopy with a semiconductor Si(Li) detector is investigated. A proton induced Cr Kα x-ray beam was used as the incident radiation, having a fixed energy lower than the V K-absorption edge. The net RRS distributions extracted from the energy dispersive spectra of metallic V and its compound targets were simulated by an appropriate theoretical model. The results showed the possibility of employing RRS spectroscopy with a semiconductor detector for chemical speciation studies.

Single crystals of 0.5% Cr³⁺-doped Cs₂NaGaF₆ were studied by means of x-ray diffraction and polarized Raman scattering. The crystal exhibits a unique stacking interaction, with a hexagonal structure with Rm symmetry. Polarized Raman spectra recorded at 16 and 300 K reveal sidebands that are ascribed to the local vibrational of the [CrF₆] coordination unit, which differ markedly from those of the Cs₂NaGaF₆ host lattice. The results are compared to findings for other elpasolite lattices, and the room temperature luminescence quantum yields are discussed in terms of a delicate balance between electron–phonon strength and lattice distortion.

Powder neutron diffraction and Mössbauer spectral studies have been carried out on Nd₆Fe₁₃Si between 2–295 K. The nuclear neutron scattering shows that Nd₆Fe₁₃Si has the tetragonal I4/mcm crystal structure at all temperatures. A collinear antiferromagnetic structure with the wavevector q = (0, 0, 1) is observed below the Néel temperature of 421 K. A spin reorientation is observed at ∼100 K in both the neutron diffraction patterns and the Mössbauer spectra. Above and below 100 K, the magnetic moments of the four iron and the two neodymium crystallographic sites are ferromagnetically coupled within one block along the c axis and the resulting magnetic moment of this block is antiferromagnetically coupled with that of the adjacent block along the c axis through a layer of silicon atoms. Above and below 100 K, the magnetic moments are found to be parallel or very close to the c axis and within or close to the (a, b) basal plane of the tetragonal unit cell, respectively. This first-order spontaneous zero-field spin reorientation occurs cooperatively and involves both the neodymium and iron magnetic moments. The powder neutron diffraction between 10 and 200 K indicates anisotropic lattice changes associated with a change in the magnetoelastic coupling in this compound. The Mössbauer spectral hyperfine parameters are those expected for axial and basal magnetization directions in Nd₆Fe₁₃Si and further indicate the existence of a 75% basal and 25% axial mixed magnetic phase even at 4.2 K, a mixed magnetic phase which results from the influence of the secondary ferromagnetic Nd₂Fe₁₇ phase on the primary Nd₆Fe₁₃Si phase.

The non-linear dynamics involved in sliding modes in an incommensurate composite is studied in the double chain model. The coupling between the chains leads to phonons in which the two chains participate in various ways. For displacements beyond the harmonic approximation it is shown that, for a coupling small enough to leave the modulation functions continuous, there is a dynamic transition from a practically frictionless regime to a regime with strong dissipation. In the cross-over region resonances lead to an oscillatory motion of the subsystems with respect to each other. In the regime of discontinuous modulation functions there is strong dissipation and a transition from a pinned to an unpinned state. The unpinned motion is a non-linear wave in superspace.

Structural changes in the cubic spinels CdCr_2−xGa_xSe₄ have been studied by means of single-crystal x-ray diffraction at low temperature and energy-dispersive diffraction in a diamond-anvil cell at high pressure. In stoichiometric samples (x = 0), a spontaneous magnetostriction reduces the thermal expansion coefficient from 6.7 × 10⁻⁶ K⁻¹ in the paramagnetic phase to 2.2 × 10⁻⁶ K⁻¹ in the ferromagnetic phase (T_C = 130 K). In the samples with Ga³⁺ admixtures (x = 0.06 and 0.12), a slight structural distortion causes an order–disorder-type phase transition at T_d ≈ 285 K connected with changes in the electronic configuration of the Jahn–Teller-active Cr cations. The magnetostriction is apparently not very sensitive to the Ga³⁺ admixtures in the present concentration range. At high pressure the cubic unit cell transforms to a tetragonal one with c/a = 0.91. The Jahn–Teller effect is combined with the rocking motions of corner-sharing metal coordination polyhedra, altering their shape. The transition pressure is about 10 GPa. The bulk modulus of the cubic phase is B₀ = 103 GPa.

A cluster calculation of hyperfine coupling constants based on density functional theory (DFT) has been performed for the carbon ⟨100⟩ split interstitial (V_C + 2C) in various charge and spin states in cubic SiC along with the dihydrogen-containing defect (V_C + 2H). Compared to the isolated carbon vacancy, the presence of two carbon atoms in the split interstitial centre causes lowering of the point symmetry for positive and negative charge states from D_2d to D₂ and substantially reduces the spin density on the nearest Si neighbours. The DFT-based approach has been used for a calculation of the zero-field splitting parameters D and E of the neutral (V_C + 2C)⁰ state with spin S = 1. Singly charged and neutral carbon ⟨100⟩ split interstitial defects are suggested as a microscopic model of the well-known T5 (initially identified as V_C⁺ and then re-identified as a dihydrogen-containing complex) and EI3 centres in SiC, respectively.

We have studied the electronic structure of three-dimensional transition-metal–MgB₂ alloys, Mg_0.97TM_0.03B₂, (TM = Sc, Ti, V, Cr Mn, Fe, Co, Ni, Cu, Zn) using the Korringa–Kohn–Rostoker coherent-potential approximation method in the atomic-sphere approximation. For unpolarized calculations, our results for Mg_0.97TM_0.03B₂ alloys are similar to that of 3d impurities in other s and s–p metals. In particular, the local densities of states (DOS) associated with the 3d impurities are similar to our earlier work on 3d impurities in bulk Al (Singh P P 1991 Phys. Rev. B 43 3975; Singh P P 1991 J. Phys.: Condens. Matter3 3285). For spin-polarized calculations, we find only the alloys of V, Cr, Mn, Fe and Co with MgB₂ to be magnetic of all the 3d elements. We also find that Cr and Mn in MgB₂ have a relatively large local magnetic moment of 2.43 and 2.87μ_B, respectively. We have used the unpolarized, self-consistent potentials of Mg_0.97TM_0.03B₂ alloys, obtained within the coherent-potential approximation, to calculate the electron–phonon coupling constant λ using the Gaspari–Gyorffy formalism and the superconducting transition temperature T_c using the Allen–Dynes equation. We find that the calculated T_c is lowest for Mg_0.97Cr_0.03B₂ and highest for Mg_0.97Zn_0.03B₂, in qualitative agreement with experiment. The calculated trend in variation of T_c from Mn to Zn is also similar to the available experimental data. Our analysis of the variation in T_c, in terms of the DOS and the spectral function along the Γ to A direction, shows the variation to be an interplay between the total DOS at the Fermi energy and the creation/removal of states along the Γ to A direction (Singh P P 2002 Preprint cond-mat/0201093).

Experiments aimed at the stabilization of the metastable face-centred-cubic (fcc) phase of Mg which was found by calculation of the epitaxial Bain path (EBP) are described. Ultrathin films of Mg up to 14 Å thick are grown on a W{001} substrate and found to be pseudomorphic. A quantitative low-energy electron diffraction analysis finds the crystal structure of these films to be body-centred tetragonal with axial ratio c/a = 1.39. Consideration of where this structure fits on the calculated EBP confirms that it is a strained state of the fcc phase, which has therefore been stabilized by pseudomorphic epitaxy.

The collective properties of indirect excitons in coupled quantum wells (CQWs) are considered. The energy of the ground state of the exciton liquid as a function of the density of electrons e and holes h at different separations D between e and h layers is analysed. The quantum gas–liquid transition as D decreases is studied. The superfluidity appearance temperatures in the system (Kosterlitz–Thouless transition temperatures) have been estimated at different separations D between e and h layers. For the anisotropic two-dimensional e–h system in CQWs the Mott metal–insulator quantum transition is considered. The instability of the ground state of the system of interacting two-dimensional indirect excitons in a slab of superlattice with alternating e and h layers is established. The stable system of indirect quasi-two-dimensional biexcitons, consisting of indirect excitons with opposite directed dipole moments, is considered. The radius and the binding energy of the indirect biexciton are calculated. The collective spectrum of a rare system of two-dimensional indirect biexcitons, interacting as electrical quadrupoles, is studied. The density of the superfluid component n_s (T) and the Kosterlitz–Thouless phase transition to the superfluid state in this system are analysed.

We study the effect of Coulomb correlation on the transmission properties of a one-dimensional chain connected to two perfect leads in the presence of a static magnetic field. Due to the presence of a strong on-site nonlinear interaction between two opposite spins within the chain, the zero-voltage conductance exhibits strong correlations between parallel and antiparallel spin conduction channels which results in a substantial spin polarization for small chain sizes.

A new way of solving the non-linear secular equation within the augmented plane wave (APW) method is presented. The traditional computation of the APW secular determinant is replaced by a scheme where we follow the eigenvalues of the secular matrix for a number of energies. These eigenvalues, referred to as the meta-eigenvalues of the original APW problem, provide more information about the system for each energy examined than just their product, i.e. the value of the secular determinant. The new scheme for finding the APW eigenvalues can be made considerably more efficient than the traditional one, and is useful in calculations where a linearized approximation to the APW secular matrix is insufficient, such as for optical calculations extending over a wide energy range or for energy dependent effective potentials.

We prepared a set of polycrystalline samples of the thermoelectric oxide NaCo_2−xPd_xO₄ (x = 0, 0.05, 0.1, and 0.2), and investigated the Pd substitution effects on transport phenomena. The effects are so drastic that just 5–10% Pd ions reduce the resistivity and the Seebeck coefficient to one third of the values for x = 0, and increase the magnitude of the Hall coefficient by three times. A semi-quantitative analysis has revealed that the x = 0.2 sample has much smaller effective mass and carrier concentration than the x = 0.05 sample. This is difficult to explain within a rigid-band picture, and is qualitatively consistent with a strong-correlation picture applied to the Ce-based heavy-fermion systems.

The structural, magnetic and transport properties of the compounds Sr₂(Fe_1−xMn_x)MoO₆ (0 ≤ x ≤ 0.45) have been studied. The saturated magnetization, Curie temperature and low-field magnetoresistance of the compounds decrease with x, while the resistivity increases by several orders of magnitude when x exceeds a critical value. A positive magnetoresistance has been observed for x = 0.45. A possible percolation mechanism is proposed to elucidate the observations; it also suggests a coexistence of (Mn³⁺, Mo⁵⁺) and (Mn²⁺, Mo⁶⁺) valence pairs and a saturated substitution of Mn³⁺ for Fe³⁺.

In this paper we present a formalism for the calculation of electron transport through three-terminal junction devices, which have received attention due to their recently demonstrated non-linear electrical properties. The formalism, which is based on the scattering-matrix method, takes quantum interference effects fully into account. Furthermore, the formalism provides numerical stability in the calculations as well as large flexibility in the modelling of arbitrary potential profiles due to the common basis approach used in the formulation. The method is used to calculate the transport properties for Y-shaped three-terminal ballistic junction (TBJ) structures with configurations typical of recently performed experiments. Quantum interference effects are shown to strongly influence the transport characteristics of TBJ structures due to complex scattering of the electrons in the cavity-like coupling window between the three arms of the device. The theoretical approach presented in this paper provides a flexible tool for the study of such quantum interference effects, which may play an important role in the design and functionality of future nanoscale devices based on three-terminal junctions.

The EPR (electron paramagnetic resonance) spectra of non-Jahn–Teller (JT) Mn²⁺ and JT Cu²⁺ ions have been studied for α- or β-LAS structure modification in the temperature range of 4.2–480 K. The experimental evidence for JT glass with frozen-in random strain fields due to the presence of the JT Cu²⁺ ions is presented.

The influence of a magnetic field on the hole energy spectra of uniform and multilayer semiconductor nanocrystals is studied. The calculations are performed within the k · p method and envelope function approximation. The valence subband mixing is taken into account by considering a four-band Hamiltonian. It is found that the influence of a magnetic field depends strongly on the nanocrystal size and composition. Several phenomena, reported recently for electrons in multishell nanocrystals in a magnetic field, like crossover from confinement in the external shell to the internal core in quantum dot quantum barrier structures or spatial polar separation of the charge density in quantum dot quantum well systems, are also observed for holes. The calculated optical electron–hole transitions in small uniform spherical nanocrystals reveal that the δ_lL, selection rule, forbidding at B = 0 electron–hole transitions between states of different orbital angular momentum, is also approximately fulfilled, even at strong magnetic fields.

A theoretical model is suggested that describes the effects of misfit stresses on defect structures, phase content and critical transition temperature T_c in high-T_c superconducting films. The focus is placed on the exemplary case of YBaCuO films deposited onto LaSrAlO₄ substrates. It is theoretically revealed here that misfit stresses are capable of inducing phase transformations controlled by the generation of misfit dislocations in growing cuprate films. These transformations, in the framework of the suggested model, account for experimental data on the influence of the film thickness on phase content and critical temperature T_c of superconducting cuprate films, reported in the literature. The potential role of stress-assisted phase transformations in suppression of critical current density across grain boundaries in high-T_c superconductors is briefly discussed.

Magnetization measurements and Mössbauer spectrometry have been performed on La_0.7Sr_0.3Mn_1−xFe_xO₃ (x = 0.01, 0.05, 0.1, 0.2, 0.30), to clarify the local magnetic order around Fe³⁺ ions. As Mn atoms are substituted for with Fe, the magnetic structure dramatically changes, because the ferromagnetic double-exchange chain is broken. At 4.2 K all compounds are magnetically ordered with large hyperfine fields. For x = 0.05 ferromagnetic and paramagnetic phases coexist over a large temperature range. Magnetic ordering occurs in a double step. Superparamagnetic effects are observed, and can explain part of this atypical ordering process, but there is evidence of segregation and clustering of Fe, even at this low concentration.

The magnetic properties of superlattice films with alternating Fe thicknesses, Fe(3 ML)/V(y ML)/Fe(2 ML)/V(y ML) with 4 ≤ y ≤ 15, prepared by dc magnetron sputtering on MgO(001) substrates are studied by superconducting quantum interference device measurements. By investigating the basic magnetic observables of the films: the transition temperature T_c, the magnetic remanence M_r, and the saturation field H_s, which change in a correlated manner as a function of the vanadium spacer thickness, y, we find antiferromagnetic (AFM) coupling in Fe(3 ML)/V(y ML)/Fe(2 ML)/V(y ML) for 9 < y < 11. The derived values of the spin wave parameter B and the ground state magnetic moment m_s0 also change synchronously with T_c, M_r, and H_s. The peak of the AFM coupling energy per unit area, I, is estimated to be ≈ 0.06 mJ m⁻² using the H_s versus y dependence.

Neutron diffraction, ac magnetic susceptibility and magnetization measurements have been performed to study the magnetic properties of Ce-doped La_0.7Ce_0.15Ca_0.15MnO₃. A slightly distorted monoclinic P 2₁ /c symmetry for the crystal structure was found to describe the high-resolution powder diffraction pattern, taken at room temperature, better than the normally used orthorhombic Pnma symmetry does. Three anomalies, at around 165, 105 and 38 K, were clearly evident in the ac susceptibility measurements. Neutron diffraction measurements then confirmed that the anomaly at high temperature is associated with the ferromagnetic ordering of the Mn spins, whereas the low-temperature one corresponds to the ordering of the Ce spins. The ordering temperatures for the Mn and Ce spins were found to be at T_C (Mn) 180 K and T_C (Ce) 45 K, respectively, with a saturated moment of ⟨μ_z ⟩ = 2.54(5)μ_B for the Mn spins and an average moment of 0.27(3)μ_B on the rare-earth sites.

The crystallization of amorphous Sm_xFe_80−xB₂₀ melt spun ribbons is studied over an extended range of composition (0 < x < 8). Differential scanning calorimetry scans reveal different endo- and exothermic effects depending upon the composition. X-ray diffraction and Mössbauer studies for samples annealed at temperatures close to the onset of the first exothermic effect prove that, during the primary crystallization of the amorphous ribbons, both α-Fe and Fe₃B phases appear—with Sm ions randomly accommodating the Fe sites in the tetragonal Fe₃B lattice—while the subsequent exothermic reactions correspond to the decomposition of the metastable Fe₃B phase into α-Fe and Fe₂B and to the formation of the ternary Sm_1.1Fe₄B₄ phase. Fully crystallized ribbons with Sm contents lower than about 7 at.% show the co-existence between α-Fe and Fe₂B soft magnetic phases and the Sm₂Fe₁₄B magnetic one. The enhancement of magnetic properties with increasing relative proportion of magnetic phase is discussed and correlated with exchange coupling and spin wave stiffness data obtained from the magnetic measurements.

The structural, magnetic and electronic properties of the double perovskite series Sr₂FeMo_1−xW_xO₆, where x = 0, 0.1, 0.2, 0.3 and 0.4, are investigated using x-ray diffraction, Mössbauer spectroscopy and magnetization measurements. The crystal structure has been studied at 450 K and at room temperature. There is a structural transition from tetragonal to cubic for x ≤ 0.2. The Curie temperature (T_C) shows a slight increase for x = 0.1 and 0.2 (T_C = 435 and 432 K, respectively), compared to the value (T_C = 415 K) of the x = 0 end member. The largest magnetoresistance at 300 K was found for the x = 0 and 0.2 compounds. The concentration of antisite defects determined by Mössbauer spectroscopy and x-ray analysis indicate that: (i) cation ordering at the B sites improves with increasing W content and (ii) the antisite defects formed in the B sites of the double perovskite structure do not aggregate to form bigger intragrain clusters with different local chemical compositions. The x dependence of the magnetic moment, which exceeds 4μ_B per formula unit when x > 0.3, is explained in a ferrimagnetic model with, respectively, antiparallel and parallel coupling of antisite iron and molybdenum to their iron or molybdenum cation neighbours. There is a small contribution of 0.2 μ_B/W to the ↓ sublattice moment. The W-containing materials are not half-metallic.

The double perovskite Ba₂FeMoO₆ has been studied by neutron powder diffraction, Mössbauer spectrometry and x-ray absorption spectroscopy, and is compared with Sr₂FeMoO₆. It is shown that the size of the A-site cation has a large effect upon the nature of the low-temperature state, favouring the majority Fe²⁺/Mo⁶⁺ pair in the case of barium and the Fe³⁺/Mo⁵⁺ pair in the case of strontium. In both cases, an electronic transfer appears as T decreases, interpreted as the existence of a minority t_2g ↓ narrow band, where the electron is itinerant.

A high-pressure Raman study of SrWO₄ reveals a pressure induced phase transition starting at 11.5 GPa. Several Raman lines exhibit a nonlinear behaviour in the pressure range of 11.5–15 GPa, which can be attributed to either stabilization of the high-pressure phase or an intermediate phase. Using a theoretical lattice dynamical calculation, based on an empirical potential model, we have obtained the Raman active mode eigenvectors giving us an insight into the phase transition mechanism. The lowest-frequency mode exhibits a negative pressure slope in the scheelite phase and involves a motion of the WO₄ tetrahedron as a whole according to the theoretical results. The experimental evidence suggests that the structure of the high-pressure phase is closely related to the scheelite structure, being formed by closely lying distorted WO₄ tetrahedra rather than involving an octahedrally coordinated W ion.

The photoluminescence (PL) of ZnO nanoparticles loaded into porous anodic alumina (PAA) hosts has been investigated. These ZnO/PAA composites are synthesized by soaking the PAA films in an aqueous solution of zinc acetate and then annealing them at 500^°C. An intense blue PL emission peaked around 450 nm was observed after ZnO nanoparticles were loaded into the blank PAA hosts. Investigation results reveal that the singly ionized oxygen vacancies of ZnO nanoparticles are responsible for the 450 nm PL emission. This stable photoluminescent system with the blue emission wavelength (450 nm) shows promise for use in the field of light-emitting devices.

The temperature dependences of the orange and blue emissions in 10, 4.5, and 3 nm ZnS:Mn nanoparticles were investigated. The orange emission is from the ⁴T₁–⁶A₁ transition of Mn²⁺ ions and the blue emission is related to the donor–acceptor recombination in the ZnS host. With increasing temperature, the blue emission has a red-shift. On the other hand, the peak energy of the orange emission is only weakly dependent on temperature. The luminescence intensity of the orange emission decreases rapidly from 110 to 300 K for the 10 nm sample but increases obviously for the 3 nm sample, whereas the emission intensity is nearly independent of temperature for the 4.5 nm sample. A thermally activated carrier-transfer model has been proposed to explain the observed abnormal temperature behaviour of the orange emission in ZnS:Mn nanoparticles.