We present measurements and analysis of the thermal conductivity, K(T), of the linear chain semiconductor (NbSe4)3I, which undergoes a phase transition beween two semiconducting phases at Tc=274K. The obtained data cover the range 100–340 K. The behaviour of K(T) is similar to that expected for insulating crystals, where K(T) is mainly governed by the umklapp processes. Beyond that, the thermal conductivity anomaly appears at Tc as a consequence of the structural phase transition that has been also seen in specific heat.

Pulsed laser deposition technique was employed to grow thin films of K0.3MoO3 on Al2O3 (1-102) and SrTiO3 (510) substrates. Structural and imaging characterization revealed good quality films with well oriented grains of few microns in length. Both non-selective (transport) and order-selective (femtosecond pump-probe spectroscopy) probes revealed charge density wave properties that are very close to those of the single crystals. The films exhibit metal-semiconductor phase transition in resistivity, pump-probe data show phase transition at the same temperature as the single crystal and the threshold for the photo-induced phase transition is approximately the same as in single crystal. We compare the properties of films with grains differing by an order of magnitude in length.

Recent studies (J. Alloys Compd. 695 (2017) 2661) of the electronic structure and properties of (TiZrNbCu)_1-xNi_x (x≤0.25) amorphous high entropy alloys (a-HEA) have been extended to x=0.5 in order to compare behaviours of a-HEA and conventional Ni-base metallic glasses (MG). The amorphous state of all samples was verified by thermal analysis and X-ray diffraction (XRD). XRD indicated a probable change in local atomic arrangements, i.e. short-range-order (SRO) for x≥0.35. Simultaneously, thermal parameters, such as the first crystallization temperature T_x and the liquidus temperature showed a tendency to saturate for x≥0.35 . The same tendency also appeared in the magnetic susceptibility χ_exp and the linear term in the low temperature specific heat γ. The Debye temperatures and Youngs moduli also tend to saturate for x≥0.35. These unusual changes in SRO and all properties within the amorphous phase seem correlated with the change of valence electron number (VEC) on increasing x.

The atomic structure, electronic structure, and physical properties of (TiZrNbCu)1− xNix (x ≤ 0.5) metallic glasses (MGs) were studied in both the high-entropy (0 < x < 0.35) and the higher Ni concentration range (x ≥ 0.35). Atomic structure studies performed with X-ray diffraction and synchrotron powder diffraction provided average atomic volumes, structure factors, radial distribution functions, coordination numbers, and packing densities. Electronic structure studies performed using photoemission spectroscopy and low-temperature specific heat provided information about the electronic density of states within the valence band and at the Fermi level and also about interatomic bonding and atomic vibrations [from the Debye temperature and the boson peak (BP)]. Variations of both atomic structure and electronic structure with x showed a clear change for x ≥ 0.35, which corresponds to a valence electron number ≥7.4. All physical properties, namely, thermal stability parameters, Debye temperatures, BPs, magnetic, elastic, and electronic transport properties, change their concentration-dependence for x ≥ 0.35. The results are compared with those for binary and ternary MGs of the same elements.

The atomic structure, electronic structure and physical properties of (TiZrNbCu)_(1-x)Ni_x (x ≤ 0.5) metallic glasses (MG) were studied in both the high-entropy (0<x<0.35) and the higher Ni concentration range (x ≥ 0.35). Atomic structure studies performed with X-ray diffraction and synchrotron powder diffraction provided average atomic volumes, structure factors, radial distribution functions, coordination numbers and packing densities. Electronic structure studies performed using photoemission spectroscopy and low-temperature specific heat provided information about the electronic density of states within the valence band and at the Fermi level and also about interatomic bonding and atomic vibrations (from the Debye temperature and the boson peak). Variations of both atomic structure and electronic structure with x showed a clear change for x ≥ 0.35, which corresponds to a valence electron number ≥ 7.4. All physical properties, namely thermal stability parameters, Debye temperatures, boson peaks, magnetic, elastic and electronic transport properties change their concentration-dependence for x≥ 0.35. The results are compared with those for binary and ternary MGs of the same elements.

Hard form of carbon obtained by collapsing C60 fullerene molecules at moderate pressure and temperature was investigated using different imaging techniques at spatial resolutions ranging from angstrom to millimeter. Hierarchical granular morphology has been observed from the atomic up to the sample size length scale, revealing scale independent grain size distribution. The unusual fractal-like structure correlates with unique transport and calorimetric properties of this material. Hard carbon can be considered as a bridge between porous and dense amorphous materials.

We present an experimental investigation of the fragility and heat capacity of metallic glass Zr77Ni23. The ribbon sample was produced by melt-spinning technique. Glass transition temperature T-g obtained by differential scanning calorimetry with various heating rates was used to estimate fragility parameter m. Heat capacity measurements were performed in a wide temperature interval, ranging from 1.8 K up to room temperature, for as-cast and relaxed samples in different magnetic field strengths. Our results do not show any excess of vibrational density of states over the Debye contribution corresponding to the boson peak. Relaxation of the sample causes a slight decrease of Debye contribution consistent with the measured increase of Young modulus. The fact that no boson peak is observed in heat capacity, together with the obtained intermediate fragility of m = 53, positions Zr77Ni23 well outside established correlations between fragility, boson peak strength, and glass forming ability.

A comprehensive study of selected properties of four (TiZrNbCu) 1-x Ni x (x ≤ 0.25) amorphous high entropy alloys (a-HEA) has been performed. The samples were ribbons about 20 μm thick and their fully amorphous state was verified by X-ray diffraction and thermal analysis. The surface morphology, precise composition and the distribution of components were studied with a Scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) attachment. The properties selected were the melting temperature (T m ), the low temperature specific heat (LTSH), the magnetic susceptibility χ exp and the Young's modulus (E). Whereas LTSH and χ exp were measured for the as-cast samples, E was measured both for as-cast samples and relaxed samples (after a short anneal close to the glass transition temperature). The LTSH showed that the electronic density of states at the Fermi level, N 0 (E F ), decreases with increasing x, whereas the Debye temperature (θ D ) increases with x. This is similar to what is observed in binary and ternary amorphous alloys of early transition metals (TE) with late transition metals (TL) and indicates that N 0 (E F ) is dominated by the d-electrons of the TE. The LTSH also showed the absence of superconductivity down to 1.8 K and indicated the emergence of the Boson peak above 4 K in all alloys. The free-electron like paramagnetic contribution to χ exp also decreases with x, whereas E, like θ D , increases with x, indicating enhanced interatomic bonding on addition of Ni. The applicability of the rule of mixtures to these and other similar HEAs is briefly discussed.

Dosadasnje istraživanje elektronske strukture (TiZrNbCu)1-xNix (x≤0.25) amorfnih visokoentropijskih slitina (a-HEA [1]) prosireno je do x=0.5 s namjerom da usporedimo ponasanje a-HEA i standardnih metalnih stakala (MG) s Ni. Uzorci su bile trakice oko 20 μm tanke, a amorfno stanje je provjereno termickom analizom i difrakcijom X-zraka (XRD). XRD dijagrame upotrijebili smo za izracunavanje udaljenosti najbližih susjeda i lokalnog uređenja [1, 2]. Tocniju kompoziciju i distribuciju komponenata izucavali smo sa skenirajucim elektronskim mikroskopom (SEM) s dodatkom za energijski disperzivnu spektroskopiju (EDS). Ovdje istražujemo termicke parametre (temperature staklastog prijelaza Tg, temperature prve kristalizacije Tx, temperature taljenja Tm i temperature tekuceg stanja Tl), niskotemperaturni specificni toplinski kapacitet (LTSH [1]), magnetsku susceptibilnost χexp i Youngove module E. E smo mjerili za as-cast i relaksirane trake (nakon kratkog aniliranja blizu Tg), a sva ostala svojstva mjerili smo samo na as-cast uzorcima. LTSH pokazuje da elektronska gustoca stanja na Fermijevom nivou N(EF) opada s povecanjem x, dok Debye-eva temperatura ΘD raste s x [1]. Slicno ponasanje uocili smo u binarnim i ternarnim MG [2, 3] između ranih prijelaznih (TE) i kasnih prijelaznih metala (TL) koje pokazuje da je N(EF) pretežno određena s TE d-elektronima. ΘD , E, Tx i Tl rastu s x pokazujuci porast međuatomskih veza dodavanjem Ni (slicno kao u binarnim TE-Ni MG [2, 4]). Međutim Tx i Tl teže zasicenju za x≥0.25 pa se cini da opisuju promjenu u lokalnoj strukturi oko x=0.25 koja slijedi iz analize XRD dijagrama. Uobicajeni parametri pridruženi sposobnosti ostakljivanja (GFA) pokazuju malu promjenu s x, no nema stvarne promjene u GFA kada idemo od a-HEA prema standardnim MG u promatranim sustavima. Kako smo i ocekivali [1], pravilo smjese ne daje dobar opis za mnoga svojstva nasih slitina. 1. K. Biljakovic et al, J. Alloys Compd. 695 (2017) 2661 2. R. Ristic et al, J. Alloys Compd. 621 (2015) 136 3. R. Ristic et al, Solid State Commun. 151 (2011) 1014 4. R. Ristic , M. Stubicar, E. Babic, Phil. Mag. 87 (2007) 5629

Received 21 October 2016DOI:https://doi.org/10.1103/PhysRevB.94.179904©2016 American Physical Society

We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor (NbSe4)(3)I by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a well-documented pseudo-Jahn-Teller ferrodistortive structural transition at T-C = 274 K, where the displacements of Nb ions lead to ferroelectric (FE) in-chain polarization with opposite direction in adjacent chains, all methods suggest an additional lowering of symmetry at T* approximate to 160 K. Although antiferroelectric (AFE) phase is partially formed at TC, our results consistently point to an enhancement of the interchain order at T*, thus leading to AFE order-disorder transition, as supported by the earlier dielectric and structural studies.

We present the morphology and electrical conductivity of thin films of quasi one-dimensional conductor K0.3MoO3 produced by pulsed laser deposition. Atomic force microscopy reveals granular nature of the films with the texture depending on the substrate and deposition conditions. While the films with better texture have higher conductivity, they all show universal temperature dependence in the temperature range 20 K–300 K. The results are analyzed within the models of co-tunneling variable range hopping (VRH) conductivity in granular media based on the Efros–Shklovskii (ES–VRH) model. We suggest two different approaches to interpret the data, either by two ES–VRH regimes with crossover around 45 K or by a modified ES–VRH regime with T2 pre-factor up to T ~ 100 K and an activated one above. The second approach yields a unique value of ES–VRH parameter T0 = 1000 K in all examined films.

We show that the specific heat of incommensurately modulated crystals with broken translational periodicity presents similar features at low temperatures to those of amorphous and glass materials. Here we demonstrate that the excess to the constant C_{p}(T)/T^{3} law (or Debye limit) is made up of an upturn below 1 K and of a broad bump at T≈10 K that directly originates from the gapped phase and amplitude modes of the incommensurate structure. We argue that the low-energy dynamics of incommensurate systems constitute a plausible simplification of the landscape of interactions present in glasses, giving rise to their low-temperature anomalies.

We report on the heat capacity investigation of Cu55Hf45-xTix metallic glasses. The most appropriate procedure to estimate low temperature electronic and phonon contributions has been determined. Both contributions exhibit monotonous Ti concentration dependence, demonstrating that there is no relation of either the electron density of states at the Fermi level or the Debye temperature to the increased glass forming ability in the Ti concentration range x = 15-30. The thermodynamic parameters (e. g., reduced glass temperature) remain better indicators in assessing the best composition for bulk metallic glass formation. (C) 2014 AIP Publishing LLC.