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Despite a huge expansion of research on compositionally complex alloys, CCA (such as the entropy alloys, HEA and the corresponding glassy alloys) their comprehension is still limited, which is detrimental both for the design of CCAs and for their application. The broad compositional range in CCAs enables simple tuning of their properties by varying the contents of their constituent elements. Accordingly, the study of transition from CCA to conventional alloy, CA composed from the same constituents is important, both for understanding the formation of solid solutions in CCAs and for proper evaluation of their potential with respect to that of CAs. However, this transition has so far been studied systematically in only two types of alloys: isopleths of the Cantor alloy and glassy TiZrNbCuNi/Co alloys with variable Co, Ni or Cu content (Materials 14 (2021) 5824 and ref. therein). In both alloy systems the variation of a given property with composition depends sharply on the selected principal component and can be either monotonic (like that in the ideal solid solution) or non-monotonic. When the variation is non- monotonic, the maximum value of the selected property is usually outside of HEA composition range.

The one-dimensional (1D) electronic systems are a fascinating subject of scientific c research because when con ned to one dimension, itinerant electrons undergo transitions to different types of collective ground states. A common example of such transition is Pierls transition from a high- temperature metallic state to a low-temperature charge density wave (CDW) semiconducting state, due to strong electron-phonon coupling. Halogenated transition metal tetrachalcogenides of the (MX4)nY family (M = Nb ; Ta ; X = S ; Se ; Y = I ; Br) provide a typical example of 1D compounds that can potentially undergo CDW transition and exhibit nonlinear transport properties. To explore those properties we can employ a range of di erent experimental techniques. Among them, dielectric spectroscopy is an appropriate technique for investigation of dynamics of the phase degree freedom in CDW systems. However, to have a complete understanding of the dynamical properties of the material it is important to obtain the information from several complementary experiments. In this seminar, I will present transport and spectroscopic (pump-probe and dielectric) studies on the halogenated niobium tetraselenide, (NbSe4)3I. It is the only representative of 1D halogenated transition metal tetrachalcogenides which does not undergo typical Pierls transition into the CDW ground state. Instead, a structural ferrodisortive transition without a noticeable appearance of the superstructure has been observed. In addition to the properties of the equilibrium state, I will also present some unpublished results of photoinduced metastable states in this compound.

M-type barium hexaferrites from the (Ba, Pb)Fe12O 19 family show a dramatic influence of lead-doping on dielectric, magnetic, as well as optical properties. The parent compound BaFe 12 O 19 is a well-known semiconducting ferrimagnet with broad range of application. On the other hand, the PbFe 12 O 19 material shows both ferromagnetic and ferroelectric properties above the room temperature. Spin and charge of iron ions within the structure of this system suggest there might a coupling between magnetic and dielectric excitations. We report on our investigation of dynamic magnetic and dielectric properties on single- crystalline lead-substituted hexaferrite (Ba, Pb)Fe 12 O 19 . On the basis of ac magnetic susceptibility and dielectric spectroscopy in radio-frequency range and low temperatures we show that the presence of lead in (Ba, Pb)Fe 12 O 19 , as compared to pristine BaFe 12 O 19 , leads to emergence of pronounced relaxations both in dielectric and magnetic sector. Their characteristic relaxation times and activation energies are similar which suggests a bi- relaxor nature of the chosen composition of (Ba, Pb)Fe 12 O 19 . We discuss the dispersion of these relaxations and their origin in the context of magnetic domains walls and the influence of doping on the crystal lattice dynamics of the M-type barium hexaferrite. This work was supported by the Russian Ministry of Education and Science Project 5-100 and Croatian Science Foundation projects IP-2013-11-1011 and IP-2018-01-2730. References: rd [1] L. Alyabyeva et al., Proceedings of the 43 International Conference on Infrared Millimeter and Terahertz Waves (IRMMW-THZ) (2018) [2] S. E. Rowley et al., Scientific Reports 6, 25724 (2016). [3] S. E. Rowley et al., Phys. Rev. B 96, 020407(R) (2017). [4] E. S. Zhukova et al., Solid State Sciences 62, 13 (2016). [5] G. L. Tan and W. Li, J. Am. Ceram. Soc. 98, 1812 (2015).

We have studied low temperature specific heat (LTSH) in different glass-forming metallic alloys: binary marginal glasses ZrNi [1], bulk metallic glasses CuHfTi [2] and high entropy metallic glasses TiZrNbCuNi(Co) [3]. The results concerning so-called boson peak (BP) contribution to the density of vibrational states in excess to the Debye contribution are quite varied between these alloys. While Zr77Ni23 does not show BP, in Cu55Hf45- xTix its position and amplitude vary monotonously with the Ti content, Fig. 1. In TiZrNbCuNi(Co) alloys with multiple principle elements, the position of BP scales roughly with the Debye temperature, while its amplitude shows more complex behaviour. We discuss these results in respect of the intrinsic differences between these alloys [4] and in the view of different theories of BP, see e.g. [5, 6]. [1] A. Salčinović Fetić et al., Phys. Rev. B 96 (2017) 064201. [2] G. Remenyi et al., Appl. Phys. Lett. 104 (2014) 171906. [3] E. Babić et al., J. Mater. Res. 33 (2018) 3170. [4] W. H. wang, JOM 66 (2014) 2076. [5] T. Brink et al., Phys. Rev. B 94 (2016) 224203. [6] M. Baggioli and A. Zaccone, Phys. Rev. B 122 (2019) 145501.

Single crystalline lead-substituted barium hexaferrite compounds are studied in a broad spectral range, 10^2 Hz to 2*10^14 Hz. We observe excitations of different nature including dielectric and magnetic relaxations coexisting within the same frequency and temperature ranges and electronic transitions between the fine-structure components of the split Fe2+ ground state level.

We have investigated correlation between thermodynamic parameters given by low- temperature heat capacity (Cp) measurements and glass forming ability (GFA) of NiZr and CuHfTi metallic glasses. Cp of metallic glasses at sufficiently low temperature deviates from the Debye T3 law with a very well known anomaly named Boson peak (BP) which can be observed as a wide peak in Cp/T3(K) approximately at 10 K. Cp measurements were conducted in wide temperature range from 1.8 K to 300 K for as cast and relaxed Ni23Zr77 and Cu55Hf45-xTix (x=0, 5, ... and 45) samples. BP, given as subtraction of the measured Cp and sum of the Debye phonon and electronic contributions, surprisingly in NiZr sample having a low GFA was not detected [1]. Low temperature phonon and electronic contributions to Cp of CuHfTi system depend monotonically on Ti concentration (x), same as reported before [2], but BP has pronounced maximum for Ti concentrations with enhanced GFA. Finally, we can conclude that GFA can be related with low temperature properties of alloys and the strength of BP could be a measure of GFA for metallic glasses produced under the same conditions [3]. [1] A. Salčinović Fetić et al., Phys. Rev. B 96, 064201 (2017) [2] G.Remenyi, et al., Appl. Phys. Lett. 104, 171906 (2014) [3] D. Starešinić, A. Salčinović Fetić, G. Remenyi, I. A. Figueroa, E. Babić, K. Biljaković, Can intensity of BP be a measure of GFA?, under preparation

International audience

High-entropy alloys (HEA) are new type of alloys based on multiple (≥5) principal alloying elements [1). This design enables research and probable exploitation of a huge number of new alloys with structures and properties which can hardly be anticipated [2]. For obvious reason and also due to often inadequate strategy of research [3], the conceptual understanding of HEA is quite limited which hampers their development. After brief introduction in HEA we present main results of a parallel study of local atomic structure, electronic structure (including first ever photoemission spectroscopy study of HEA) and selected properties of (TiZrNbCu)1-xNix (x≤0.5) amorphous alloys, which sheds more light into their interrelationship and also enables direct comparison of HEA with conventional Ni-rich alloys (x≥0.35). Our results challenge some myths commonly employed in descriptions of HEA [2]. [1] B. Cantor, I. T. H. Chang, P. Knight, A. J. B. Vincent, Mat. Sci. Eng. A 375-377 (2004) 213. [2] E. J. Pickering, N. G. Jones, Inter. Mater. Rev. 61 (2016) 183, and references therein. [3] K. Biljaković et al , J. Alloys Compd. 695 (2017) 2661.

In the last decade, we have produced several series of thin films of charge density wave (CDW) system K0.3MoO3 by pulsed laser deposition [1-4]. Films have granular structure with typically sub- micron grain size, resulting in somewhat suppressed CDW transition and electric conductivity governed by the variable range hopping mechanism. Recently, for the first time, we have obtained an order of magnitude longer (2-4 m) and well patterned grains, as shown by AFM images in the Figure 1. Electrical conductivity and femtosecond pump- probe response in these films exhibit significant similarity with bulk samples, while the grain length is comparable to the CDW coherence length.

Recent study of the electronic structure and properties of (TiZrNbCu)1-xNix (x≤0.25) amorphous high entropy alloys (a-HEA [1]) has been extended to x=0.5 in order to compare the behaviours of a- HEA and a conventional Ni-base metallic glasses (MG). All samples were ribbons about 20 μm thick and their fully amorphous state was verified by thermal analysis and X-ray diffraction (XRD). XRD patterns were also used in order to deduce the nearest neighbour distances and probable local atomic arrangements [1, 2]. Precise composition and the distribution of components were studied with a scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) attachment. Here we studied thermal parameters (the glass transition temperature Tg, the first crystallisation temperature Tx and the melting and liquidus temperatures Tm and Tl respectively), the low temperatures specific heat (LTSH [1]), the magnetic susceptibility χexp and the Young's modules E. Except for E which was measured both for as-cast and relaxed ribbons (after a short anneal close to Tg) all other properties were measured on as-cast samples only. The LTSH showed that the electronic density of states of the Fermi level N(EF) decreases with increasing x, whereas the Debye temperature ΘD increases with x [1]. This is similar to what observed in binary and ternary MGs [2, 3] of early transition metals (TE) with late transition metals and indicates that N(EF) is dominated with the d-electrons of TE . Like ΘD , E, Tx and Tl increased with increasing x indicating the enhanced inter- atomic bonding on addition of Ni (similar to that observed in binary TE-Ni MGs [2, 4]). However Tx and Tl tend to saturate for x≥0.25 which seems to support a change in local atomic arrangement around x=0.25 deduced from the analysis of XRD patterns. The usual parameters associated with glass forming ability (GFA) showed little variation with x, thus no real change in GFA when going from a-HEA to conventional MGs in the studied system. As expected [1], the rule of mixtures gave poor description for most properties of our alloys. 1. K. Biljaković et al, J. Alloys Compd. 695, 2661 (2017). 2. R. Ristić et al, J. Alloys Compd. 621, 136 (2015). 3. R. Ristić et al, Solid State Commun. 151, 1014 (2011). 4. R. Ristić , M. Stubičar, E. Babić, Phil. Mag. 87, 5629 (2007).

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 Tg 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 ibrational 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.

International audience; We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor (NbSe 4) 3 I by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a welldocumented 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 * ≈ 160 K. Although antiferroelectric (AFE) phase is partially formed at T C , 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.

Unlike many metallic glasses, CuHfTi system for some concentrations can form bulk metallic glass. In order to establish possible correlation between glass forming ability (GFA) and thermodynamic parameters we have measured heat capacity (Cp) for Cu55Hf45-xTix (x=0, 5, 10, ..., 45) system ranging from 1.8 K up to room temperature for as-cast and annealed samples. Cp of metallic glasses in general does not obey known phonon T3 law which predicts Debye model and one of the anomalies is a wide peak around 10 K which is known as boson peak (BP). Here, we present low-temperature Cp parameters and the intensity of the BP given as subtraction of the measured heat capacity and sum of the Debye phonon and electronic contribution as a function of x. The intensity of BP correlates well with GFA of studied CuHfTi alloys.

Electric conductivity of charge density wave (CDW) systems exhibits rich variety of behavior ; thermal activation across the gap at low fields below transition temperature TP, collective contribution (nonlinear conductivity channel) above the threshold field (ET) and variable range hopping (VRH) at low temperatures and in granulated thin films in the whole temperature range . Particularly the origin of the hopping conductivity is still unclear. We have investigated the influence of disorder on conductivity phenomena in CDW systems TaS3 and blue bronze (BB: K0.3MoO3) in a wide range of temperatures and electric fields using both the DC and pulse measurements at low and high fields respectively. Disorder has been introduced in several ways: (1) synthesis of TaS3 samples doped with Nb, (2) irradiation of nominally pure TaS3 samples and (3) deposition of granular thin BB films by pulsed laser deposition (PLD). Our results show that the nonlinear conductivity can be described by VRH already below 50 K in contrast to the linear channe, where it appears only below 20 K. Moreover, the point defects in TaS3 introduced by doping and irradiation have no effect on VRH. Together with the dielectric data, it suggests the microscopic picture of soliton hopping in CDW at low temperatures. In granular thin BB films, on the other hand, the influence of grain boundaries is overwhelming even above TP, which is in contrast to the previous experiments on thin BB films. The results can be understood by applying recent theoretical results for Beloborodov's Efros- Shlovskii VRH in granular materials.

Quasi‐one‐dimensional metal (q‐1D) K0.3MoO3, exhibits so‐called Peierls transition to a charge density wave (CDW) state with periodic charge density modulation and concomitant lattice distortion at a transition temperature Tp=180 K. Despite the fact that the physical properties of q‐1d bulk materials have been widely investigated, they can drastically change due to reduced dimensionality if the material is in the form of thin film. We present results of the production of K0.3MoO3 thin films by pulsed laser deposition (PLD). Standard characterization techniques showed that our films are composed of nano‐sized metallic grains and presence of CDW in grains was unambiguously proved by femto‐second time resolved spectroscopy (fs‐Trs). This technique also showed that the amplitude mode appears in films at a temperature that is some 30 K lower than in the crystal. Transport measurements in a wide temperature range indicated smeared Peierls transition in some films, at a temperature that is some 30 K lower than in bulk, which is in accordance with fs‐Trs. We have established a connection between film morphology and resistance, namely films with better ordering show lower resistance and more pronounced anomaly at 150 K. Furthermore, our films appear to be well fit by variable range hopping conductivity (VRH) in the almost entire temperature range, which is a characteristic of disordered materials.

U ovom radu je predstavljen utjecaj parametara proizvodnje (temperatura podloge Ts i parcijalni pritisak oksigena p02) na granularne tanke filmove K0.3MoO3 (kalijeva plava bronza) proizvedene pulsnom laserskom depozicijom (PLD). Filmovi su ispitani različitim standardnim tehnikama kao što su UV-vis spektroskopija, skenirajuća elektronska mikroskopija (SEM), rendgenska difrakcija (XRD), mikroskopija atomskim silama (AFM), femtosekundna- vremenski razlučiva spektroskopija (fs-TRs) i mjerenje električnog transporta. Općenito, K0.3MoO3 predstavlja prototip kvazi- jednodimenzionalnog (q-1D) materijala koji prelazi u kolektivno stanje vala gustoće naboja (VGN) na temperaturama nižim od temperature prelaza Tp. Njegova svojstva su dobro poznata i ispitana u kristalima, a zbog smanjene dimenzionalnosti, filmovi sa VGN stanjem omogućavaju proučavanje fizikalnih svojstava ovih sistema na mezo i mikro skalama. Amaliza eksperimentalnih rezultata pokazuje da su filmovi sastavljeni od nanokristalnih zrna čija veličina i orjentacija zavise od parametara proizvodnje. Mjerenja električnog transporta i fs- TRs su omogućila detekciju faznog prelaza u VGN osnovno stanje na temperaturi oko 30 K nižoj u filmu nego u kristalu.

We have investigated the low temperature heat capacity of Cu55Hf45‐xTix metallic glasses in the entire range of Ti concentrations, x=0‐45. We have established the most appropriate procedure for the analysis of data and for the estimate of low temperature electronic and phonon contributions. 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 (GFA) in the Ti concentration range x=15‐30. Our results indicate that the thermodynamic parameters (e.g. reduced glass temperature) remain the most assertive indicators of GFA for bulk metallic glasses. However, we discuss the possibility to correlate more subtle glass‐like contributions to the heat capacity, such as the Boson peak, with GFA.

The first thin-film growth of the “blue bronze”, oxide X0.3MoO3, well-known for its charge density wave (CDW) ground state, with X=Rb was realized a decade ago by pulsed laser deposition (PLD). However, the deposition of X=K blue bronze thin films was successfully realized only last year. The relevant parameters for successful PLD are the repetition rate, the fluence, the number of pulses, the distance between the target and the substrates, the substrate temperature and the oxygen pressure. Keeping all other parameters constant, we have varied the oxygen pressure between 0.01 mbar and 0.1 mbar and the substrate temperature between 375 °C and 450 °C with several attempts at 350 °C and 500 °C. Here we present the optimal conditions in p-T parameter space for the pulsed laser deposition of K0.3MoO3 films based on the characterization by several standard methods.

We present the temperature and magnetic field dependence of the heat capacity Cp of quasi one-dimensional system CuSeO3 and quasi two-dimensional system Fe8Te12O32Cl6. CuSeO3 [1] has an orthorhombic structure with linear Cu2+ chains very similar to CuGeO3 [2], a well known spinPeierls system [3]. We have observed a BCS-like transition at Tc=8.2 K with very similar features as in CuGeO3 [4], including the broad maximum in the magnetic contribution to Cp well above Tc [5]. However, the transition did not change even in the magnetic field of 8 T whereas in CuGeO3 both Tc and DCp at Tc decrease by 10% for in the same field [6]. Moreover, the magnetic susceptibility of CuSeO3 indicates AFM ordering and magnetic anisotropy even more complex diagram with probable tetramerization of Cu2+ spins along the chain. Fe8Te12O32Cl6 is a quasi two-dimensional system with the magnetically active Fe atoms arranged on the distorted honeycomb lattice within the layer [7]. Although Fe8Te12O32Cl6 is a good insulator, the low temperature Cp shows a strong linear contribution. However, this linear contribution ceases at the transition temperature Tc=30 K. The transition is rather small and wide, and the overall entropy change is only 3 J/mole K. Tc corresponds nicely with the narrow maximum in the magnetic susceptibility which does not resemble any standard transition. Both Tc and DCp at Tc decrease strongly with applied magnetic field and at 0.5 T it is hardly observable in the background of the lattice contribution. Magnetic susceptibility is similarly strongly dependent on applied magnetic field below 30 K, however at lower temperatures shows clearly the spin-flop transition characteristic for AFM order. We assign tentatively the results of Cp to the strongly fluctuating one-dimensional AFM order which sets in at 30 K and supports spin wave excitations below Tc. [1] K. Kohn et al., J. Solid State Chem. 18 (1976) 27 [2] H. Völlenkle et al., Monatsch. Chem. 98 (1967) 1352 [3] K. Uchinokura, J. Phys.: Condens. Matter 14 (2002) R195 [4] S. Sahling et al., Solid State Commun, 92 (1994) 423 [5] M. Weiden Z. Phys. B 98 (1995) 167 [6] G. Remenyi et al., J. Low Temp. Phys. 107 (1997) 243 [7] R. Becker, M. Johnsson, J. Solid State Chem. 180 (2007) 1750

Probing charge density wave system (CDW) o-TaS3 with dielectric spectroscopy reveals two processes determined by the CDW phase dynamics, one of which (-process) freezes at finite glass transition temperature TG at which there is less then one free carrier per phase coherence domain [1]. Irradiating the samples by 2 MeV protons we introduced interstitials and vacancies in the lattice, uniformly throughout the sample. We have observed gradual decrease of amplitude of the -process upon increasing the radiation dose, along with an increase of TG, while the other (-process) has been left unchanged. Increase of TG depends on the irradiation dose, and consequently on the domain size, in the activated manner (see Figure). It follows closely the temperature dependence of free carrier density, which does not change with the irradiation. Our results confirm previously suggested freezing criterion for CDW phase [1]. [1] D. Starešinić et. al. Phys. Rev. B 65 (2002) 165109.

Thin granular films of charge density wave (CDW) system K0.3MoO3 were prepared by pulsed laser deposition and investigated by various standard characterization methods such as GI-XRD, electric transport, TOF-ERDA, AFM and UV-vis spectroscopy. While all these methods indicate that the thin films consist of nanometer grains of K0.3MoO3, it is only the non-destructive femtosecond time-resolved spectroscopy (fsTRS) that demonstrates the charge density wave nature of the ground state and therefore proves directly the presence of K0.3MoO3. Furthermore, the comparison of the fsTRS data obtained in thin films and in single crystals shows the reduction of the charge density wave transition temperature and of the photoinduced signal strength in granular thin films in respect to single crystals, which is attributed to the granularity and crystal growth morphology. Our results establish fsTRS technique as the indispensible tool for the detection and characterization of complex ground states in nano-sized systems. Photoinduced reflectivity transients in a) bulk K0.3MoO3 and b) thin film of K0.3MoO3 on Al2O3 substrate as a function of temperature recorded at the same excitation density.

Charge density wave (CDW) is a spatial modulation of conducting electrons accompanied by the lattice modulation which appears in some quasi one-dimensional metallic crystals at low temperatures. Due to the strong polarizability at QCDW=2kF, kF being the Fermi wave vector, quasi one-dimensional electron gas screens and softens the phonons of corresponding wave length until a new periodicity sets in and the gap opens at the Fermi level. Near QCDW, electron and phonon degrees of freedom combine to give new spectrum of the excitations of the complex CDW order parameter: acoustic-like phase excitations (phasons) and optic-like amplitude excitations (amplitudons) [1]. We demonstrate that the heat capacity Cp in these systems is nevertheless very similar to Cp of ordinary glass formers such as a-SiO2. The heat capacity of CDW systems o-TaS3, K0.3MoO3, (TaSe4)2I, NbSe3 and K2Pt(CN)4Br0.3 x 3.2 H2O (KCP) is characterized by the power law contribution at lowest temperatures [2, 3] and the maximum in Cp/T3 in excess to the regular Debye heat capacity [3]. These features correspond very well to the power law contribution from low energy excitations and the Boson peak in glasses. We discuss the results in the light of the glass transition observed in the low frequency dielectric response of CDW systems [4]. The phase excitations which govern the low energy properties of CDW are strongly affected by the interaction with random impurities. Impurity pinning breaks CDW in the domains of correlated phase, opens the gap in the acoustic-like phason spectrum and leads to the resonant response in the 10-100 GHz frequency range [1]. Low frequency CDW dynamics freezes at temperatures where the number of free carriers excited across the CDW gap is not sufficient to screen the long range CDW deformations across the domain boundaries [4]. Below the glass transition the coherent phase excitations are confined to the domains of characteristic micron sizes which determines a sort of as Ioffe-Regel limit for phason propagation. The maximum in Cp/T3 in CDW systems can be well described by the acoustic dispersion with the low frequency cut-off corresponding to the pinning resonance frequency and consistent with the phase domain size [5]. [1] G. Grüner, Rev. Mod. Phys. 60 (1988) 1129 and references therein [2] K. Biljaković, Phys. Rev. Lett. 96 (2006) 039603 [3] K. Biljaković, et al., Physica B 404 (2009) 456 and references therein [4] D. Starešinić et al., Phys. Rev. B 65 (2002) 165109 ; ibid. 69 (2004) 113102 [5] K. Biljaković et al., Phys. Rev. Lett. 57 (1986) 1907 ; J. Odin et al., Eur. Phys. J. B 24 (2001) 315

Bulk magnetic measurements have revealed that magnetic units in SeCuO3 systems are tetramers, linear segments of 4 magnetic moments. Intra-tetramer correlations show around 200 K while the 3D ordering sets in at 8 K. Above 8 K one can expect a strong influence of quantum fluctuations.

The dynamics of charge density waves (CDW) is described by the temporal changes of the amplitude and the phase of the complex CDW order parameter. Phasons (phase excitations) are acoustic-like low energy degrees of freedom and therefore govern low-frequency CDW response. Dynamics of the CDW dielectric glass transition strongly resembles scenario of freezing in supercooled liquids [1]. The well known CDW pinning is characterized by the resonant response at GHz frequencies. Screening by free carriers is tightly bound with the deformation of CDW and its relaxational dynamics giving the criterium for freezing at Tg [1]. CDW glassy phenomenology is completed with low-energy excitations, the peak in heat capacity (Cp/T3), long-time energy relaxation and aging found at low-T [2]. Relevant degrees of freedom in this new class of glass concern CDW superstructure on characteristic scales given by the size of the phase coherence length (lϕ~μm). As the lattice distortion associated with the CDW can be thought of as being a “frozen” phonon, we discuss its possible manifestations in relation with the phenomenology of Boson peak in glasses as freezing of incomplete softening of superstructural mode near glass transition temperature. The Boson peak frequency in CDW glass phenomenology can be seen as Ioffe-Regel limit for phason propagation, consistent with the pinning resonance (gap in the phason dispersion). Very well understood aspects of the microscopic picture in CDW systems dealing with pinning, screening and phasons as relevant excitations of defective superstructure (on mesoscopic, μm scales) and the parallels we draw with glass forming systems as defective soft structures (on nm scales) [3] might be of mutual interest for both fields.

The family of glasses includes nowadays numerous systems which are often very different from the classical glassformers, i.e. supercooled liquids. Even such exotic systems as charge density wave (CDW) superstructures occurring in quasi one-dimensional metals exhibit phenomena typical for glasses [1-3] including freezing of the primary relaxation (α) process at a finite temperature Tg [1], occurrence of the secondary (β) relaxation process below Tg [1], “Boson peak”- like [2] and power-law contributions [3] to the heat capacity. Disorder in CDW glasses is introduced on the level of superstructure through the pinning of CDW to crystalline defects which break CDW in domains determined by the coherence of the complex order parameter phase. Domain interaction is controlled by the screening of residual free carriers excited over CDW gap. Increase of the relaxation time at low temperatures follows the activated increase of resistivity which plays the role of viscosity. The glass transition occurs at a temperature Tg at which there is less then one free carrier per domain and the screening is no longer effective [1]. We have varied domain sizes in CDW system o-TaS3 over two orders of magnitude by proton irradiation which created additional defects. Dielectric spectroscopy on irradiated samples shows decrease of the amplitude and the microscopic relaxation time of α process, while the activation energy increases beyond the activation energy of resistivity, demonstrating increased cooperativity of the domains. Corresponding increase of Tg depends on the irradiation dose, and consequently on the domain size, in the activated manner. It follows closely the temperature dependence of free carrier density, which does not change with the irradiation, thus corroborating the freezing criterion for CDW glass. We demonstrate that Tg is closely related to the domain size in CDW glasses. As the microscopic model of CDW dynamics is well-established, our results might contribute to the understanding of the glass phenomenology in general.

Here we report on detailed studies of the photoexcited carrier and collective mode dynamics in prototype quasi-1D charge density wave (CDW) systems K0:3MoO3 and Rb0:3MoO3 focusing on their low temperature and low excitation range. We show that the order parameter relaxation dynamics are inconsistent with the Rothwarf– Taylor model describing the relaxation of the coupled quasi-particle and high frequency phonon system in a system with a narrow gap in the density of states. Therefore we propose an alternative model that accounts for the photoexcited carrier relaxation phenomena commonly observed in CDW systems.

Val gustoće naboja je statička prostorna modulacija rešetke i elektronske gustoće nastala elektron-fonon interakcijom. Prva teorija koja predviđa pojavu vala gustoće naboja (VGN) potječe iz 1954 u članku H. Fröhlicha, u kojem on pokušava objasniti pojavu supravodljivosti anomalnim efektima u kvazi jednodimenzionalnim (q-1D) sustavima. Tek tri desetljeća nakon, prvi eksperimentalni rezultati su potvrdili postojanje VGN sustava. I danas su ovakvi sustavi još uvijek zanimljivi za istraživanje zbog bogatstva otkrivenih efekata. Među ostalim, u VGNu se zbog nasumičnog zapinjanja na nečistoćama javljaju metastabilna stanja koja dovode do pojave histereze u raznim fizikalnim svojstvima, od kojih je najkarakterističnija ona u temperaturnoj ovisnosti DC vodljivosti. Predstavit ću temperaturnu histerezu niskofrekventnog dielektričnog odziva i električne vodljivosti na niskim poljima, kao i histerezu nelinearne vodljivosti u električnom polju VGN sustava $o-TaS_{;3};$. Između VGN prijelaza na 220 K i staklastog prijelaza na 50 K i amplituda i vrijeme relaksacije niskofrekventnog relaksacijskog procesa su viši u grijanju nego u hlađenju sa sličnim temperaturnim ovisnostima kao i histereza otpornosti na niskim poljima. Naši rezultati sugeriraju da je histereza u dielektričnom odzivu povezana sa histerezom u DC otpornosti putem zasjenjenja VGN faze slobodnim nosiocima. U nelinearnoj vodljivosti postoji samo histereza u polju i to samo u prvom ciklusu polja, nakon dovoljne promjene u temperaturi, kada se postepenim povećanjem polja sustav dovodi kroz niz metastabilna stanja. Ovaj efekt se odnosi na unutarnje opuštanje VGN-a koje prethodi klizanju VGN-a.

We present the effects of the isoelectronic supstitution of Ta by (0.2 and 0.5 %) Nb atoms on the charge density wave (CDW) properties in o-TaS3. The characteristic, primary relaxation process which gives the maximum in the dielectric constant near 100 K disappears with slight doping. At the same time the minimum in threshold field in the same temperature range disappears as well, which is expected from well known relation between ET and low frequency dielectric constant [1]. This implies that the primary process it mainly due to polarization on order of domain scale, which decreases by doping. The secondary process, on the other hand, as well as low energy excitation contribution to specific heat (CLEE), seem to be unchanged. Only the amplitudes of the two are increased [1, 2], as both are due to the local excitations of the CDW phase in vicinity of defects described by two level system (TLS) model. [1] Staresinic et. al, Phys. Rev. B, 65, 165109 (2002) [2] Biljakovic et. al, Europhys. Lett., 62 (4), pp. 554--560 (2003)

Niz kvazi jednodimenizonalnih lančastih vodiča baziranih na TMTSF molekuli prelazi na niskim temperaturama u stanje vala gustoće spina (VGS) koje odgovara nesumjerljivom anitferomagnetskom stanju. S druge strane, snižavanjem temperature ispod VGS prijelaza dielektrični odziv pokazuje porast dielektrične konstante praćen usporavanjem niskofrekventnog procesa opuštanja koje dovodi do prijelaza u stanje VGS stakla. Takvo ponašanje karakteristično je za takozvane relaxor feroelektrike. Supostojanje magnetskog i nabojnog ured¯enja ukazuje na multiferoicˇnu prirodu VGSa i otvara moguc´nost da su magnetska i dielektricˇna svojstva med¯uovisna. Naša mjerenja niskofrekventnog dielektričnog odziva dvaju VGS sistema, (TMTSF)2AsF6 i (TMTSF)2PF6, u magnetskom polju do 8 T pokazuju jaku povezanost magnetskih i nabojnih stupnjeva slobode. Povećavanjem magnetskog polja u smjeru tvrde osi VGSa dielektrična konstanta i vrijeme opuštanja povećaju se do za red veličine, naročito u okolici temperature prijelaza u staklo od oko 2 K. Taj takozvani magnetokapacitivni efekt izraženiji je od otprije poznatog magnetootpornog efekta. Zbog toga se ne može objasniti samo promjenom zasjenjenja slobodnim nosiocima naboja, već se mora uzeti u obzir i direktan utjecaj magnetskog polja na stanje VGSa, na primjer kroz povećanje elastičnosti ("mekšanje") VGSa ili kroz smanjenje jakosti zapinjanja.

The wild fires of the vegetation are in the Mediterranean countries very frequent, the fire fighting requires extensive resources, material losses are significant and casualties of firefighters are one of the worst consequences. Due to large spatial extension, and the duration of several days, many of the vegetation wild fires are often demanding for advancement of the firefighting technology. In Croatia is the existing organization a mixture of the public professional firefighting brigades and firefighter volunteers and it can successfully cope with smaller and medium vegetation wild fires. In the case of the dynamic spreading of the fires at larger area and lasting more than day or two, these resources are not sufficient. There are several approaches how to improve efficiency of the available fire fighting resources and they are related to costly organizational changes, change of funding scheme, purchasing the new technology etc. Nevertheless, to the future of the started processes, the training of the fire fighting commanding officers and operations managers is a constant need and it is part of the normal activity. One part of the education and training not implemented yet is the training for management and commanding in larger and spatially and temporally changing fires of the vegetation, requiring more firefighters (e.g. more than 100). The vegetation fires in the year 2007. In the coastal region, especially in the Dubrovnik – Neretva County, show all deficiencies of the existing fire fighting system in the Republic of Croatia and stress the need for urgent and significant advancements.

30 years ago, in his paper on the interplay between the commensurability pinning and impurity pinning in 1D CDW (charge density wave), H. J. Fukuyama predicted that CDW-CDG (charge density glass) transition should be also expected as a function of the temperature [1]. We brought the experimental evidences that the real glass transition into the CDG phase occurs at a finite temperature and moreover that it is the generic feature of DW systems [2]. As pinning and screening are responsible for the glassy behaviour, CDG has a very special position in the field of glasses and it can be used as a playground for the investigation of the real nature of the glass transition, one of remaining enigmas in solid state physics. The dynamics of the CDW-CDG dielectric glass transition strongly resembles the scenario of the freezing in supercooled liquids (SCL) [2], however relevant degrees of freedom concern the CDW superstructure on characteristic scales of the size of the phase coherence length. These scales are of the order of microns, compared to few nanometers of SCL short–range order. It is shown that the glass transition temperature into CDG depends on the size of the phase coherent domains [3]. The glassy phenomenology is completed with low-energy excitations (LEE), long-time energy relaxation and aging found at low-T and a peak in heat capacity (Cp/T3). This peak resembles the boson peak (BP) in glasses and we show that pinning resonance can be assumed as a BP equivalent. Finally, one more peculiarity of CDG: LEEs of this new glassy state demonstrate very rich and unexpected magnetic properties [4]. [1] Fukuyama, H. J. Phys. Soc. Jpn 45, 1474 (1978) [ [2] Starešinić, D. et al. Phys. Rev. B 65, 165109 (2002) ; ibid, Phys. Rev. B 69, 113102 (2004) [3] Dominko, D. et al. this conference [4] Starešinić, D. et al. and Remenyi, G. et al. this conference

We have used the vegetation fire growth simulation software Farsite to simulate the spatio-temporal evolution of two historical vegetation fires that occurred on the Adriatic islands of Korčula in 1998 and Lastovo in 2003. The spatial, vegetation, meteorological and agrometerological data have been obtained from various national agencies. The historical fire perimeters have been collected by firefighting commanders. By selecting the appropriate fuel models from the extended set of fuel models in Farsite, we have obtained a very good match between the simulated fire perimeters and observed ones. The sets of fire models corresponding to the Mediterranean vegetation on these two islands will be used as the starting point for the calibration of Farsite for the operational use in the Croatian firefighting organization.

In charge density wave (CDW) systems the interaction of CDW superstructure with the random defects introduces the localized low energy states which are responsible for various glass-like phenomena. In particular, the cooperative dynamics of phase coherent domains leads to the glass transition [1] on the level of the CDW superstructure. The domain size, which depends on the amount of disorder, is supposed to play an important role in determination of the glass transition. In order to test this assumption we have investigated the dielectric response and the nonlinear conductivity of a number of o-TaS3 samples irradiated with protons in a wide range of irradiation doses. Our results demonstrate that the increase of disorder with irradiation leads to the strong decrease of the low frequency dielectric response corresponding to the high temperature relaxation process ( process of [1]), but does not affect substantially the low temperature, or  process. Moreover, the relaxation time of  process increases faster at low temperatures, indicating the increase of the glass transition temperature. At sufficiently high irradiation doses  process in not detectable any more, consistent with prior results for Nb doped samples [2]. The threshold field ET, on the other hand, increases with irradiation. This increase is non-uniform and it is the most pronounced in the temperature region where the  process dominates. This leads to the quantitative changes in the temperature dependence of ET, where a characteristic minimum disappears at high irradiation doses. Nevertheless, the inverse proportionality of ET and the dielectric constant still remains. [1] D. Starešinić, K. Biljaković, W. Brütting, K. Hosseini, P. Monceau, H. Berger, F. Levy, Phys. Rev. B 65, 165109 (2002) [2] D. Starešinić, K. Biljaković, P. Lunkenheimer, A. Loidl, J. C. Lasjaunias, J. Phys. IV France 131, 191 (2005)

Multiferroics, materials with coupled different types of order, such as electric, magnetic and structural, have raised a lot of interest recently due to the multiple application possibilities. Spin density wave (SDW) systems with their incommensurate antiferromagnetic order [1] and relaxor ferroelectric-like dielectric response [2] seem natural candidates to exhibit such phenomena, as some early results indicate [3]. We have measured the low frequency dielectric response of CDW system (TMTSF)2AsF6 at very low temperatures down to 1.9 K in the magnetic fields up to 8 T. The influence of the magnetic field on the dielectric properties is negligible with the field in the direction of the easy axis b’, while it is important with the field in the direction of the hard axis c*. This effect is the most pronounced at the lowest temperature. As expected [4], at 1.9 K the resistivity increases up to 4 times almost linearly with the field. However, both the amplitude and the relaxation time of the low frequency relaxation process [2] increase for at least an order of magnitude. As such increase cannot be explained by free carrier screening only, we conclude that the magnetic field has to influence the SDW state directly as well. In addition, our results indicate the existence of the phase transition at 2.1 K [3], and the increase of the SDW glass transition temperature [5] with the magnetic field. [1] W.M. Walsh et al., Phys. Rev. Lett. 45, 829 (1980) ; J.C. Scott et al., ibid. 45, 2125 (1980) [2] F. Nad’, P. Monceau, K. Bechgaard, Solid State Commun. 95, 655 (1995) [3] J. L. Musfeldt, M. Poirier, P. Batail, C. Lenoir, Phys. Rev. B 52, 15983 (1995) [4] P. M. Chaikin, P. Haen, E. M. Engler, R. L. Greene, Phys. Rev. B 24, 7155 (1981) [5] J. C. Lasjaunias, et al, Phys. Rev. Lett. 72, 1283 (1994)

We report on broadband dielectric spectroscopy on the one-dimensional semiconductor (NbSe4)3I. Below the structural phase transition close to 270 K, which is accompanied by complex charge-order processes, we observe colossal dielectric constants with a frequency and temperature dependence very similar to what is observed in charge-density wave systems.

We report on very precise measurement of thermopower and resistivity of K-and Rb- blue bronze, K0.3MnO3 and Rb0.3MnO3. We have found that, as in K0.3MnO3, there exists a deep low temperature minimum in the thermopower of Rb0.3MnO3. There are some indications that it is due to phonon drag. However, it is interesting that the low temperature behaviour of the thermopower can be correlated to the resistivity. This correlation can explain why the thermopower does not follow simple 1/T behaviour above the minimum. Owning to our precise measurements, we are able to determine the temperature of the phase transition, TP, by the thermopower as well as by the resistivity data. The extracted values give that TP is 177.5 K for K0.3MnO3 177.8 K for Rb0.3MnO3, i.e. the same value within the errors of the measurements.

We report on new method of measuring sample length, based on interferometric measurements. Motivation for exploring this technique is to study the coupling between charge density wave (CDW) and underlying crystal lattice. Several papers report the dilatation measurements on CDW systems which can be related to CDW transition [1], CDW hysteresis [2], as well as low Temperature glass transition [3]. Coupling with lattice is also evident from calorimetric measurements at glass transition temperature [4]. Our aim is to apply this method to other CDW systems as well as other systems with electronic superstructure.

Charge density wave (CDW) ground state consists of coherent superposition of bound electron-hole pairs from opposite sides of quasi one-dimensional (q1d) Fermi surface with 2kF common wavevector. The properties of new state at sufficiently low excitation energies can be described by spatio-temporal variations of corresponding order parameter. As CDW has zero net spin, majority of CDW models does not discriminate between different spin channels and, moreover, consider only the low lying excitations of CDW phase (phasons).

The quasi-onedimensional (Q1D) systems with charge density wave (CDW) ground state have been extensively investigated in the eighties until a “ concensus” on their properties has been reached, or maybe until the high temperature superconductors have been discovered. However, even 20 years later these systems do not end to surprise us that have continued the efforts to study them. Glass transition in the superstructure, random exchange Heisenberg antiferromegnetic chain (REHAC) behaviour of the susceptility, extreme doping sensitivity of the dielectric response and heat capacity, large thermal hysteresis in the dielectric response, large sensitivity of the low temperature conductivity on electric excitations which I will present are only some of many interesting phenomena that we have recently observed.

We show that the low temperature (T

We present the effects of doping on the relaxational dynamics and the specific heat (Cp) of the charge density wave (CDW) system o-TaS3. Isoelectronic substitution of Ta atoms with 0.2% of Nb suppresses the primary relaxation process responsible for the glass-like dielectric response of pure o-TaS3 [1], but affects only slightly the secondary process as well as the low energy excitation (LEE) contribution to Cp. As it is well established that doping destroys the long range CDW order, our results show that the primary relaxation process is mainly due to long range deformations of the CDW, which are prevented by doping, while the secondary process and the LEE contribution to Cp originate from local topological defects of the CDW still present in doped samples.

We have measured the dielectric response of charge density wave (CDW) system o-TaS3 on both cooling and heating through the glass transition temperature Tg [1]. I addition to the well-known thermal hysteresis in the DC conductivity, we have observed a pronounced hysteresis in the amplitude and in the characteristic relaxation time of the dielectric response above Tg. Both the amplitude and the relaxation time are higher on heating away from than on cooling towards Tg, indicating that the CDW system finds itself in a more corrugated phase space after freezing.

Low frequency relaxation dynamics of charge density wave (CDW) superstructure in several quasi one-dimensional systems bears striking resemblance with canonical glass forming systems. Wide temperature and frequency range dielectric spectroscopy of semiconducting CDW systems o-TaS3 and K0.3MoO3 demonstrates the splitting of the relaxation spectrum in two processes, slower alpha and faster beta, on decreasing the temperature and subsequent freezing of alpha process at finite, glass transition temperature Tg. Maximum observed in thermally stimulated discharge current at Tg corroborates the freezing of alpha process. Our results are explained in the model of cooperatively relaxing CDW domains of coherent phase coupled through electrostatic interaction. At lower temperatures, in the absence of free carrier screening, this leads to the freezing of the elastic degrees of freedom, i.e. alpha process. The remaining beta process represents the dynamics of topological defects developed on the domain boundaries. We draw the parallels between this microscopic model and the phenomenological model of supercooled liquids, bearing in mind micrometer-size characteristic length scales of CDW domain.