S. Bernik

Jožef Stefan Institute | IJS · Department of Nanostructured Materials

Single crystal ingot of BiSbTeSe doped with Zr was synthesized using Bridgman method. Energy dispersive spectrometry (EDS) analysis was used to determine chemical composition of studied samples as well as to check and confirm samples homogeneity. X-ray diffraction (XRD) measurements proved that obtained crystal ingot is a single cristal and confirm...

High abundance and low toxicity make zinc oxide very attractive for broad application in the field of photocatalysis for remediation of toxic compounds from water. Its performance could be elegantly improved by inducing native defects into ZnO semiconductor nanocrystals. However, this typically requires post-processing at high temperatures, during...

This paper presents an innovative approach to the integration of thermoelectric microgenerators (μTEGs) based on thick-film thermopiles of planar constantan–silver (CuNi-Ag) and calcium cobaltite oxide–silver (Ca3Co4O9-Ag) thick-film thermopiles with radio frequency identification (RFID) technology. The goal was to consider using the TEG for an act...

As part of research on the influence of selenium as dopant on bismuth telluride, a successful synthesis of single crystal was carried out. Single crystal of p type conductivity, with the given compound formula, Bi2Te2.88Se0.12, was obtained by the Bridgman process. The obtained empirical formula does not deviate from the given compound formula. Sin...

Sintering in a reducing atmosphere, in comparison with sintering in air, greatly improves the electrical performance of ZnO-based thermoelectric materials. However, it also raises a question concerning their chemical stability in air for applications at high temperatures. The influence of annealing in air at temperatures up to 1000°C on the charact...

Novel ZnO-Cr2O3-based varistors can overcome the problems related to the volatile, high-cost and toxic components of conventional ZnO-Bi2O3-, ZnO-Pr6O11-, and ZnO-V2O5-based varistors. The influence of the varistor former with different doping levels, i.e., the Cr2O3, on the microstructure and electrical properties was examined and the optimal amou...

Polycrystalline samples of NaCo2−xCuxO4 (x = 0, 0.01, 0.03, 0.05) were obtained from powder precursors synthesized by a mechanochemically assisted solid-state reaction method (MASSR) and a citric acid complex method (CAC). Ceramic samples were prepared by pressing into disc-shaped pellets and subsequently sintering at 880 °C in an argon atmosphere....

The influence of Ca-doping on the microstructure development and electrical characteristics was studied in the novel, ZnO-Cr2O3-based, varistor ceramics with the nominal composition (99.47-x) mol% ZnO + 0.1 mol% Cr2O3 + 0.33 mol% Co3O4 + 0.1 mol% La2O3 + x mol% CaCO3, with x ranging from 0 to 6, sintered at 1200 °C. The results showed that, within...

The nonlinear response of a material to an external stimulus is vital in fundamental science and technical applications. The power-law current–voltage relationship of a varistor is one such example. An excellent example of such behavior is the power-law current–voltage relationship exhibited by Bi2O3-doped ZnO varistor ceramics, which are the corne...

SADRŽAJ – CONTENT Scientific papers Slavko Bernik, Matejka Podlogar, Nina Daneu, Aleksander Rečnik A novel approach to tailoring the microstructure and electrical characteristics of ZnO-based varistor ceramics via inversion-boundary (IB) induced grain growth ..............73 S. Nineva, TS. Dobrovolska, I. Krastev Electrodeposition of Sb-In, Sb-Co a...

SADRŽAJ – CONTENT Miodrag V. Zdujić, Slobodan D. Petrović, Nataša V. Valentić, Dušan Ž. Mijin On the synthesis of 3-cyano-6-hydroxy-4-methyl-2-pyridone at room temperature ................................................................... 229 Dragana V. Medić, Slađana Č. Alagić, Snežana S. Milić Toksičnost osnovnih komponenti u Li-jonskim baterija...

The chapter presents the main research activities and the progress made in polycrystalline oxide thermoelectric materials over the past decade. It starts with a general presentation of oxide thermoelectric materials and their characteristics to bring forward the main challenges for the enhancement of their thermoelectric performance. In the main pa...

n-type ZnO-based semiconducting materials are increasingly studied for thermoelectrics (TE) in the past due to their inexpensive and non-toxic nature coupled with their high Seebeck coefficient and stability at elevated temperatures. However, their high thermal conductivity limits their prospect for TE application. In this work, a novel, simpler an...

Antimony doped barium-stannate dense ceramic materials were synthesized using spark plasma sintering technique out of mechanically activated precursor powders. The influence of various Sb concentrations (x = 0.00 – 0.10) on properties of BaSn1-xSbxO3 ceramics was investigated. Relative densities of prepared samples were in the range of (79 – 96) %....

Following the 3 Sn(IV)S˟n (IV) ⇋ Co(II)Sn ̎(IV) + 2 Ta(V)˙Sn (IV) charge compensation mechanism we optimized densification and electrical properties of Ta2O5-doped SnO2–CoO ceramics. We show that incorporation of acceptor dopant Co²⁺ in SnO2 is promoted after the addition of donor dopant like Ta⁵⁺, whereas any surplus of Co would form secondary Co2...

We investigated the effect of pentavalent donor dopant Ta2O5 on microstructure development, electric and dielectric characteristics of SnO2–CoO based ceramics. Already low additions of Ta2O5 (0.05 mol%) effectively reduce the porosity, improve densification and dielectric permittivity and trigger a 3–fold increase in SnO2 growth rate. Rietveld anal...

We investigated the effects of dual doping of SnO2 varistor ceramics with 1 mol% CoO and different amounts of Nb2O5 (0.1 - 2 mol%) on the formation of twin boundaries, microstructure development and electrical properties. Nb2O5 addition shifts densification to higher temperatures (up to 1430 °C), producing microstructures composed of twinned SnO2 g...

ZnO-Bi₂O₃-based varistor ceramics are typically sintered at temperatures above 1100 °C to ensure the proper microstructure development and the required current-voltage (I-U) characteristics. In this investigation the influence of the sintering regime at temperatures between 800 and 950 °C on the microstructure development and the I-U characteristic...

El lingote del mono cristal de BiSbTeSe dopado con Zr se sintetizó utilizando el método de Bridgman. La composición química se determinó mediante análisis con espectroscopía de dispersión de energía (EDS). Mediante difracción de rayos X (DRX) se demostró que el lingote de cristal obtenido es un mono cristal y confirmó que se trata de un compuesto d...

Granulates G1, G2 and G3, having the same varistor composition but different morphologies in terms of shape, size and size distribution, were characterized for their compactness and flow characteristics. They were also examined during the preparation of disc-shaped green pieces with a diameter of 20 mm by uniaxial pressing at pressures from 3.2MPa...

Both the spark plasma sintering (SPS) method and reducing atmosphere sintering (N2 + CO) method could greatly improve the electrical performance of ZnO-based thermoelectric materials. However, there is no comparison of these two methods which is essential for further improvements to the thermoelectric performance. In this article, a systematic comp...

In this work, we investigated the influence of Al doping on the structure of the (ZnO)5In2O3 homologous phase and the thermoelectric characteristics of (ZnO)5(In1−xAlx)2O3 ceramics for x=0, 0.01, 0.03, 0.05, 0.1, and 0.2, prepared using a classic ceramic procedure and sintering at 1500°C for 2 hours. The Al substituted for In on both the primary si...

The (ZnO)kIn2O3 system is interesting for applications in the fields of thermoelectrics and opto-electronics. In this study we resolve the complex homologous phase evolution with increasing temperature in polycrystalline ceramics for k = 5, 11 and 18 and its influence on the microstructural development and thermoelectric properties. The phase forma...

Nearly stoichiometric Ti1.005S2 was prepared by a solid-state synthesis of the constituent elements and consolidated under a variety of processing conditions applied using pulsed-electric-current sintering. The non-stoichiometry in the Ti1 + xS2 induced during the sintering was quantitatively determined with a Rietveld structural refinement and a t...

ZnO is a promising thermoelectric material for high-temperature applications; however, the strong correlation between the electrical and thermal transport properties has limited their simultaneous optimization to achieve superior thermoelectric performance. In this work, defect engineering was applied to solve this problem. The results revealed tha...

The drying of microcapsules causes agglomeration and oversized agglomerates disturb fiber melt spinning. In this study, three parameters in co-current spray drying were studied and their influence on agglomeration was established with a morphological analysis, granulometric analysis, differential scanning calorimetry (DSC), and thermal gravimetric...

Understanding growth mechanisms usually leads to the successful preparation of a targeted microstructure. However, the large number of parameters that influence the shape and the size of nanostructures often make it difficult to predict the outcome. We investigated the growth of wurtzite-type ZnO by closely following such a multistage process. We a...

WO3-doped ceramics with the composition Ca3Co4−xWxO9 and x=0, 0.02, 0.05 0.1 and 0.2 were prepared by the classic ceramic procedure from fine oxide powders and sintering in air at 900 °C. The influence of the composition on the microstructure development and the thermoelectric characteristics in the temperature range from 40 °C to 615 °C was studie...

Single-phase Ca3Co4O9 with a high porosity, having a ZT of 0.09 at 627 °C, was successfully prepared by a simple solid-state reaction using fine powders of CaCO3 and Co3O4 after a calcination at 760 °C for 12 hours. It was excellent either for the preparation of the starting powder for the processing of the Ca3Co4O9 ceramics or for direct processin...

An alternative to the expensive and time-consuming processing of the bulk thermoelectric microgenerators (TEG) could be the structuring of TEG by means of screen-printing technology. An oxide-based semiconducting TEG could have many advantages, such as non-toxicity, thermal stability and oxidation resistance at high temperatures. Two types of therm...

The preparation of screen-printing inks with a high solids load was studied for the development of thick-film varistors. A high solids load can ensure a higher green density of the films for enhanced densification and microstructure development in order, to obtain good current–voltage (I–U) characteristics for the thick-film varistor, even after sh...

The phase evolution, microstructure, and electrical properties of WO3-doped ZnO–Bi2O3-based varistors were investigated for different amounts x (0 ≤ x ≤ 1.60 mol%) of the dopant. When x was less than 0.40, the dissolved W6+ in the β-Bi2O3 acted as a donor in the grain boundaries and reduced the electrical properties of the ZnO varistors. However, w...

Copper zinc tin sulfide (Cu2ZnSnS4) has been receiving a lot of attention in recent years as a new, alternative absorber for the production of cheap thin film solar cells owing to the high natural abundance of all the constituents, its tunable direct-band-gap energy, and its large optical absorption coefficient. In addition, to overcome the problem...

As a promising and alternative solar absorber material, the copper–zinc–tin–sulfide compound (Cu2ZnSnS4) has been drawing attention in recent years for the production of cheap thin-film solar cells owing to the high natural abundance and non-toxicity of all the constituents, a tunable direct-band-gap energy and a large optical absorption coefficien...

Microstructure development in ZnO ceramics with Bi4Ti3O12 (BIT) additions was studied in dependence of sintering temperature, inversion boundary (IBs) nucleation, heating rate and doping with transition metal oxides (NiO, MnO2 and Co3O4). We demonstrated that one of the essential conditions for homogeneous microstructure development in this system...

Applications involving transparent conducting films (TCFs), such as flat-panel displays and touch screens technologies, are dominated by indium-tin-oxide (ITO). Increasing prices of indium in hand with weaknesses of ITO films make a strong argument for alternative TCFs with competitive characteristics and lower price. Here we demonstrate the potent...

Single-phase YMnO3, a multiferroic material, is synthesized for the first time by milling a mixture of Y2O3 and Mn2O3 in a planetary ball mill for 60—720 min.

Flat panel display technology seems to be an ever-expanding field developing into a multibillion dollar market. A set of technical solutions involve a transparent conducting film (TCF) that is today still dominated by indium-tin-oxide (ITO). In a race to find alternatives that would avoid the indium pitfalls, mainly due to its increasing price and...

Zinc oxide powders with different morphologies and grain sizes were synthesized using solvothermal methods from ethanolic zinc acetate solutions in the presence of lithium hydroxide. The influence of the temperature and the time of the reaction, as well as the pH value of the starting solution, on the ZnO particle size and morphology were examined....

The synthesis of the Ca3Co4O9 compound from starting powders of CaCO3 and Co3O4 by mechanochemical alloying was studied. This mechanochemical treatment resulted only in an amorphisation of the powder mixture without any phase formation or an enhancement of its formation. The Ca3Co4O9 phase formed in samples from untrteated and treated powder mixtur...

Lanthanum nickelate (LNO) is a perovskite oxide material with metallic conductivity in a wide temperature range which makes it suitable for application as electrode material for thin films. In this paper LNO thin films were prepared by polymerizable complex method from the diluted citrate solutions. Precursor solutions were spin coated onto Si-subs...

In ceramic materials, special boundaries play the key role in crystal growth. They introduce an abrupt structural and chemical anisotropy, which is readily reflected in an unusual microstructure evolution, whereas their local structure affects the physical properties of polycrystalline materials. These effects, however, can be exploited to tailor t...

In semiconducting materials special boundaries play the key role in crystal growth. They introduce an abrupt structural and chemical anisotropy, which is readily reflected in an unusual microstructure evolution, whereas their local structure affects the physical properties of semiconducting materials. These effects, however, can be exploited to tai...

Zinc oxide nanopowders were synthesized by the sol–gel method from an ethanol solution of zinc acetate dihydrate. Detailed structural and microstructural investigations were carried out using x-ray diffraction, Raman spectroscopy, thermogravimetric and differential thermal analyses, as well as high-resolution transmission electron microscopy (TEM)...

We have studied the formation of BiMnO3 (BMO) nanocrystalline perovskite powder produced by high-energy milling of the constituent oxides. The crystal structure and the amount of crystalline and amorphous phases in the powder as a function of the milling time were determined with XRPD using Rietveld refinement. BMO perovskite formed directly from h...

A novel immersion process was carried out to improve the electrical stability of ZnO varistors under a dc electrical field. It was performed by dipping the conventionally sintered ZnO varistor samples in a bismuth nitrate solution with a subsequent heat treatment. The results showed that this process could improve the electrical stability and the n...

ZnO grain-growth kinetics was studied in the ZnO+1 mol% Bi2O3 system with the addition of 0.1 and 0.5 mol% SnO2 between 950° and 1300°C. It was found that inversion boundaries (IBs) are the major factor influencing the ZnO grain growth in this system. After the nucleation of the IBs in the ZnO grains, these grains grow exaggeratedly and anisotropic...

The dc electrical stability of ZnO varistors was effectively improved by controlling the composition proportion of Bi2O3 and SiO2 as well as annealing condition. The microstructure, current–voltage (I–V) property, and dc degradation characteristics are significantly affected by the molar ratio of Bi2O3 to SiO2 in composition. It is found that a pha...

A novel approach to tailoring the microstructure and electrical characteristics of ZnO-based varistor ceramics via inversion-boundary (IB) induced grain growth ZnO-based varistors with exceptional current-voltage (I-U) nonlinearity are widely used in the over-voltage protection of electrical equipment and devices at voltages ranging from a few volt...

Raman scattering spectroscopy has been used for the characterization of zinc oxide nanoparticles obtained by mechanical activation in a high-energy vibro-mill and planetary ball mill. Raman modes observed in spectra of nonactivated sample are assigned to Raman spectra of the ZnO monocrystal, while the spectra of mechanically activated samples point...

Substituted lanthanum manganites with the general formula A1−x B x MnO3 (A = La, B = Ca, Sr…) have attracted a lot of attention due to their exceptional electric and magnetic properties. In this work, pure and Ca2+, Sr2+-doped LaMnO3 (LMO) with the concentrations of dopants 30% Ca2+ (LCMO), 30% Sr2+ (LSMO) and 15% Ca2+ + 15% Sr2+ (LCSMO) (in mol. %...

The relationship between microstructure texturing and electrical characteristics of a ZnO-based varistor system was investigated in comparison with a varistor system having the same chemical composition but conventional microstructure. Highly textured ZnO-based varistors were produced via the templated grain growth (TGG) technique. Stereological an...

The Mo–Ni–O powders were electrodeposited from ammonium sulfate containing electrolytes with dif-ferent Mo/Ni ion concentration ratios. The phase composition of these powders was investigated using TEM, EDS and XRD analysis. The TEM analysis showed that two types of particles were present in the pow-ders: amorphous and crystalline. For crystalline...

Multiferroic bismuth manganite (BiMnO3) is known as a material that exhibits both ferromagnetic and ferroelectric properties making it interesting for various technological applications. Unfortunately, preparation of BiMnO3 is not possible by a conventional solid-state reaction and it can form only from mixture of oxides at high pressures (>40kbar)...

In this paper, changes of microstructural characteristics of disperse systems during mechanical activation of zinc oxide (ZnO) have been investigated. ZnO powder was activated by grinding in a planetary ball mill in a continuous regime in air during 300 min at the basic disc rotation speed of 320 rpm and rotation speed of bowls of 400 rpm but with...

ZnO-based varistor samples were prepared by the direct mixing of the constituent phases (DMCP) and sintering at 1100 °C for 2 h. The influence of the starting powder mixture's composition – the amounts of the pre-reacted varistor compounds and their composition – and its preparation, either with or without mechano-chemical activation (MCA), on the...

The purpose of this research was to obtain porous, high-quality cathodes for solid oxide fuel cells in both planar and tubular shapes. To accomplish this, cathodic electrophoretic deposition of the LaMnO3 powder (synthesized by the modified sol–gel method proposed by Pechini) was performed. The optimal sintering temperatures were 1200°C and 1300°C...

In polycrystalline materials - both metals and ceramics - understanding and controlling the microstructure is very important since vital physical properties, critical for applications, are strongly influenced by the average grain size, the grain size distribution and the porosity. The influence of the microstructure is very straightforward in the c...

Two ways of application of intensive milling in ZnO varistors processing were compared. First was intensive milling of mixture of previously prepared constituent phases. In this case, intensive milling was applied only to obtain highly activated nanocrystalline varistor powder mixtures. Second application is intensive milling of simple mixture of o...

The aim of this work was to reduce number of additives using new method of preparation, refered as "direct mixing of the constituent phases". The method is based on sintering of a mixture of constituent phases with the following compositions: ZnO phase uniformly doped with 0.1 mol% Mn2+ and 0.1 mol% Co2+, gamma-Bi2O3 stabilized with Mn2+ and spinel...

The influence of Al2O3 doping in the range 0.00–0.83mol% on the microstructure and current–voltage characteristics of ZnO-based varistor ceramics sintered at 1200°C for 2h was studied. The threshold voltage VT (V/mm) increased up to a dopant level of about 0.08mol% Al2O3; the nonlinear coefficient α was significantly increased by additions of up to...

Grain growth studies of zinc oxide ceramics have indicated that inversion boundaries (IBs) are growth faults that control the growth of the zinc oxide (ZnO) grains. To substantiate this observation, we designed experiments to study the nucleation of IBs. Low-temperature experiments showed that in the ZnO–SnO2 system, IBs form before the Zn2SnO4 spi...

Grain growth in ZnO ceramics doped with 0.01 and 0.02 mol.% Bi2O3 and Sb2O3 in amounts appropriate for Sb2O3/Bi2O3 ratios of 0.8, 1.0 and 1.2, sintered at 1200oC for 2 and 10 hours, was investigated. Grain growth is promoted by a sufficient amount of the Bi2O3 liquid phase at the grain boundaries and also by the presence of IBs in the ZnO grains. W...

The grain growth of ZnO ceramics sintered with low additions of Sb2O3 (2O3 addition (45 m). The addition of 500 ppm of Sb resulted in a fine-grained microstructure with an average ZnO grain size of about 12 m. The results are explained by an inversion-boundary (IB) -induced grain-growth mechanism. The grain-growth exponent has a value of about 2...

In this work pure and doped LMO were prepared using modified Pechini method from lanthanum and manganese citrates. Lanthanum citrate was prepared starting from La2O3, while manganese citrate was prepared from Mn(NO3)2. Valence state of the manganese was controlled by adjusting pH value of the solution and confirmed by EPR and UV/VIS analysis. Therm...

Because of their unusual properties - non-ohmic behavior and the ability to absorb a lot of energy - metal-oxide varistors are widely used for the protection of electrical and electronic devices against over-voltages. ZnO ceramics have varistor properties because of their metal-oxide additives and the microstructures developed during sintering. The...

Ba-Sr-Ca-Cu-O (BSCCO) high Tc superconductor specimens were prepared as part of a solid-solubility study in the region of the 2223 phase. The identification and determination of the amount of each phase in the final products were necessary. Quantitative digital x-ray compositional mapping with the electron microprobe was done with five wavelength s...

Since the 1970s Bi2O3 has been successfully applied in metal-oxide varistors to introduce the nonlinear variable impedance into ZnO ceramics. For good electrical performance of the varistor a homogeneous microstructure is essential. The basis of the varistor's microstructure is the ZnO grains that are separated by an inter-granular layer formed by...

The role of aluminium oxide is investigated in an attempt to obtain low residual voltage ZnO varistors fabricated in the traditional way. The samples were sintered at three different temperatures: 1150, 1200, and 1250 °C for three different times: 1, 2, and 3 h. The effect of aluminium additions, in the range of 500–10,000 ppm, on the characteristi...

Since the 1970s Bi2O3 has been successfully applied in metal-oxide varistors to introduce the nonlinear variable impedance into ZnO ceramics. For good electrical performance of the varistor a homogeneous microstructure is essential. The basis of the varistor's microstructure is the ZnO grains that are separated by an inter-granular layer formed by...

ZnO-Bi2O3-based varistor samples doped with 0.45 mol% of Y2O3 and varying amounts of Sb2O3 in the range from 1.8 to 0.0 mol% were fired at 1230 degreesC. Only in the samples co-doped with Sb2O3 did doping with Y2O3 resulted in the formation of a fine-grained Bi-Zn-Sb-Y-O phase (the Y2O3-containing phase) at the grain boundaries, which very effectiv...

In low-voltage varistor ceramics, the phase equilibrium and the temperature of liquid-phase formation are defined by the TiO2/Bi2O3 ratio. The selection of a composition with an appropriate TiO2/Bi2O3 ratio and the correct heating rate is important for the processing of low-voltage varistor ceramics. The total amount of added Bi2O3 is important as...

Single crystals of KNbO3 and NaNbO3 were selected from the limited number of suitable alkali compounds that are available and evaluated as possible reference materials for the electron-probe microanalysis (EPMA) of alkaline niobates with a composition described by the general formula K1−XNaXNbO3. The EPMA study verified that KNbO3 and NaNbO3 single...

ZnO–Bi2O3-based varistor samples doped with 0.45 mol% of Y2O3 and varying amounts of Sb2O3 in the range from 1.8 to 0.0 mol% were fired at 1230 °C. Only in the samples co-doped with Sb2O3 did doping with Y2O3 resulted in the formation of a fine-grained Bi–Zn–Sb–Y–O phase (the Y2O3-containing phase) at the grain boundaries, which very effectively hi...

Varistor ceramics added with Ba-Bi and Ti is distinguished by enhanced mechanical and electrical features in comparison to the typical multicomponent ZnO ceramics. In the case of typical varistor ceramics during heating to sintering temperature forms the Bi-Sb-Zn pyrochlore phase which reacts with ZnO delivering Bi2O3 fraction in much volume. Bi 2O...