Bulk Ceramic Samples Research Articles

Synthesis of titanium diboride by electric arc plasma in air

The paper reports data that demonstrate the feasibility of vacuum-free electric arc synthesis of titanium diboride. An optimal energy mode was found to synthesize submicron titanium diboride powder with the hexagonal lattice parameters a = 3.03 ± 0.04 Å, c = 3.23 ± 0.04 Å with no impurity crystal phases in its composition. A bulk ceramic sample with relative density of 99.1 % and hardness of 18 GPa was consolidated from the synthesized powder. The powder and bulk ceramic samples were analyzed by scanning electron microscopy and transmission electron microscopy. Structure of the synthesized material has a positive effect on the densification of the material. The sintered grains already formed in the process of synthesis under the influence of external pressure and heating from the current flow sinter each other, forming a single target structure with a minimum number of pores, of oxide impurities. Raman spectroscopy was employed to analyze the homogenized precursor mixture, synthesized powder, and TiB2-based bulk ceramic sample. The obtained Raman spectrum of sintering powder is characteristic of TiB2-based materials with a low concentration.

Influence of grain size on electromechanical properties of (Ba,Ca)(Zr,Ti)O3: A multiscale analysis using spark plasma sintering and aerosol deposition

The piezoelectric and ferroelectric properties of aerosol deposited (AD) thick ceramic films are significantly reduced in comparison to bulk materials, which is assumed to be largely related to the nanometer-sized grains (∼0.01 μm) observed in the resulting microstructures. This work, therefore, focuses on understanding the role of grain size in electromechanical properties within the range of AD films based on Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT). In a comprehensive compilation of the piezoelectric constant (d33) of samples from various studies the grain size dependency of the d33 was shown for the lead-free ferroelectrics BCZT, BaTiO3, and (K,Na)NbO3. In this, it can be seen that no BCZT sample with a grain size below 0.4 μm was analyzed regarding their d33 before, thereby leaving a gap to the grain size of AD films. In this study, the grain size of ceramic bulk samples was varied using spark plasma and conventional sintering (0.1 μm – 11 μm) and their properties compared to those of AD films. To enable the fabrication of bulk samples in the same range as AD films, a hydrothermal powder with an average particle size of 0.075 μm was synthesized. A continuous increase of the permittivity, the polarization, and the piezoelectric coefficient was observed through grain size increase. These results suggest that the grain size of AD films needs to be enhanced to improve their properties. Importantly, the insights of this multiscale analysis on the grain size can help to tailor also the properties of other BCZT films and bulk samples.

Properties of ferroelectric composites in the microwave range

Ferroelectric ceramics of barium titanate and its solid solutions have found wide applications in technology, while compositions of a binary system with strontium titanate are most in demand. Electrically controlled components based on the barium titanate – strontium titanate ferroelectric ceramics are widely used in accelerator technology and the use of these materials is relevant at the present time. In the microwave range, composites based on the solid solution system barium titanate – strontium titanate ВаxSr1–xTiO3 (BST). Ferroelectric samples based on ВаxSrx–1TiO3 compound, where x = 0; 0.1; 0.3; 0.5; 0.7 were obtained using a conventional ceramic technology. The temperature dependences of the electrical properties of bulk ceramic samples based on ferroelectric composites were received in the temperature range 100°C to 350°C at a frequency of 1 kHz. It has been established that dielectric parameters significantly depend on the BaTiO3 content in BST compositions. To carry out a research in the frequency range from 0.1 to 8.5 GHz, an experimental setup was manufactured for measuring the electrical properties of ferroelectric materials based on an Agilent E5071C vector analyzer and a microstrip line. To conduct temperature studies, a microstrip line with a controlled sample was placed in a heat, cold and moisture chamber of the Bench-Top SU-261 series, in which it has been heated up to 60°C. The amplitude-frequency characteristics of the transmission coefficient (S21) of samples when heated from 20 °C to 60°C with an interval of 10 degrees were studied. The resonant frequency and quality factor of the resonator have been determined from the amplitude-frequency characteristic. Based on the value of the resonant frequency and the geometric dimensions of the sample, the dielectric constant of the sample material was calculated. It has been shown that with increasing barium titanate content (x = 0.1–0.3), the dielectric constant of the samples under study increases, and the resonant frequency shifts to lower frequencies. For samples with a barium titanate content of 50% and higher (x≥0.5), there are no resonance dependences and strong absorption of electromagnetic waves is observed. It has been established that with increasing temperature, the resonant frequency of composite material samples shifts to higher frequencies. Frequency dispersion of the dielectric constant is observed, which indicates the relaxor properties of the ceramic samples under study. Experimental investigations were carried out using a microwave strip line, a coaxial measuring cell and a capacitive converter; this made it possible to measure the dielectric constant of materials with values of more than several hundred in the microwave range and significantly reduce the control time when conducting thermal studies. It was shown that with a change in temperature, the electrophysical properties of the samples change significantly, which can be used in various systems and devices to change the reflection coefficient and phase of the electromagnetic wave.

Modified (Ba,Sr)(Sn,Ti)O3 via hydrothermal synthesis for electrocaloric application

Electrocaloric cooling systems require components with large entropy change at the desired working temperature, high electric breakdown strength and low dielectric losses. We here report on hydrothermal synthesis (HTS) route for preparation of lead-free electrocaloric (EC) material Ba0.82Sr0.18Sn0.065Ti0.935O3 (BSSnT-18-6.5) with a median particle size of d50 = 150 nm. Influence of molar ratio (Ba,Sr):(Sn,Ti) on the purity and particle size of hydrothermally synthesized powders is investigated. The sintering behavior and the resulting microstructure of bulk ceramic samples prepared with HTS powders as well as their dielectric, ferroelectric, and electrocaloric properties are analyzed and discussed in detail. By using HTS powders we could significantly reduce sintering temperature from 1400 °C to 1275 °C. Samples prepared with a molar ratio (Ba,Sr):(Sn,Ti) of 1.6 show a maximum EC temperature change |ΔTEC| of 0.59 K around 30 °C with a broad peak of |ΔTEC| > 0.3 K in the temperature range from 5 °C to 65 °C under an applied electric field change of 5 V μm−1. Our results show that hydrothermal synthesis is well suited to produce starting powders of lead-free electrocaloric materials for future fabrication of multilayer ceramic (MLC) components.

Influence of Sintering Additives on Modified (Ba,Sr)(Sn,Ti)O3 for Electrocaloric Application

This paper reports on the influence of sintering additives CuO and MgO on the recently developed lead-free electrocaloric (EC) material Ba0.82Sr0.18Sn0.065Ti0.935O3 (BSSnT-18-6.5). Details on the sintering behavior and the resulting microstructure of bulk ceramic samples prepared through solid-state synthesis and their dielectric, ferroelectric, and electrocaloric properties are presented. On the one hand, the addition of CuO (xCuO = 2%) significantly reduced the sintering temperature from 1400 °C to 1150 °C. On the other hand, the addition of MgO (xMgO = 1%) dramatically reduced the average grain size from 40 µm to 0.4 µm, leading to an increase in dielectric breakdown strength from 4.4 V µm−1 to 7.7 V µm−1. Thus, BSSnT-18-6.5 with the addition of MgO to bulk ceramic samples could achieve maximum EC temperature changes (|ΔTEC|) of 0.27 K around 30 °C with almost no aberration within a broad temperature range from 5 °C to 50 °C under an applied electric field change of 5 V µm−1. The results show the potential of this material for the fabrication of multilayer ceramic (MLC) components for future electrocaloric applications.

Effect of Free Cross-Linking Rate on the Molding of Bulk SiOC Ceramics

Polymer-derived ceramics (PDCs) have many advantages in ceramic molding and ceramic properties, but because of the obvious volume shrinkage in the process of precursor transformation into ceramics, it is easy for defects to appear in the forming process of bulk PDCs. Herein, theoretical analyses and experimental studies were carried out to improve the quality of sintered samples and realize the parametric design of raw materials. Firstly, based on the HPSO/D4Vi cross-linking system, the mathematical model of the free cross-linking ratio was established, and the theoretical value was calculated. After that, the samples with different free cross-linking rates were heated at 450 °C and 650 °C for different holding times. It was found that the free cross-linking ratio (α) had a significant impact on the weight loss of the samples. When the difference of the α value was 10%, the difference of the samples' weight loss ratio could reach 30%. Finally, the morphology of sintered products with different α values was analyzed, and it was found that obvious defects will occur when the free cross-linking ratio is too high or low; when this value is 40.8%, dense and crack-free bulk ceramics can be obtained. According to analysis of the chemical reaction and cross-linking network density during sintering, the appropriate value of the free cross-linking ratio and reasonable control of the cross-linking network are beneficial for reducing the loss of the main chain element and C element, alleviating the sintering stress, and thus obtaining qualified pressureless sintered bulk ceramic samples.

Quantitative Characterization of Local Thermal Properties in Thermoelectric Ceramics Using "Jumping-Mode" Scanning Thermal Microscopy.

Thermoelectric conversion may take a significant share in future energy technologies.Oxide-based thermoelectric composite ceramics attract attention for promising routes for control of electrical and thermal conductivity for enhanced thermoelectric performance. However, the variability of the composite properties responsible for the thermoelectric performance, despite nominally identical preparation routes, is significant, and this cannot be explained without detailed studies of thermal transport at the local scale. Scanning thermal microscopy (SThM) is a scanning probe microscopy method providing access to local thermal properties of materials down to length scales below 100 nm. To date, realistic quantitative SThM is shown mostly for topographically very smooth materials. Here, methods for SThM imaging of bulk ceramic samples with relatively rough surfaces are demonstrated. "Jumping mode" SThM (JM-SThM), which serves to preserve the probe integrity while imaging rough surfaces, is developed and applied. Experiments with real thermoelectric ceramics show that the JM-SThM can be used for meaningful quantitative imaging. Quantitative imaging is performed with the help of calibrated finite-elements model of the SThM probe. The modeling reveals non-negligible effects associated with the distributed nature of the resistive SThM probes used; corrections need to be made depending on probe-sample contact thermal resistance and probe current frequency.

Titanium-doped LiAlO2 ceramics for neutron scintillation

A series of bulk ceramic samples of titanium-doped LiAlO2 with doping concentrations of 0.05, 0.1, 0.5 and 1.0 at% were prepared using a sol-gel method. The LiAlO2:Ti samples showed emission in two spectral regions around 380 and 765 nm associated with the CT transition of Ti4+ and the d-d transition of Fe3+ impurities, respectively. The sample composition with 0.5 at% doping concentration exhibited the highest emission intensity. Furthermore, dense ceramic samples with 0.5 at% Ti-doping were prepared using spark plasma sintering. These samples exhibited intense CT luminescence of Ti4+ at 380 nm with a decay time of approximately 2.3 μs, while the emission of Fe3+ impurities was mostly suppressed.

Ash and Slag Waste Processing in Self-Shielded Atmospheric DC Arc Discharge Plasma.

In this paper, we report the experimental results obtained in slag waste processing by direct current arc discharge initiated in ambient air. The method does not employ vacuum and gas equipment, therefore increasing the energy efficiency of processing. Plasma processing of coal slag was performed at different arc exposure times: 5, 10, 15, 20, and 25 s. The obtained materials contained a significant amount of graphite, which was removed through combustion. The micropowder based on silicon carbide and aluminum nitride was obtained and then sintered by spark plasma. The bulk ceramic samples based on silicon carbide with the hardness of ~10.4 GPa were finally fabricated.

Tailoring electrocaloric properties of Ba1-xSrxSnyTi1-yO3 ceramics by compositional modification

This paper presents compositional modifications on lead-free material system based on barium titanate to optimize its electrocaloric (EC) properties. By addition of strontium and tin we prepared solid solutions of Ba1-xSrxSnyTi1-yO3 (BSSnT-100∙x-100∙y) which allow for shifting of maximum EC effect to room temperature as well as broadening the temperature range of high EC temperature changes ΔTEC. Bulk ceramic samples of BSSnT were prepared by solid-state reaction route and the influence of Sn:Sr ratio on dielectric and ferroelectric properties was investigated. The EC temperature change was measured directly using resistance welded thermocouple wires. Most promising results could be achieved for BSSnT-18−6.5, which showed a maximum ΔTEC of 0.49 K around 30 °C with ΔTEC > 0.3 K in the temperature range from 10 °C to 50 °C under a comparatively low electric field change of 2 V μm−1.

Synthesis and properties of lead-free BNT-BT-xCZ ceramics as high-temperature dielectrics

Bulk ceramic samples of the perovskite series (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xCaZrO3 with 0 ≤ x ≤ 0.2 were prepared using the conventional solid-state route. It is shown that careful characterization of Bi2O3 raw materials is essential to avoid deviations from the nominal composition. X-ray diffraction analysis reveals formation of perovskite main phase, and a relaxor-like response of the relative permittivity over temperature was observed. Flattening of the permittivity-temperature curves is observed with increasing CaZrO3 fraction, while maintaining low dielectric losses over a wide temperature range. Samples with x = 0.2 exhibit a temperature-stable permittivity of εr ≈ 600 (Δε’r/ε‘r,mid ≈ 10 % between -80°C and 300°C) along with small dielectric losses (tan δ < 0.02 between -55°C and 265°C) at 1 kHz. These attributes qualify these compositions as suitable high temperature capacitor dielectric materials.

Advanced Arc Plasma Synthesis of Biomorphic Silicon Carbide Using Charcoal and Silicon Dioxide in Air

This work presents the results revealing the possibility of obtaining a cubic phase of silicon carbide with features of a biomorphic structure. Renewable plant raw materials were used as a source of carbon, in particular, pyrolyzed sawdust, which is a waste of a timber enterprise. Silicon dioxide powder was used as a source of silicon. The synthesis was realized using DC arc discharge plasma initiated in an open air. In this case, the oxidation of the synthesis products was prevented due to the effect of the reaction volume self-shielding from atmospheric oxygen. It was possible due to the generation of protective gaseous medium predominantly consisting of carbon dioxide and monoxide. The dependences of the product phase composition on the supplied energy and composition of initial components were established. The synthesis product was characterized by a significant excess of carbon, which was a caused by the erosion of the electrodes. After removal of chemically unbound carbon from synthesis product by annealing in an atmospheric furnace at 850 °C, obtained powder was sintered by the spark plasma sintering method. In the result, a bulk ceramic sample was obtained in which the only one crystalline phase of silicon carbide with a lattice parameter of 4.359 Å was identified.

Low-temperature sintering, dielectric performance, and far-IR reflectivity spectrum of a lightweight NaCaVO4 with good chemical compatibility with silver

As one of the candidates of low-temperature cofired ceramics (LTCC), the sintering behavior, dielectric properties, and silver chemical compatibility of NaCaVO4 were studied. The bulk ceramic samples were densified well at a low sintering temperature of 720 oC with an optimal bulk density of 2.87 g/cm3. Excellent microwave dielectric properties with a low relative permittivity εr ~ 9.9, a high quality factor Q × f ~ 31,600 GHz, and a temperature coefficient of resonance frequency τf ~ -66.5 ppm/°C were achieved at 11.5 GHz. The far infrared reflectivity spectra revealed the intrinsic dielectric properties (relative permittivity of 8.34 and dielectric loss of 2.7×10-4) are comparable to the measured values. The absence of chemical reaction between NaCaVO4 and silver at firing temperature, evidenced by X-ray diffraction and energy dispersive spectroscopy indicated the potential prospect for LTCC application. Furthermore, the very low density of NaCaVO4 opens up an avenue for its potential applications in light-weight devices.

Multi-component PZT ceramics obtained by mechanochemical activation and conventional ceramic technology

In the paper, the multi-component PZT-type ceramics doped with Mn4+, Sb3+, W6+ and Ni2+ were investigated. The following chemical composition was selected: Pb(Zr0.49Ti0.51)0.94Mn0.01Sb0.03W0.015Ni0.01O3. The ceramic powders were synthesized by two methods: (i) the classical technological method using powder calcination and (ii) mechanochemical synthesis at room temperature. Densification of the powders (sintering) was carried by free sintering method. In the case of the mechanochemical activation, the development of the synthesis has been monitored by XRD and SEM investigations after different milling periods (25 h, 50 h and 75 h). From the obtained powder, the bulk ceramic samples have been prepared by uniaxial pressing and subsequent sintering. The ceramic multi-component PZT-type samples were characterized in wide temperature range by DTA, TG, DC electrical conductivity, XRD, SEM and EDS (energy-dispersive spectrometry) methods, and their ferroelectric, dielectric and piezoelectric properties were studied. At the work, a comparison of test results for samples obtained by two methods was made. The X-ray investigations confirmed that the obtained material exhibits a perovskite-like structure with a tetragonal phase (close to the morphotropic area). The detailed results of the multi-component PZT-type ceramics predispose these materials in microelectronic applications, for example, as element of the actuators and piezoelectric transducers. The application of the mechanochemical synthesis to obtain the PZT-type materials allows to shorten the time of the technological process, and at the same time not to reduce the electrophysical properties of ceramic samples.

Effects of lanthanum doping on electrical and electromechanical properties of (Pb1−xLax)(Zr0.70Ti0.30)O3 ceramics

In this study, the effect of La doping on the structural and electrical properties of lead zirconate titanate (Pb1−xLax)(Zr0.70Ti0.30)1−x/4O3 (PLZT) ceramics have been investigated where the lanthanum content were 8.0, 8.6 and 9.0 mol%. Bulk ceramic samples were synthesized via conventional solid-state reaction method. All of the PLZT ceramic samples exhibited a dispersive dielectric behavior. The maximum dielectric constants and the Curie temperature were found to decrease with increasing La content. The dielectric constants at room temperature were measured as 4069, 4112 and 3932, respectively. The Curie temperature (Tc) at 100 kHz was determined as 94 °C, 88 °C and 82 °C, respectively. The polarization versus electric field results indicated that an antiferroelectric-like character was observed at 8 mol% La-doping. However, further addition of La led to the progressive development of relaxor-like slim and slanted hysteresis loops, which still have a double hysteresis behavior. This indicated that La-doping stabilized the antiferroelectric character. The maximum and remanent polarization values and the field induced strain values of ceramics decreased with increasing La content, whereas the measured energy density and the efficiency was increased. The temperature dependence of the properties indicated a drop of ~ 33% with increasing temperature from 25 to 85 °C.

LaMgAl11O19 synthesis using non-hydrolytic sol-gel methods

Polycrystalline LaMgAl11O19 (LMA) was prepared by four different non-hydrolytic sol-gel methods. From stable solutions, four powder precursors containing an amorphous and nanocrystalline phase with specific reactivity were obtained. The particle size, morphology, thermal behaviour, and phase composition of the powder precursors were studied using DLS, TEM, DSC/TG and XRD. Bulk ceramic samples containing LMA were prepared at 1200 °C for 16 h and examined in terms of phase purity and microstructure using XRD, SEM, and TEM. Raman spectroscopy of pure LMA was used to study the structure in detail. A mechanism of LMA formation and a relation between powder precursor properties and final phase composition is proposed. These findings may be useful for designing modern technologies for fabrication of LMA for optical or protective coating applications.

Electrochemical Degradation Caused By Mechanical Damage in All Solid State Battery Based on Al2O3 doped Li7La3Zr2O12

All solid state lithium ion batteries consisting of solid electrodes and a Li ion conductive solid electrolyte have been expected to overcome the safety problem of present lithium ion batteries including flammable non-aqueous solvent . Solid solid interface contact between electrode and electrolyte layers also prevents the formation of the side reaction which is adverse for the lifespan of liquid batteries. However, the degradation of all solid state batteries(ASSBs) still exists even though it shows higher reliability compared to the traditional liquid batteries. Li7La3Zr2O12 solid electrolyte is one of the promising electrolytes for all solid state battery due to its high Li ion conductivity and stability against Li metal anode. For LiCoO2 cathode, decreasing the lithium concentration during charging process will lead to substantial repulsive forces between the O2 − ions in adjacent layers. It has been observed by Luo et al. that the maximum volume change rate LiCoO2 could be up to ~ 4.27% at the fully charging end. We suspect that the cathode interface formation in combination with the mechanical expansion ion provokes a contact loss between active material and solid electrolyte. We investigate the interface behavior at the cathode and demonstrate the important role of the interface between the active materials and the solid electrolyte for the battery performance. As solid electrolytes show quite limited plasticity and are unable to flow or infiltrate pores—in contrast to their liquid counterparts—mechanical contact loss due to irreversible shape changes of the LiCoO2 material is expected to have a significant contribution to the observed interfacial resistance. We reveal that the large volumetric change during the charge-discharge cycle and the resultant cracks are the primary mechanism of cyclic degradation of the ASSBs with rigid contact between cathode and solid electrolyte layers. Li7La3Zr2O12 bulk ceramic samples were fabricated by conventional solid-state reaction. The starting materials, Li2CO3, La(OH)3, γ-Al2O3 and ZrO2, were mixed by planetary ball-milling, and then calcinated at 800 °C for 10 h and 900°C for 10h. The calcinated powders were pressed into pellets and sintered at 1150 °C for 36 h in air. The cathode electrodes consist of 90 wt % active material and 10 wt % polyvinylidendifluoride solved in N-methyl pyrrolidone as a binder. No electrolyte material is added to purely focus on volume change behavior of the LiCoO2. Li foil was then attached on to the other side of the Li7La3Zr2O12 pellet as anode. All solid state battery with Li/Al2O3 added Li7La3Zr2O12 /LiCoO2 configuration was fabricated and its electrochemical properties were tested. The cycle life of the battery has been examined at temperature of 150 °C. All solid state cells (Li | Li7La3Zr2O12 | LiCoO2) were galvanostatically cycled within a potential window of 3.0–4.3 V vs Li/Li+ at 150 °C. The charge/discharge current density is set as 5 μA·cm− 2. All capacity was reported based on the mass of LiCoO2. The morphology of the electrode/electrolyte interface of the battery was observed using field emission-scanning electron microscopy (SEM). The theoretical electrochemical capacity of LiCoO2 is 137 mAh g−1, which corresponds to 0.5 Li per CoO2. The charge and discharge capacities of this battery were 12.6 mAh g−1, which corresponded to about 10% of the theoretical capacity. However, the corresponding discharge capacity is 2.7 mAh g−1 with columbic efficiency of 21%, indicating that most of lithium deintercalated from the cathode could not return to the lattice. The discharge capacity gradually decays and the capacity retention is 3% after 5 cycles. It can be seen that the first cycle is crucial for the overall capacity retention, as the most severe loss in capacity occurs in the first cycle. Such a strong capacity loss is not found when using LiCoO2 in a liquid electrolyte cell, suggesting that it is characteristic for the solid state environment. The attached figure presents the cross sectional SEM images of the interface between the cathode and the solid electrolyte. The results indicate that the destructive damage of cracks originated from the volume change of LiCoO2 layer is responsible for the degradation of cell during cycling. Figure 1

Tuning of BiFeO3 multiferroic properties by light doping with Nb

Bulk ceramic samples of BiFeO3 were light doped (up to 1%) with Nb5+ in the place of Fe3+ (B-site doping) and their multiferroic properties were investigated using XRD, SEM, polarization (PMTS) and magnetization (SQUID) techniques. It is shown that even the small percentages of doping can notably change electric and magnetic behavior. Electric conductivity differs by two orders of magnitude between samples doped with 0.2% and 1% Nb. The ferroelectric behavior strongly depended on conduction mechanism, and transition from space-charge-limited current (SCLC) conduction to trap-filled limited (TFL) conduction regime reflected on a change in hysteresis patterns, particularly for the samples with 0.2% and 0.5% Nb. Separation of ZFC-FC magnetization curves occurred for all Nb concentrations and increased with Nb doping. Weak ferromagnetic behavior and the increase of remnant magnetization with Nb concentration was observed from the hysteresis measurements. Coercive field changed drastically compared to the pure BiFeO3, namely, the sample with 1% Nb exhibited very high coercive magnetic field of ~ 10 kOe.

High Temperature Superconductors (${\rm Y}_{1-x}{\rm Nd}_{x}$ )Ba2Cu3O7-δ Obtained by Acetate Method

Bulk ceramic samples with chemical composition (Y 1-x Nd x )Ba 2 Cu 3 O 7-δ , where x = 0, 0.1, 0.2, 0.5, and 1 were sintered by a proposed acetate method. The samples were then submitted to structural characterization by X-ray diffraction with crystal structure refining using the Rietveld method. AC electrical resistivity measurements from ambient temperatures down to 4.2 K were performed, as well as magnetic measurements of magnetic moment as function of temperature and magnetic hysteresis loop. Results have shown superconductivity with critical temperatures of about 91 and 60 K for pure YBa 2 Cu 3 O 7-δ (x = 0) and pure NdBa 2 Cu 3 O 7-δ (x = 1) samples, respectively. Scanning electron microscopy images were also analyzed, revealing a regular parallel-piped grain shape. The proposed method showed as an advantage to reduce the grinding time without any considerable degradation on structural or superconducting properties of pure YBa 2 Cu 3 O 7-δ (x = 0) or pure NdBa 2 Cu 3 O 7-δ ( x = 1), as related to samples prepared by a conventional solid state route.

Structure and properties of ZrB2, ZrSiB and ZrAlSiB cathode materials and coatings obtained by their magnetron sputtering

The ceramic ZrB2, ZrSiB, and ZrAlSiB cathodes were manufactured by means of self-propagating high-temperature synthesis (SHS). The parameters of SHS process including dependence of the combustion temperature and rate on the initial temperature of the reaction mixtures, as well as values of effective activation energy were estimated. Cathodes were subjected to the magnetron sputtering in the argon atmosphere. The structure and properties of cathodes and coatings were studied by means of X-ray diffraction, scanning electron microscopy, energy-dispersive and glow discharge optical emission spectroscopy. Bulk ceramic samples and coatings were characterised in terms of their hardness, elastic modulus, elastic recovery, density, and residual porosity. Results obtained shows that cathodes posses homogeneous structure with low porosity level in range 2-6% and hardness between 10 and 17 GPa. Coatings demonstrate dense defect-free structure and contain nanocrystallites of h-ZrB2 phase. The grain size and hardness decrease from 8 down to 2 nm and from 37 down to 16 GPa with the addition of the silicon and aluminum dopes.