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    Optical and electrical performance of translucent BaTiO3-BaSnO3 ceramics
    (ELSEVIER SCI LTD, 2024-08-15) Bijalwan, Vijay; Kaštyl, Jaroslav; Erhart, Jiří; Prajzler, Vladimír; Tofel, Pavel; Sobola, Dinara; Velazquez, Jose J.; Galusek, Dušan; Maca, Karel
    Lead-free piezoceramic with the composition of 0.89BaTiO(3)-0.11BaSnO(3) (BT-11BS) was prepared by solid-state reaction followed by conventional sintering achieving nearly full density. The influence of sintering temperature on electrical properties were thoroughly investigated, implying a significant role in achieving best properties, which were obtained between 1420 and 1440 degrees C. The addition of SnO2 in BaTiO3 solid solution promoted grain growth, eventually resulting in the grain sizes between 145 and 216 mu m. An ultra-high dielectric permittivity >5.0 x 10(4) and related dielectric loss of 3.1 % at similar to 40 degrees C was achieved. A high value of quasi-static piezoelectric constant (d(33)) of 693 pC/N and the converse piezoelectric constant (denoted as d(33)*) reached a value of up to 831 pm/V in the frequency range between 10 and 110 Hz. The transmittance of similar to 25 % in the visible region and similar to 40 % in the infrared region together with good electromechanical properties showcasing a unique combination for this material.
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    Basic microstructural, mechanical, electrical and optical characterisation of BaTiAl6O12 ceramics
    (Elsevier, 2024-06-27) Drdlík, Daniel; Mařák, Vojtěch; Klement, Róbert; Tofel, Pavel; Drdlíková, Katarina; Hadraba, Hynek; Chlup, Zdeněk
    In progressive particle or layered composites based on a combination of BaTiO3 and Al2O3, serving as e.g. ceramic harvesters, new phases are formed during heat treatment. The dominant one is BaTiAl6O12. This study provides information about the microstructural, mechanical and optical properties of the BaTiAl6O12 ceramics. The evolution of the phases during the solid-state reaction synthesis of the BaTiAl6O12 was monitored. The fully dense samples prepared by Spark Plasma Sintering had indentation Vickers hardness and indentation elastic modulus within ranges of 10.1 – 13.7 GPa and 132.0 – 187.0 GPa, depending on loading force. The three-point bending tests of the BaTiAl6O12 samples resulted in flexural strength of 129.9 MPa and fracture toughness of 1.8 MPa.m1/2.The sample showed blue broad-band emission under UV excitation due to the charge-transfer transition of the Ti4+ and defect sites. The BaTiAl6O12 evinced low permittivity (') = 16 and dielectric loss (tan ) < 0.0003 at a frequency 1 kHz.
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    Improving the strength of -TCP scaffolds produced by Digital Light Processing using two-step sintering
    (ELSEVIER SCI LTD, 2024-04-01) Paredes Sánchez, Claudia Isabel; Roleček, Jakub; Miranda, Pedro
    Digital Light Processing is combined with two-step sintering to obtain bioactive scaffolds with improved strength and mechanical isotropy. Highly loaded photosensitive suspensions were prepared from beta-TCP powder to create scaffolds consisting of interpenetrating struts with two different designs. Two sintering methods were used: conventional sintering (CS) and two-step sintering (2SS). The latter resulted in a microstructure with uniformly shaped grains and reduced porosity. Their compressive strength was determined by uniaxial testing under two different load configurations, with the force applied parallel or perpendicular to the building plane of the scaffolds. Design optimisation and fine-tuning of the sintering process helped in reducing the presence of interlayer defects and minimise the shear-dominated fractures. Isotropic fracture behaviour was achieved, with similar central values of the Weibull distribution (49 +/- 1 MPa vs. 51 +/- 1 MPa) along both testing directions, showing a great potential for their use in load-bearing bone tissue engineering applications.
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    Evaluating the suitability of fast sintering techniques for the consolidation of calcium phosphate scaffolds produced by DLP
    (ELSEVIER SCI LTD, 2023-11-01) Paredes Sánchez, Claudia Isabel; Roleček, Jakub; Pejchalová, Lucie; Spusta, Tomáš; Salamon, David; Miranda, Pedro
    Porous scaffolds were fabricated via Digital Light Processing (DLP) from beta-TCP powder and sintered by conventional sintering in air (CSA), rapid sintering in air (RSA) and pressure-less spark plasma sintering in vacuum (pl-SPS), at four different temperatures: 1200, 1300, 1400 and 1500 degrees C. Each sintering strategy resulted in scaffolds with different phase composition, microstructure and mechanical properties. Long dwell times or high temperatures were required to achieve a complete beta ->alpha transformation, and rapid cooling rates avoided the reverse transformation. The presence of graphite in the sintering chamber played a crucial role in stabilising the alpha-TCP phase, phase prevailing in SPS-treated scaffolds, hindered their densification and avoided the generation of transformation-induced cracks. All scaffolds exhibited compressive strengths within the range of cancellous bone, with the highest average value of 22 +/- 4 MPa achieved by the RSA scaffolds sintered at 1300 degrees C, thanks to their greater densification and fine microstructure.
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    Dilatometric and microstructural study of particle and functionally graded composites based on hydroxyapatite and crystalline bioglass
    (2023-10-23) Drdlík, Daniel; Drdlíková, Katarina; Maca, Karel
    Hydroxyapatite (HA) and bioglass (BG) ceramics have become of prime importance in bone tissue engineering. Besides the appropriate composition, the microstructure of bone replacement plays a crucial role. In the present work, particle composites and functionally graded material (FGM) based on HA and BG prepared by electrophoretic deposition were thoroughly characterised in terms of the preparation method, sintering process, phase composition and microstructure. The sintering was monitored by high-temperature dilatometry in two directions, the sintering rates were calculated, and the overall sintering process was discussed. The SEM showed the continuous change in the microstructure of FGM with gradual interconnected porosity favourable for bio-applications. The fundamental fractographic analysis proved the crack development in FGM related to the sintering process, and the recommendations for the reduction of the crack development were given. The phase transformations during thermal treatment were analysed using X-ray diffraction analysis and deeply discussed.