Investigations of the coupling of spin-orbital in MgTi2O4 by the magnetic entropy measurements

2014 ◽  
Vol 28 (29) ◽  
pp. 1450232 ◽  
Author(s):  
Yuanyuan Zhu ◽  
Rongjun Wang ◽  
Li Wang ◽  
Yong Liu ◽  
Rui Xiong ◽  
...  
Keyword(s):  
Single Phase ◽  
Entropy Change ◽  
Antiferromagnetic Order ◽  
Magnetic Entropy ◽  
Spin Orbital ◽  
Absolute Value ◽  
Spin Entropy ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Lower Temperature

Single phase MgTi 2 O 4 compound was synthesized by spark plasma sintering (SPS) method. The temperature dependence of the magnetic susceptibility and specific heat measurements show that MgTi 2 O 4 takes place in phase transition at 258 K. Magnetic entropy measurements show that the change of magnetic entropy ΔSM is positive and ΔSM increases more quickly than H2/3 near the transition; while ΔSM is negative and |ΔSM| (the absolute value) increases slowly with applied field increasing at lower temperature. The change of ΔSM at different temperature range is suggested to be related not only to spin entropy change, but also orbital entropy change. The magnetic phases of MgTi 2 O 4 are suggested to be Pauli paramagnetic, collinear antiferromagnetic and non-collinear antiferromagnetic order with temperature decrease.

scholarly journals Processing Conditions Optimization for the Synthesis and Consolidation of High-Entropy Diborides

2021 ◽  
Vol 23 (3) ◽  
pp. 213
Author(s):  
S. Barbarossa ◽  
M. Murgia ◽  
R. Orrù ◽  
G. Cao
Keyword(s):  
Single Phase ◽  
Processing Conditions ◽  
High Entropy ◽  
Temperature Conditions ◽  
Final Density ◽  
Plasma Sintering ◽  
High Temperature Synthesis ◽  
Surface Oxides ◽  
Spark Plasma ◽  
Lower Temperature

The fabrication by Spark Plasma Sintering (SPS) of bulk high entropy ceramics from powders obtained by Self-propagating High temperature Synthesis (SHS) is addressed in this work. The effect produced by the introduction of 1 wt.% of graphite to the powders before SPS is investigated under different temperature conditions. The final density and composition of sintered (Hf0.2Mo0.2Zr0.2Ti0.2Ta0.2)B2 and (Hf0.2Mo0.2Zr0.2Ti0.2Nb0.2)B2 ceramics are found to be negatively affected by the presence of oxide impurities in the powders. While product composition can be progressively improved when the temperature is increased from 1800 to 1950 °C, residual porosities remain relatively high if using additive-free powders. In contrast, the introduction of 1 wt.%C markedly allows for oxides elimination by carbothermal reduction mechanism. Products consolidation is correspondingly enhanced so that relative densities of about 97% are attained. Other than the latter effect, surface oxides removal also makes powders more reactive, thus the synthesis of single-phase products is promoted. In particular, fully homogeneous (Hf0.2Mo0.2Zr0.2Ti0.2Ta0.2)B2 ceramics are obtained at relatively lower temperature conditions (1850 °C).

Magnetocaloric Effect of LaFe11.5Si1.5C0.2 Sinters Prepared by SPS Process

2013 ◽  
Vol 849 ◽  
pp. 212-217
Author(s):  
Yuan Yuan Wu ◽  
Yi Long
Keyword(s):  
Particle Size ◽  
High Performance ◽  
Magnetic Entropy Change ◽  
Parent Compound ◽  
Entropy Change ◽  
Magnetic Entropy ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Magnetic Refrigeration Materials ◽  
Sintered Temperature

In order to make high performance magnetic refrigeration materials, Spark Plasma Sintering (SPS) process was introduced in the preparation of LaFe11.5Si1.5C0.2 materials. Results show that the size of the starting powder has a significant influence on the magnetic entropy change than the sintered temperature does. Finer starting powder induce a decomposition of 1:13 phase into α-Fe phase during sintered process. By controlling the particle size, the decomposition can be decreased. The maximum magnetic entropy change value of the sinters with the size of sutible starting powder is as same as the parent compound. Also, the hysteresis loss of the sinters decreased.

scholarly journals Fabrication and Characterization of Quinary High Entropy-Ultra-High Temperature Diborides

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 108-120
Author(s):  
Simone Barbarossa ◽  
Roberto Orrù ◽  
Valeria Cannillo ◽  
Antonio Iacomini ◽  
Sebastiano Garroni ◽  
...  
Keyword(s):  
High Temperature ◽  
Single Phase ◽  
Nominal Composition ◽  
High Entropy ◽  
Chemical Complexity ◽  
Alternative Processing ◽  
Plasma Sintering ◽  
High Temperature Synthesis ◽  
Spark Plasma

Due to their inherent chemical complexity and their refractory nature, the obtainment of highly dense and single-phase high entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5, and 98.2%, respectively) were successfully produced by spark plasma sintering (SPS) using powders prepared by self-propagating high-temperature synthesis (SHS). Although the latter technique did not lead to the complete conversion of initial precursors into the prescribed HE phases, such a goal was fully reached after SPS (1950 °C/20 min/20 MPa). The three HE products showed similar and, in some cases, even better mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values were found for the (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2 and the (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 systems, i.e., 28.1 GPa/538.5 GPa and 28.08 GPa/498.1 GPa, respectively, in spite of the correspondingly higher residual porosities (1.2 and 2.2 vol.%, respectively). In contrast, the third ceramic, not containing tantalum, displayed lower values of these two properties (25.1 GPa/404.5 GPa). However, the corresponding fracture toughness (8.84 MPa m1/2) was relatively higher. This fact can be likely ascribed to the smaller residual porosity (0.3 vol.%) of the sintered material.

scholarly journals Thermoelectric properties of Cu3SbSe3 with intrinsically ultralow lattice thermal conductivity

2014 ◽  
Vol 2 (38) ◽  
pp. 15829-15835 ◽  
Author(s):  
Kriti Tyagi ◽  
Bhasker Gahtori ◽  
Sivaiah Bathula ◽  
A. K. Srivastava ◽  
A. K. Shukla ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Solid State ◽  
Spark Plasma Sintering ◽  
Thermoelectric Properties ◽  
Solid State Reaction ◽  
Electrical Transport ◽  
Single Phase ◽  
Lattice Thermal Conductivity ◽  
Plasma Sintering ◽  
Spark Plasma

Intrinsically ultra-low thermal conductivity and electrical transport in single-phase Cu2SbSe3 synthesized employing a solid state reaction and spark plasma sintering.

Transparent mullite ceramic from single-phase gel by Spark Plasma Sintering

2009 ◽  
Vol 29 (13) ◽  
pp. 2705-2711 ◽  
Author(s):  
Guimin Zhang ◽  
Yucheng Wang ◽  
Zhengyi Fu ◽  
Hao Wang ◽  
Weiming Wang ◽  
...  
Keyword(s):  
Spark Plasma Sintering ◽  
Single Phase ◽  
Mullite Ceramic ◽  
Plasma Sintering ◽  
Spark Plasma

Nonstoichiometric Composition and Densification of CaRuO3 by SPS

2007 ◽  
Vol 352 ◽  
pp. 251-254 ◽  
Author(s):  
Nittaya Keawprak ◽  
Rong Tu ◽  
Takashi Goto
Keyword(s):  
Spark Plasma Sintering ◽  
Single Phase ◽  
Lattice Parameters ◽  
Second Phase ◽  
Nonstoichiometric Composition ◽  
Plasma Sintering ◽  
Spark Plasma

Calcium ruthenates were prepared in different ratios of Ru to Ca (RRu/Ca = 0.5～1.4) by spark plasma sintering. CaRuO3 in a single phase was obtained at RRu/Ca = 1.0. At RRu/Ca < 1.0, a mixture of CaRuO3 and CaO was obtained, whereas CaRuO3 with second phase of RuO2 was obtained at RRu/Ca > 1.0. The density at RRu/Ca < 1.0 were 80-85% and slightly increased with increasing RRu/Ca. The density significantly increased up to 95% with increasing RRu/Ca from 1.1 to 1.4, suggesting that the second phase of RuO2 was effective to densify CaRuO3. The density of CaRuO3 in a single phase was 82% at most. The lattice parameters of CaRuO3 decreased with increasing RRu/Ca from 0.7 to 1.0, showing a nonstoichiometric range of Ca1+δRuO3+δ.

Formation of in-situ reinforced microstructure in α–sialon ceramics I: Stoichiometric oxygen-rich compositions

2002 ◽  
Vol 17 (2) ◽  
pp. 336-342 ◽  
Author(s):  
Zhijian Shen ◽  
Hong Peng ◽  
Mats Nygren
Keyword(s):  
Hot Pressing ◽  
Single Phase ◽  
Transient Liquid Phase ◽  
Precursor Powder ◽  
Temperature Dependent ◽  
Consolidation Process ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Equiaxed Grains

The abnormal grain growth in α–sialon ceramics was investigated. The preparations had stoichiometric compositions on the oxygen-rich phase boundary, and they were stabilized by Y, Nd, Sm, Dy, and Yb, respectively. Specimens were prepared from α–Si3N4 as precursor powder by applying conventional hot pressing and a novel rapid consolidation process, namely spark plasma sintering (SPS). Single-phase α–sialon ceramics with in situ reinforced bimodal microstructure, i.e., large elongated grains embedded in a matrix consisting of small equiaxed grains, were obtained above 1750 °C in all systems compacted by SPS and above 1800 °C in systems stabilized by Nd and Sm but not Dy, Y, or Yb by a two-step hot-pressing procedure. It was observed that the formation of abnormally grown α–sialon grains was strongly temperature-dependent, indicating that it was encouraged by the formation of a transient liquid phase that stimulated the dissolution of any remaining nitride precursors and early formed small α–sialon grains and sequentially facilitated supersaturation by the α–sialon constituents. The presence of elongated grains improves fracture resistance in the obtained materials.

Magnetic, Magnetocaloric and Magnetoresonance Properties of (1-x)La0.7Sr0.3MnO3/xGeO2 (x=0, 0.15)

2019 ◽  
Vol 289 ◽  
pp. 170-176
Author(s):  
Tatiana Gavrilova ◽  
Ildar Gilmutdinov ◽  
Ivan Yatsyk ◽  
Tatiana Chupakhina ◽  
Julia Deeva ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Entropy Change ◽  
Magnetic Ordering ◽  
Entropy Change ◽  
Magnetic Entropy ◽  
Anisotropic Particles ◽  
X Ray Diffraction ◽  
Absolute Value ◽  
X Ray ◽  
Magnetic Resonance Spectra

0.85La0.7Sr0.3MnO3/0.15GeO2composite material and pure La0.7Sr0.3MnO3were investigated by X-ray diffraction, scanning electron microscopy, magnetometry and magnetic resonance methods. It was observed that both samples demonstrate the ferromagnetic properties, while the absolute value of the magnetization, the magnetic entropy change and the magnetic ordering temperature decrease in composite in comparison with pure La0.7Sr0.3MnO3. The magnetic resonance spectra of investigated (1-x)La0.7Sr0.3MnO3/xGeO2(x=0, 0.15) can be attributed to the superposition of magnetic resonance spectra from magnetically anisotropic particles with different orientations.

scholarly journals Application of Hydride Process in Achieving Equimolar TiNbZrHfTa BCC Refractory High Entropy Alloy

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1020 ◽  
Author(s):  
Bhupendra Sharma ◽  
Kentaro Nagano ◽  
Kuldeep Kumar Saxena ◽  
Hiroshi Fujiwara ◽  
Kei Ameyama
Keyword(s):  
Titanium Hydride ◽  
Single Phase ◽  
Strengthening Mechanism ◽  
High Entropy Alloy ◽  
Mechanically Alloyed ◽  
High Entropy ◽  
Plasma Sintering ◽  
Bcc Structure ◽  
Spark Plasma ◽  
Tih2 Powder

For the first time, an equiatomic refractory high entropy alloy (RHEA) TiNbZrHfTa compact with a single-phase body-centered cubic (BCC) structure was fabricated via a titanium hydride (TiH2) assisted powder metallurgy approach. The constituent pure Ti, Zr, Nb, Hf, and Ta powders were mechanically alloyed (MA) with titanium hydride (TiH2) powder. The resultant MA powder was dehydrogenated at 1073 K for 3.6 ks and subsequently sintered through spark plasma sintering (SPS). Additionally, TiNbZrHfTa counterparts were prepared from pure elements without MA with TiH2. It was observed that the compact prepared from pure powders had a chemically heterogeneous microstructure with hexagonal close packed (HCP) and dual BCC phases. On the other hand, despite containing many constituents, the compact fabricated at 1473 K for 3.6 ks via the hydride approach had a single-phase BCC structure. The Vickers microhardness of the TiNbZrHfTa alloy prepared via the hydride process was Hv 520 (±30). The exceptional microhardness of the alloy is greater than any individual constituent, suggesting the operation of a simple solid-solution-like strengthening mechanism and/or precipitation hardening. In addition, the heat treatments were also carried out to analyze the phase stability of TiNbZrHfTa prepared via the hydride process. The results highlight the substantial changes in the phase as a function of temperature and/or time.

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