C14 Type Research Articles

Hydrogenation and dehydrogenation cycle properties of Ti–Mn based alloy Ti0.93Zr0.07Mn1.15Cr0.35 in hydrogen gas

Hydrogenation and dehydrogenation cycle tests at 0 °C for Ti0.93Zr0.07Mn1.15Cr0.35 were carried out 2000 cycles and more in the hydrogen gas with purity of 99.99% and 99.99999%. The capacity maintenance rates at the 2000th cycle for the first cycle were 82% and 97% for each purity hydrogen gas, respectively. It was found that the cycle durability of this alloy depends on the gas purity. By the X-ray diffraction and light element analysis, it was confirmed that the C14 type crystal structure of this alloy was maintained but the nitrogen concentration in the sample with large capacity reduction was increased after the cycle test. The main factor of the decrease in capacity of this alloy is degradation due to reaction with impurity gas components such as nitrogen.

Hyperfine Magnetic Fields at the Nuclei of 57Fe in the Intermetallic System Zr1 –xScxFe2

Mossbauer studies of the anisotropy of hyperfine interactions (HFIs) of the 57Fe nuclei in the quasi-binary intermetallic system Zr1 –xScxFe2 (0 ≤ x ≤ 1) with the structure of the cubic Laves phase of the C15 type have been performed. Within the framework of the tensor description of the anisotropy of magnetic HFIs, taking the crystal and magnetic structure into account, the hyperfine parameters of the partial spectra have been expressed through the constant of the quadrupole interaction, the isotropic and anisotropic magnetic fields, and also the azimuthal and polar angles, which specify the orientation of the direction of the easy axis of magnetization (EA). It has been established that at temperatures of 87 and 297 K the EA deviates in the plane $$(1\bar {1}0)$$ from the crystallographic direction [111] by ~15°, and with an increase in the concentration x, the orientation of the EA almost does not change. The changes in the isotropic field and in the shift of the Mossbauer line have an anomalous character. With an increase in x, an increase can first be observed, and then, at x > 0.4, a decrease of the magnitude of the isotropic field can be observed. The shift of the Mossbauer line decreases with an increase in x; at x ~ 0.4, a bent is observed. This anomalous behavior of the isotropic field and of the shift correlates with a change in the lattice parameter and in the magnetic moment of the Fe atoms. The anisotropic field decreases linearly with an increase in the concentration of Sc atoms, while the constant of the quadrupole interaction almost does not change, ~1 mm/s.

Effect of Hydrogen on the Structure, Magnetic and Magnetocaloric Properties of Laves Phase Type-Compounds RE(Fe<sub>0.25</sub>Co<sub>0.75</sub>)<sub>2</sub>H<sub>y</sub> with RE = Ho and Er, y = 0.0, 3.0, 3.5

The crystal structure and overall magnetic properties of RE(Fe0.25Co0.75)2Hywith RE = Ho and Er, were analyzed versus y, the hydrogen content. The single phase C15 type compounds, synthesized using cold crucible HF melting, were hydrogenated and controlled using a PCI apparatus. The impact of hydrogen insertion on the cell parameter, the Curie temperature TCand the magnetization saturation were determined. All compounds and hydrides were found to be ferrimagnets, the magnetic moment of RE and 3d elements being opposite since Ho and Er belong to the 2ndrow of rare earth elements. Depending on the formula, a typical compensation point was in evidence. The 2ndorder character of the ferri ↔ paramagnetic transition was established using the Arrott plot method. Magnetization isotherms vs. magnetic field gives quantified results for the magnetic entropy variation by application of the Maxwell relation. Control of y, the hydrogen content, shows it is interesting for improvement of the MCE of the starting compounds. However increasing y leads to decreased TCat the lowest temperatures, suggesting potential cryogenic uses.

Compositional effects on the hydrogen cycling stability of multicomponent Ti-Mn based alloys

Intermetallic alloys such as AB, AB2, and AB5 type have been studied due to their capability to reversibly store hydrogen. These alloys exhibit varying hydrogen storage properties depending on the crystal structure and composition. Compositional modification is commonly known as an effective method to modify the alloys thermodynamic and kinetics for various applications such as metal hydride batteries, metal hydrides hydrogen storage and compression. However, the effects of the compositional modification on the cyclic stability of these alloys are not usually well studied.Here, the hydrogen cycling stabilities of Ti-Mn based alloys with C14 type structure are studied. Hyper-stoichiometry, stoichiometry and hypo-stoichiometry alloys were prepared accordingly: Ti30.6V16.4Mn48.7 (Zr0.7Cr0.8Fe2.8) (B/A = 2.19), Ti32.8V15.1Mn47.1 (Zr0.9Cr1.2Fe2.9) (B/A = 1.97) and Ti34.5V15.4Mn44.7 (Zr0.9Cr1.3Fe3.2) (B/A = 1.87). Whilst the hyper-stoichiometry alloy showed almost a stable (about 9% capacity reduction) hydrogen capacity after 1000 cycles of hydrogenation and dehydrogenation, the stoichiometry and hypo-stoichiometry alloys failed to hydrogenate after about 950 and 500 cycles respectively. A limited reduction in the calculated crystalline size of the alloys was observed before and after the hydrogen cycling, denoting that pulverisation plays a less significant role on the observed hydrogen capacity loss. In addition, a reduction in the B/A ratio from 2.19 to 1.82 (hyper to hypo-stoichiometry) encouraged the formation of more stable hydride and a higher level of heterogeneous lattice strain. Whilst a small loss of hydrogen capacity (9%) in the hyper-stoichiometry alloy was attributed to the trapped hydrogen, the complete loss of hydrogen capacity in the stoichiometry and hypo-stoichiometry alloys seemed to originate from the formation of stable hydride and the lattice distortion.

Thermal Stability of the HfNbTiVZr High-Entropy Alloy.

The multicomponent alloy HfNbTiVZr has been described as a single-phase high-entropy alloy (HEA) in the literature, although some authors have reported that additional phases can form during annealing. The thermal stability of this alloy has therefore been investigated with a combination of experimental annealing studies and thermodynamic calculations using the CALPHAD approach. The thermodynamic calculations show that a single-phase HEA is stable above about 830 °C. At lower temperatures, the most stable state is a phase mixture of bcc, hcp, and a cubic C15 Laves phase. Annealing experiments followed by quenching confirm the results from thermodynamic calculations with the exception of the Laves phase structure, which was identified as a hexagonal C14 type instead of the cubic C15 type. Limitations of the applied CALPHAD thermodynamic description of the system could be an explanation for this discrepancy. As-synthesized HfNbTiVZr alloys prepared by arc-melting form a single-phase bcc HEA at room temperature. In situ annealing studies of this alloy show that additional phases start to form above 600 °C. This indicates that the observed HEA is metastable at room temperature and stabilized by a slow kinetics during cooling. X-ray diffraction analyses using different cooling rates and annealing times show that the phase transformations in this HEA are slow and that completely different phase compositions can be obtained depending on the annealing procedure. In addition, it has been shown that the sample preparation method (mortar grinding, heat treatment, etc.) has a significant influence on the collected diffraction patterns and therefore on the phase identification and analysis.

Improved deformation behavior in Ti-Zr-Fe-Mn alloys comprising the C14 type Laves and β phases

Laves phase alloys are promising materials for several structural applications, but the extreme brittleness is the predominant shortcoming of a Laves matrix. One potential solution to overcome this shortcoming is to alloy Laves matrix with some soft matrix. A group of Ti-35Zr-5Fe-xMn (x = 0, 2, 4, 6, 8 wt%) alloys was cast with an aim to improve deformation in Laves alloy compositions. The phase and microstructure analyses reveal dual phase matrices, including a β phase and a C14 type Laves phase in the investigated alloys. The mechanical properties such as yield strength, hardness and plastic strain for the investigated alloys are found to be significantly sensitive to volume fraction of the Laves phase. Ti-35Zr-5Fe shows impressive ultimate compressive strength (~1.7 GPa), yield strength (1138 MPa) and large plastic strain (23.2 %). The fracture mechanisms are dependent on the microstructure of the alloys. Additionally, the work-hardening ability of the investigated alloys have also been evaluated based on the analyses of slip band patterns formed around the micro-hardness indentations. Notably, the extreme brittleness is not encountered in all the Ti-35Zr-5Fe-xMn alloys and all exhibit very good compressive elongation including the maximum (32.5 %) in Ti-35Zr-5Fe.

Laves phase precipitation in Ti-Zr-Fe-Cr alloys with high strength and large plasticity

In this work, a novel serial of Ti-33Zr-xFe-yCr (x = 3, 5, 7 wt% and y = 2, 4 wt%) alloys was designed first with an expectation to obtain Laves phase in microstructure and then these alloys were produced using cold crucible levitation melting. Microstructure and phase analyses suggest the precipitation of a C15 type Laves phase with a dominating β phase in all the Ti-33Zr-xFe-yCr alloys except in Ti-33Zr-3Fe-2Cr alloy which has a single β phase microstructure. The volume fraction of the Laves phase increases upon increasing the Fe and Cr concentrations in Ti-Zr-Fe-Cr alloys. Mechanical properties evaluation reveals the highest ultimate compressive strength (~2 GPa) and superior plastic strain (33.6%) in Ti-33Zr-3Fe-4Cr alloy. Moreover, all the studied alloys exhibit extraordinarily high yield strength above 1 GPa and hardness exceeding 8 GPa. Embrittlement in Laves phase alloys, which is a common problem, is not encountered in this work as all the studied alloys display plastic strain including maximum elongation of 40%. The fracture behaviour of each studied alloy is also discussed in terms of the influence of Laves phase on a fracture, shear banding pattern and plastic deformation.

Correlation Between Microstructure and Corrosion Behavior of Zr-0.8Sn-1Nb-0.3Fe Alloy

Abstract Zr-0.8Sn-1Nb-0.3Fe zirconium alloy sheets were prepared by different heat treatment processes. Then OM and TEM were used to analyze the microstructure of the samples, and static autoclave tests were carried out in 360 °C/18.6 MPa/0.01 mol/L LiOH solution and 400 °C/10.3 MPa superheated steam to investigate the corrosion behavior. The results show that the second phase particles (SPPs) are mainly C14 type Zr(Nb, Fe)2 with a HCP structure, and the uniformity of SPPs distribution gradually becomes worse when the hot-rolling temperature increases from 600 to 700 °C. Aging treatment before hot-rolling not only improves the uniformity of SPPs distribution, but also promotes the diffusion of Nb, which increases the amount of βNb SPPs. Extension of final annealing time has little influence on size and distribution of the SPPs, but increases the Nb/Fe ratio in the SPPs. After long time corrosion tests, the corrosion resistance becomes worse when the hot-rolling temperature increases in both corrosion conditions. Aging treatment before hot-rolling can increase the corrosion resistance. Extension of final annealing time can also increase the corrosion resistance in LiOH solution, but decrease the corrosion resistance in superheated steam. The relationship between microstructure and corrosion resistance was discussed, and the size, distribution and the Nb content of SPPs are considered to be the main reason for the difference of the corrosion resistance of Zr-Sn-Nb-Fe zirconium alloys.

Alloy design, micromechanical and macromechanical properties of CoCrFeNiTax eutectic high entropy alloys

Based on binary phase diagrams and thermodynamic calculation, CoCrFeNiTax (x = 0.1, 0.3, 0.43, 0.5 and 0.7) eutectic high entropy alloys were designed. With increasing Ta content, as-cast microstructure changed from hypoeutectic (primary γ phase) to eutectic and to hypereutectic (primary Laves phase), and CoCrFeNiTa0.43 eutectic alloy was composed of γ phase with face-center cubic (FCC) structure and C14 type Laves phase with hexagonal close-packed (HCP) structure. Volume fraction of Laves phase increased with increasing Ta content, and thus microhardness was basically positive correlation with Ta content. Meanwhile, microhardness and elastic modulus of primary phase increased from primary γ phase to primary Laves phase, while hardness and elastic modulus of eutectic phases firstly decreased and then increased with increasing Ta content. In addition, based on nanoindentation load-displacement curves, the reverse analysis algorithms were used to obtain initial yield stress σy and strain hardening exponent n of primary γ phase and eutectic phases. Moreover, with increasing Ta content, the plasticity of CoCrFeNiTax alloys decreased, while the compression strength firstly increased and then decreased, and CoCrFeNiTa0.43 EHEA showed relatively high strength (2377 MPa) and relatively high plastic strain (17.5%).

Synthesis of a single phase of high-entropy Laves intermetallics in the Ti–Zr–V–Cr–Ni equiatomic alloy

The high-entropy Ti–Zr–V–Cr–Ni (20 at% each) alloy consisting of all five hydride-forming elements was successfully synthesised by the conventional melting and casting as well as by the melt-spinning technique. The as-cast alloy consists entirely of the micron size hexagonal Laves Phase of C14 type; whereas, the melt-spun ribbon exhibits the evolution of nanocrystalline Laves phase. There was no evidence of any amorphous or any other metastable phases in the present processing condition. This is the first report of synthesising a single phase of high-entropy complex intermetallic compound in the equiatomic quinary alloy system. The detailed characterisation by X-ray diffraction, scanning and transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the existence of a single-phase multi-component hexagonal C14-type Laves phase in all the as-cast, melt-spun and annealed alloys. The lattice parameter a = 5.08 Å and c = 8.41 Å was determined from the annealed material (annealing at 1173 K). The thermodynamic calculations following the Miedema’s approach support the stability of the high-entropy multi-component Laves phase compared to that of the solid solution or glassy phases. The high hardness value (8.92 GPa at 25 g load) has been observed in nanocrystalline high-entropy alloy ribbon without any cracking. It implies that high-yield strength (~3.00 GPa) and the reasonable fracture toughness can be achieved in this high-entropy material.

The Influence of the Valence Electron Concentration on the Structural Variation of the Laves Phases MgNi2–xGex

The influence of the partial substitution of Ni atoms by the similarly sized but electron‐richer Ge atoms with a similar electronegativity in the binary Laves phase MgNi2 is investigated. A small degree of substitution in MgNi2–xGex (x = 0.1) leads to the change of the hexagonal MgNi2‐type structure (C36) to the cubic C15 type, whereas higher amounts of Ge lead to the formation of the two new Laves phases Mg2Ni3Ge and MgNi1.30(5)Ge0.70, which were synthesized by the direct reaction of the elements in alumina and niobium crucibles using an induction furnace. The crystal structures of the two phases were determined by single‐crystal X‐ray diffraction. Mg2Ni3Ge (hR18‐MgNi2–xGex, x = 0.5) crystallizes in the Y2Rh3Ge‐type structure, which is an ordered variant of the cubic Laves phase MgCu2: space group R3m, a = 5.0300(7), c = 11.330(2) Å. hP36‐MgNi2–xGex with x = 0.70(6) crystallizes as a superstructure of the hexagonal Laves phase MgZn2: space group P63/mcm, a = 8.6946(2), c = 7.8127(3) Å. MgNi1.3Ge0.7 represents a new structure type. Gradual substitution of Ni by Ge in the Laves phase MgNi2 corresponds to an increase in the valence electron concentration (VEC) in the ternary phase system and leads to the series MgCu2 (C15 type), hR18‐Mg2Ni3Ge (superstructure of MgCu2 type), and hP36‐MgNi1.3Ge0.7 (superstructure of MgZn2 type). The electronic structures are discussed based on band structure calculations, and the results are compared to the pristine Laves phase MgNi2, MgCu2, and MgZn2 with VEC = 2/3, 4/3 and 2, respectively.

Magnetic and magnetocaloric properties of Er(Co1−xFex)2 intermetallic compounds

Structural, magnetic and magnetocaloric properties of Er(Co1−xFex)2 (x=0.0, 0.125 and 1) compounds are investigated. X-ray diffraction (XRD) analysis has revealed that the compounds crystallize in the C15 type Laves phase structure, with Fd-3m space group. All the samples are ferrimagnetically ordered, exhibiting a compensation point in the M(T) traces for x=1. The substitution of Fe to Co is accompanied by an increase of the Curie temperature from 42 to 591K, for x varying from 0 to 1. Magnetocaloric effect (MCE) is anticipated according to the Maxwell relation based on isothermal magnetization measurements. A maximum |ΔSM| value is found decreasing from 21J.kg−1.K−1for x=0 to 1.5J.kg−1.K−1 for x=1 under an applied magnetic field change of 0–5T. This decrease is accompanied by a change in the nature of the magnetic transition which becomes 2nd order when substituting Fe to Co.

High temperature deformation of Laves phase precipitates in alumina-forming austenitic stainless steels

Laves phases with the C14 type structure are present in recently-developed, alumina-forming austenitic (AFA) stainless steels. Here, for the first time, we show the Laves phase undergoes plastic deformation when such AFA steels are deformed at 700°C at strain rate of 5×10−4s−1. The gliding dislocations in the Laves phase leave behind stacking faults that we have analyzed using transmission electron microscopy. The stacking faults are on the basal plane of the Laves phase and are bounded by 1/3 〈101¯0〉 partial dislocations. These slip of dislocations are effective plastic deformation and improve the ductility of AFA materials.

MgCo2-D2 and MgCoNi-D2 systems synthesized at high pressures and interaction mechanism during the HDDR processing

MgCo2 and MgNiCo crystallize with hexagonal Laves type intermetallic structures of the C14 type and do not form hydrides at ambient hydrogen pressures. However, applying high hydrogen pressures in the GPa range forces the hydrogen absorption and leads to the formation of multi-phase compositions, which contain approximately 2.5 atoms H per formula unit of MgCo2 or MgNiCo and remain thermally stable under normal conditions.The hydrogenation of MgCo2 resulted in its decomposition to a ternary Mg2CoD5 deuteride and metallic cobalt. Phase-structural transformations accompanying the vacuum desorption of deuterium in the temperature range of 27–500°C were studied using in situ neutron powder diffraction. The investigation showed a complete recovery of the initial MgCo2 intermetallic via a Hydrogenation-Disproportionation-Desorption-Recombination process. At 300°C, the Mg2CoD5 deuteride first decomposed to elementary Mg and hexagonal Co. At 400°C, a MgCo phase was formed by interaction between Mg and Co. At the highest processing temperature of 500°C, a solid-state interaction of MgCo and Co resulted in the recovery of the initial MgCo2.The interaction of MgNiCo with deuterium under the synthesis conditions of 2.8GPa and 200°C proceeded in a more complex way. A very stable ternary deuteride MgNi2D3 was leached away while Co was separated in the form of Mg2CoD5 and the remaining nickel formed a solid solution with Co with the approximate composition Ni0.7Co0.3.The thermal desorption of deuterium from MgCo2D2.5 and from MgNiCoD2.5 has been studied by Thermal Desorption Spectroscopy with deuterium released into a closed volume. The observed effects nicely correlate with changes in the phase structural composition of the hydrides formed.MgCo2 is a new example of the hydrogen storage alloy, in which a successful HDDR processing results in the reversible formation of the initial intermetallic at much lower temperatures than in the equilibrium phase diagram of the Mg-Co system.

The formation and stacking faults of Fe and Cr containing Laves phase in Zircaloy-4 alloy

The crystallographic characterization and defect structure of precipitates plays a key role in the properties of Zr alloys. The precipitates in Zircaloy-4 alloy are studied in this work. The Zr-Fe-Cr particles are identified as the dominant precipitates at room temperature with C14 or C15 type Laves structure. The Fe/Cr ratio of C15 type Zr-Fe-Cr phase is slightly lower than that of C14 type phase. The {0001} stacking faults in C14 phase is observed and analyzed for the first time. Some new orientation relationships of C14 and C15 phases with α-Zr are identified.

Poisoning effect of oxygen on hydrogenation performance of a Zr-V-Ni Laves phase alloy

Zr-based Laves phase alloys have been considered as suitable getter materials for hydrogen isotopes recovery, storage and delivery and received considerable attention during past decades. This work focuses on hydrogenation performance of a pseudo-binary Zr-V-Ni Laves phase alloy with the composition of Zr(V0.95Ni0.05)2 after pre-exposure in different contents of O2. It is found that introduced pure oxygen can be rapidly absorbed by the fully activated Zr(V0.95Ni0.05)2 alloy within 40 s. All of the experimental samples pre-exposed in oxygen consist dominant C15 type ZrV2 Laves phase and minor Zr3V3O oxides. With the further increase the oxygen pressure to 4.0 kPa in specimen chamber, Bragg peaks of Zr2V, V-rich BCC solid solution phase and ZrO2 phase, including baddeleyite (α-ZrO2) with monoclinic structure and a small amount of tazheranite (γ-ZrO2) with cubic structure are observed in addition to the dominant ZrV2 and minor Zr3V3O phases. Meanwhile, it can be seen that the lattice parameter of cubic C15 type ZrV2 calculated from Rietveld refinement increases from 7.402 to 7.432 Å with the increase of O2 content and the corresponding unit cell volume increases 0.86 vol.% as the O2 pressure from 1.0 to 4.0 kPa, which indicates more oxygen atoms have been dissolved into the lattice of ZrV2. All of the oxygen poisoned Zr(V0.95Ni0.05)2 alloys can absorb hydrogen and the capacity decreases from 3.39 to 2.22 H A−1 with the increase of oxygen pressure from 1.0 to 4.0 kPa, comparing with the maximum hydrogen storage capacity (4.34 H A−1) of the fully activated fresh alloy. The existence of oxygen is found to decrease both capacity and kinetics of Zr(V0.95Ni0.05)2 by forming passivation layer oxides which block the dissociation of H2 molecule on the surface.

Effect of MWCNTs on hydrogen storage properties of a Zr-based Laves phase alloy

In this work, Zr(V0.95Ni0.05)2/MWCNTs composites were prepared by high energy ball-milling under the protection of Ar atmosphere starting with homogeneously annealed Zr(V0.95Ni0.05)2 alloy and MWCNTs. The results show that the as-milled Zr(V0.95Ni0.05)2 alloys with different concentration MWCNTs preserve a ZrV2 phase with C15 type structure and the lattice parameter of ZrV2 phase increases with increase of the MWCNTs concentration. During the hydrogenation process, it takes 35, 10, 14, 10 s to reach the 90% of their maximum hydrogen storage capacity at 773 K for the MWCNTs concentration is 1, 2, 5 and 10 wt.%, respectively. It is believed the addition of MWCNTs increase the hydrogenation kinetics in the way of the remarkably increased diffusion rate of H-atoms originating from MWCNTs with hollow structure. In addition, the activation property of Zr(V0.95Ni0.05)2 alloy is not affected significantly by the addition of MWCNTs. The slope of plateau decreases and the width of plateau increases with increasing MWCNTs concentration, which accounts for the increase of the reversible hydrogen storage capacity. In addition, the equilibrium pressure of Zr(V0.95Ni0.05)2 increases with the increase of MWCNTs concentration. The absolute value of enthalpy and entropy decrease as the MWCNTs concentration increase from 1 to 10 wt.%, indicating that the addition of MWCNTs dramatically decreases the stability of Zr(V0.95Ni0.05)2.

A New Theoretical Study of the Cr-Nb System

A new thermodynamic assessment of the binary Cr-Nb system was performed using the CALPHAD method based on a review of the available literature and ab initio calculations for the hypothetical end members of the C15 Laves phase. Recent experiments reported in the literature revealed that there is no C14 type high temperature phase in this system, which is in contrast to most of the literature. A thorough analysis of these reports, however, showed that the C14 phase has never been directly observed and that its presence had been derived from ternary phase diagram data, twinning of the C15 low temperature phase and erroneous interpretations of x-ray diffractograms. Due to the lack of clear evidence in favor of its existence, the C14 phase was not considered a thermodynamically stable compound in the present evaluation.

Can resistant coral-Symbiodinium associations enable coral communities to survive climate change? A study of a site exposed to long-term hot water input.

Climate change has led to a decline in the health of corals and coral reefs around the world. Studies have shown that, while some corals can cope with natural and anthropogenic stressors either through resistance mechanisms of coral hosts or through sustainable relationships with Symbiodinium clades or types, many coral species cannot. Here, we show that the corals present in a reef in southern Taiwan, and exposed to long-term elevated seawater temperatures due to the presence of a nuclear power plant outlet (NPP OL), are unique in terms of species and associated Symbiodinium types. At shallow depths (<3 m), eleven coral genera elsewhere in Kenting predominantly found with Symbiodinium types C1 and C3 (stress sensitive) were instead hosting Symbiodinium type D1a (stress tolerant) or a mixture of Symbiodinium type C1/C3/C21a/C15 and Symbiodinium type D1a. Of the 16 coral genera that dominate the local reefs, two that are apparently unable to associate with Symbiodinium type D1a are not present at NPP OL at depths of <3 m. Two other genera present at NPP OL and other locations host a specific type of Symbiodinium type C15. These data imply that coral assemblages may have the capacity to maintain their presence at the generic level against long-term disturbances such as elevated seawater temperatures by acclimatization through successful association with a stress-tolerant Symbiodinium over time. However, at the community level it comes at the cost of some coral genera being lost, suggesting that species unable to associate with a stress-tolerant Symbiodinium are likely to become extinct locally and unfavorable shifts in coral communities are likely to occur under the impact of climate change.

Large reversible magnetocaloric effect in RMn2 (R = Tb, Dy, Ho, Er) compounds

Magnetocaloric effect (MCE) of RMn2 (R=Tb, Dy, Ho, Er) compounds are investigated. TbMn2 and DyMn2 crystallize in cubic Laves phase structure (C15 type), whereas HoMn2 and ErMn2 crystallize in hexagonal Laves phase structure (C14 type). For TbMn2 compound, the field-induced metamagnetic transition accompanying a spontaneous cell volume expansion is observed (inverse MCE), which leads to a large positive value (8.3Jkg−1K−1) of magnetic entropy change around 36K under the field change of 0–1T, while the maximal values of magnetic entropy change (ΔSM) and the refrigerant capacity (RC) for other RMn2 (R=Dy, Ho, Er) compounds are −15.7, −18.4, −25.5Jkg−1K−1 and 403.6, 404.3, 316.0Jkg−1 around their TC with negligible thermal and magnetic hysteresis loss for the field change of 0–5T, respectively. The results suggest that RMn2 (R=Dy, Ho, Er) may be appropriate candidates for magnetic refrigerant working at low temperature region 10–80K.