Negative Thermal Expansion Operation-temperature Window Research Articles

Enhanced negative thermal expansion of boron-doped Fe43Mn28Ga28.97B0.03 alloy

Enhanced negative thermal expansion (NTE) properties are achieved by introducing a little amount of boron in the Fe43Mn28Ga28.97B0.03 alloy. As a result, this alloy shows a giant NTE coefficient of αl = −79.7 × 10−6 K−1 in a wide temperature range from 277 K to 136 K. Compared to the NTE characteristics in Fe43Mn28Ga29, the NTE operation temperature window has expanded by 74% with the corresponding coefficient of thermal expansion increased by 57% within the NTE temperature window for the boron-doped Fe43Mn28Ga28.97B0.03. In-situ synchrotron high-energy X-ray diffraction results suggest that by boron substitution, the large unit cell volume change across martensitic transformation and the wide phase transition temperature interval are responsible for the pronounced NTE behavior in Fe43Mn28Ga28.97B0.03. Moreover, for the Fe43Mn28Ga28.97B0.03 NTE material, the compressive strength and strain are significantly improved compared with that of Fe43Mn28Ga29. The present study indicates that Fe43Mn28Ga28.97B0.03 with enhanced NTE across martensitic transformation may be used for practical application as thermal-expansion compensators.

Negative thermal expansion in cubic and tetragonal structure coexisted La(Fe,Si)13hydride

In this research, the cubic and tetragonal crystal structure coexisted LaFe10.0Si3.0 compound and its hydride have been prepared by the arc-melting method and the novel electrolytic hydriding. Furthermore, the crystal structure, magneticand negative thermal expansion (NTE) properties of LaFe10.0Si3.0 and its hydride were investigated by the X-ray diffraction (XRD) and physical property measurement system (PPMS). Intriguingly, the NTE operation-temperature window of LaFe10.0Si3.0 has been broadened significantly after introducing interstitial hydrogen atoms. The further magnetic characterizations combined with theoretical analysis reveal that the increase of ferromagnetic to paramagnetic transition temperature due to stronger Fe-Fe magnetic exchange interactions contribute to the broad NTE operation-temperature window in the LaFe10.0Si3.0 hydride.

Broad Negative Thermal Expansion Operation-Temperature Window Achieved by Adjusting Fe-Fe Magnetic Exchange Coupling in La(Fe,Si)13 Compounds.

Cubic La(Fe,Si)13-based compounds have been recently developed as promising negative thermal expansion(NTE) materials, but the narrow NTE operation-temperature window(∼110 K) restricts their actual applications. In this work, we demonstrate that the NTE operation-temperature window of LaFe(13-x)Si(x) can be significantly broadened by adjusting Fe-Fe magnetic exchange coupling as x ranges from 2.8 to 3.1. In particular, the NTE operation-temperature window of LaFe10.1Si2.9 is extended to 220 K. More attractively, the coefficients of thermal expansion of LaFe10.0Si3.0 and LaFe9.9Si3.1 are homogeneous in the NTE operation-temperature range of about 200 K, which is much valuable for the stability of fabricating devices. The further experimental characterizations combined with first-principles studies reveal that the tetragonal phase is gradually introduced into the cubic phase as the Si content increases, hence modifies the Fe-Fe interatomic distance. The reduction of the overall Fe-Fe magnetic exchange interactions contributes to the broadness of NTE operation-temperature window for LaFe(13-x)Si(x).

Low-temperature negative thermal expansion behavior of LaFe11.2Al1.8−xSix compounds

The cubic NaZn13-type LaFe11.2Al1.8−xSix(x = 0.2, 0.3, 0.4 and 0.5) compounds with different Si content were fabricated by conventional arc-melting method, the structures of which were confirmed by powder X-ray diffraction (XRD) measurement at ambient temperature. Besides, the thermal expansion and magnetic properties of these samples were also researched by means of a strain gage and a physical property measurement system (PPMS). Significantly, it was found that the negative thermal expansion (NTE) behavior have been remarkably enhanced with substituting Al with Si atoms. Furthermore, the NTE operation-temperature window concurrently shifts toward a higher temperature region. The variable temperature XRD results indicate that LaFe11.2Al1.8−xSix retain cubic NaZn13-type structure when temperature varies from 20 K to 270 K, including the temperature region where NTE occurs. The further theoretical analysis combined with magnetic characterization reveal that the improvement of NTE behavior is attributed to the enhancement of Fe–Fe magnetic exchange interactions with doping Si atoms. It is noteworthy that this study displays a new pathway to improve the NTE property of La(Fe,Al)13-based compounds at low temperature region, which highlights the potential applications of NTE materials in cryogenic engineering.

Broad negative thermal expansion operation-temperature window in antiperovskite manganese nitride with small crystallites

Using spark plasma sintering (SPS), Mn3Cu0.6Ge0.4N crystallites have been fabricated with different crystallite sizes, and their magnetic properties and thermal behaviors were systemically investigated. With decreasing crystallite size, the magnetic transition becomes increasingly slow, accompanied by broadening of the negative thermal expansion (NTE) operation-temperature window. The NTE operation-temperature window for the 12-nm crystallite sample reaches at 140 K, which is about 75% larger than that of the 74-nm crystallite sample. The magnetic properties and NTE operation-temperature window can be tuned by varying the crystallite size. This discovery will promote an even wider range of practical applications in precision devices.

Broadened negative thermal expansion operation-temperature window in antiperovskite Mn3Zn0.6Ge0.4N prepared by spark plasma sintering

Anti-perovskite manganese nitrides Mn3Zn0.6Ge0.4N with different crystallite size were prepared by spark plasma sintering (SPS) at different sintering temperatures. Their negative thermal expansion (NTE) properties were investigated. It was found that the width of NTE operation-temperature window (ΔT) broadens with decreasing crystallite size. Typically, a broad ΔT of 105K was obtained in the compound Mn3Zn0.6Ge0.4N with average crystallite size of 54nm sintered at 700°C, of which the average linear thermal expansion coefficient was estimated to be −13.5×10−6K−1 in the NTE operation-temperature window. This antiperovskite manganese nitride Mn3Zn0.6Ge0.4N with broadened ΔT around room temperature is more useful for practical applications.

Giant Negative Thermal Expansion in NaZn13-Type La(Fe, Si, Co)13 Compounds

La(Fe, Si)13-based compounds are well-known magnetocaloric materials, which show a pronounced negative thermal expansion (NTE) around the Curie temperature but have not been considered as NTE materials for industrial applications. The NaZn13-type LaFe13-xSix and LaFe11.5-xCoxSi1.5 compounds were synthesized, and their linear NTE properties were investigated. By optimizing the chemical composition, the sharp volume change in La(Fe, Si)13-based compounds was successfully modified into continuous expansion. By increasing the amount of Co dopant in LaFe11.5-xCoxSi1.5, the NTE shifts toward a higher temperature region, and also the NTE operation-temperature window becomes broader. Typically, the linear NTE coefficient identified in the LaFe10.5Co1.0Si1.5 compound reaches as much as -26.1 × 10(-6) K(-1), with an operation-temperature window of 110 K from 240 to 350 K, which includes room temperature. Such control of the specific composition and the NTE properties of La(Fe, Si)13-based compounds suggests their potential application as NTE materials.

Negative thermal expansion and nearly zero temperature coefficient of resistivity in anti-perovskite manganese nitride Mn3CuN co-doped with Ag and Sn

Anti-perovskite manganese nitrides Mn3Cu0.6AgxSn0.4−xN (x=0–0.3) were synthesized by mechanical ball milling followed by solid state sintering. Their negative thermal expansion (NTE) coefficient and electrical resistivity were investigated in the temperature range of 80–300K. It is found that the transition temperature of NTE gradually moves toward lower temperature and the NTE operation-temperature window (ΔT) becomes narrower with increasing Ag content within the testing temperature ranges. Interestingly, though the electrical resistivity of the samples shows a metallic behavior, the variation of electrical resistivity appears to be nearly independent of temperature above the transition temperature of NTE. The present discovery highlights the potential application of NTE materials in cryogenic engineering.

REVIEW IN ANTIPEROVSKITE MANGANESE NITRIDES WITH NEGATIVE THERMAL EXPANSION PROPERTIES

Antiperovskite manganese nitrides are a group of negative thermal expansion (NTE) materials that have been developed rapidly in recent years. They exhibit important potential applica- tions due to isotropic NTE property, controllable coefficient of NTE and NTE operation temperature window, and good metallic and mechanical properties. In this review, state of the arts and recent development in the field of studying antiperovskite manganese nitrides have been summarized and commented, which consist of introduction of history, classification, preparation approaches, influencing factors and mechanisms of NTE for such materials. The prospects are also described for antiperovskite manganese nitrides.

Spin-glass behavior in the antiperovskite manganese nitride [formula omitted] codoped with Ge and Si

Antiperovskite manganese nitrides Mn 3 ( Cu 0.6 Si x Ge 0.4 − x ) N ( x = 0.05 , 0.1, 0.15) were prepared and their negative thermal expansion, magnetic and specific heat properties were investigated. A frozen state with a freezing temperature was found at ∼207 K in Mn 3 ( Cu 0.6 Si 0.15 Ge 0.25 ) N . This indicates that Mn 3 ( Cu 0.6 Si 0.15 Ge 0.25 ) N exhibits a spin glass state at low temperatures. We discussed the cause of spin glass behavior and correlated this spin glass behavior with broadening of the negative thermal expansion operation-temperature window of the manganese nitrides Mn 3 ( Cu 0.6 Si 0.15 Ge 0.25 ) N .

Low-temperature negative thermal expansion of the antiperovskite manganese nitride Mn3CuN codoped with Ge and Si

We have synthesized antiperovskite manganese nitrides Mn3(Cu0.6SixGe0.4−x)N, (x=0–0.2) and investigated their negative thermal expansion (NTE) in the temperature range of 80–300 K. We found that the transition temperature of NTE moves toward lower temperature region and as well the NTE operation-temperature window (ΔT) becomes broader with increasing Si content. Typically, the giant low-temperature NTE coefficient identified in Mn3(Cu0.6Si0.15Ge0.25)N reaches as large as −16×10−6 K−1, and its ΔT reaches as wide as 100 K. The magnetic properties of these compounds were measured and correlated with the broadened NTE operation-temperature window. The present discovery highlights the potential applications of NTE materials in cryogenic engineering.