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Materials Research

Print version ISSN 1516-1439On-line version ISSN 1980-5373

Mat. Res. vol.22  supl.1 São Carlos  2019  Epub Apr 11, 2019

http://dx.doi.org/10.1590/1980-5373-mr-2018-0647 

Articles

New Peritectoid Reaction Identified at the MnSb Alloy

Gerson Yoshinobu Iwamotoa  * 
http://orcid.org/0000-0002-4977-0087

Christiane de Arruda Rodriguesb 

Luciana Aparecida de Sousa Iwamotoc 

Rogerio de Almeida Vieiraa 

aLaboratório de Materiais e Manufatura Mecânica - LMMM, Universidade Federal de São Paulo - UNIFESP, Av. Manoel da Nóbrega, 1535, 09910720, Centro, Diadema, SP, Brasil

bLaboratório de Engenharia e Controle Ambiental (LENCA), Departamento de Engenharia Química, Universidade Federal de São Paulo - UNIFESP, Rua São Nicolau, 210, 09913-030, Centro, Diadema, SP, Brasil

cCentro de Terapia Celular e Molecular - CTCMOL, Universidade Federal de São Paulo - UNIFESP, São Paulo, SP, Brasil


ABSTRACT

The tunable Tc region of MnSb alloy (44 - 49 % at. Sb) was analyzed using OM, VSM, DSC, XRD, EDS and XRF characterization techniques. Thermal and magnetic analysis suggests the existence of a non reported irreversible reaction on heating, compatible to a reverse peritectoid transition MnxSb ➔ Mn2Sb + Mnx'Sb.

Keywords: Magnetic materials; phase transformation; MnSb metals and alloys; manganese-antimony alloys; Curie Temperature; perictetoid transformation

1. Introduction

The MnSb alloy presents an interesting phase, on atomic percentage of Sb (%at.Sb) from 45% to 48%, with Curie Temperature (Tc) varying from 90 °C to 314 °C. The composition limits of the MnSb phase and the corresponding Tc varies significantly at the reported phase diagrams (1-6), these divergences are summarized at Table 1. The minimum limit of the MnSb phase varies from 40.0 to 46.0 %at.Sb, and the maximum limit goes from 49.0 to 50.5 %at.Sb. Also the temperature of peritectic (from 840 to 853 °C) and eutectic (from 568 to 574 °C) reactions are reported at different temperatures. These divergences can be in part related to temperature range evaluated, presence of oxidation, melting and heat treatment methods, and/or chemical composition analysis method.

Table 1 MnSb's phase limits and temperature reactions 

Range (%atSb) Range Tc (°C) Peritectic Eutectic Temperature evaluation (°C)
Williams 40.0-50.0 ? - 328 853 573 100-1240
Teramoto 46.0-49.7 117-319 ? ? 400-900
Okamoto 45.0-49.0 90 - 314 840 570 0-940
Chen 45.5-50.0 ? 843 574 500-915
Vanyarkho 45.5-49.0 ? 841 568 400-920
Kainzbauer 45.5-50.5 ? 830 566 300-940

2. Materials and Method

Eight samples with atomic percentage of Sb (%atSb), from 43% to 50%, were prepared with high purity elements (Sb - Alfa Aesar 99.99% and Mn Alfa Aesar 99.98%), were weighed on precision equipment and melted, under argon atmosphere, at electric arc furnace (EAF). Each sample was melted 6 times, inverting its position after each melt. The ingots were annealed at 500°C for 5 days, slowly cooled (1°C min-1), named as "Rec", a part of the ingots were cut and annealed at 820 °C for 10 days and quenched and named as "TT". The ingots' chemical composition was checked at X-Ray Fluorescence (XRF) equipment, and the phases' stoichiometry at Scanning Electron Microscopy with Energy Dispersive Spectroscopy (EDS) equipment.

Also XRD (X-Ray Difractometer) with Rietveld method analysis, DSC (Differential Scanning Calorimeter), VSM (Vibratory Sample Magnetometer) and OM (Optical Microscope) equipments were used to characterize the samples.

3. Results and Discussion

The samples were identified in accord to its nominal composition, from "1 = 43% at Sb" to 8 = 50% at Sb, and respective heat treatment (TT or Rec). This study was focused on the region of "tunable" Curie Temperature, the partial phase diagram, Fig. 1., locates the quenched (TT) and annealed (Rec) samples analyzed in this study.

Figure 1 MnSb partial phase diagrams, from diverse authors, and the corresponding images, where: "a" = MnxSb phase, "b" = Mn2Sb phase, and "c" is predominantly Sb phase; Dark gray spots at TT_3 and TT_8 are holes caused at manipulation by fragility of material. 

Images obtained from OM, Fig. 1, evidenced a light gray phase named as "a" corresponding to MnxSb present on all samples, a dark phase (granular and stripes) named as "b" corresponding to Mn2Sb present on TT_2, TT_3 and Rec_2 samples, and an almost white phase named as "c" - predominantly Sb, present on TT_8 and Rec_8 samples. EDS analysis nominally confirmed the composition of the phases. The other micrographics' images show basically the same phases.

The reported Curie temperature (Tc) x stoichiometry, on known phase diagrams1-3, indicates higher Tc as the percentage of Sb increases. The measurement of composition at XRF and precision balance and their respective Tc do not converge to reported data, but do with EDS measures of the individual's phase, this can be explained by the first two are general measurements and the third is specific at MnSb phase. Giving evidences the Tc registered is exclusively related to MnxSb phase ("x" is the stoichiometry variation). The chemical composition of MnxSb measured at EDS, from 49.4% to 52.3 %at.Sb meaning "x" has a value between 1.02 and 0.91 (1.02>x>0.91) are not completely agreeing with phase diagrams1-3, where MnxSb varies from 45.5% to 50.0% at Sb (1.20>x>1.00). The samples Rec_1 and Rec_8 presents a secondary phase (Mn2Sb or Sb), meaning it exceeds the MnxSb phase limits. Extrapolating the data Tc x composition as a straight line from closer compositions, the range limit should be 49.5% at Sb for 90 °C, and 53.0 % at Sb for 316 °C, and "x" factor should vary from 0.883 to 1.020 on Rec samples. The Table 2 provides the collected data but is ordered in accord to "x" value of MnxSb phase, exclusively where it has only one phase (Rec_1 and Rec_2 presents two phases).

Table 2 chemical composition of samples (weighed and XRF) and EDS for MnxSb phase correlated to Tc. 

Sample Weighed (%atSb) XRF (%atSb) EDS - MnSb (%atSb) Tc (°C) MnxSb x =
Rec_1 43.1% 40.1% 48.9% 140.35 -
Rec_4 46.1% 48.1% 49.7% 102.06 1.013
Rec_2 44.1% 44.5% 50.5% 143.00 0.980
Rec_3 45.0% 47.1% 50.6% 177.22 0.977
Rec_5 47.1% 48.3% 51.2% 217.85 0.952
Rec_6 48.1% 48.7% 52.2% 246.04 0.915
Rec_7 49.1% 49.3% 53.1% 316.11 0.883
Rec_8 50.0% 52.8% 54.1% 316.90 -

The magnetic analysis (MxT) of TT and Rec samples, plotted at Fig. 2"a-e", evidenced hysteresis from heating/cooling curves, compatible to a reverse peritectoid reaction (MnxSb ➔ MnSb + Mn2Sb) on heating. When comparing the results to the Okamoto's phase diagram, the magnetic event: M1 is probably related to Mn2Sb's spin rotation (alignment with external magnetic field), M2 converges to variable Tc of MnxSb (0.883<x<1.013), M3 to Mn0.883Sb, and M4 is probably an AFM-FM (Anti-ferromagnetic - Ferromagnetic) reaction of Sb predominant phase (Mn0.05Sb0.95).

Figure 2 Magnetic analysis. a) TT_2; b) TT_3; c) TT_3; d) Rec_2; e) Rec_3; and f) Rec_8. 

Teramoto1 reported an irreversible reaction when analyzing a 46 %at.Sb quenched sample, after each measurement of five cicles, the susceptibility curve moved to upper temperatures, he attributed this behavior to the "precipitation of Mn2Sb phase from MnSb". Chen2 also mentioned the precipitation of Mn2Sb phase.

Only the sample Rec_8 didn't present this hysteresis, suggesting, at this stoichiometry and temperature range, probably the peritectoid transition does not occur anymore. On the other hand, the events M4 and M-4 were not expected. A similar event was reported by Nwodo3 as a FOMT (first order magnetic transition) AFM-FI (Anti-ferromagnetic ➔ Ferrimagnetic) reaction, attributed to a spin reorientation of Mn2Sb dopped with Sn (Mn2Sb0.9Sn0.1). At Rec_8 and TT_8 the present phases are "MnxSb + Sb", where "Sb" is apparently providing an AFM behavior to the alloy up to 256.69 °C on heating, when a FOMT occurs (event M4 - AFM ➔ FM), followed by an M3 event at 316.96 °C, a SOMT (second order magnetic transition) "FM ➔ PM" reaction (ferromagnetic ➔ paramagnetic).

The thermal analysis (DSC), Fig. 3, of Rec samples evidenced two endothermic peaks, the first identified as E1 from 65.98 to 79.77 °C, which is compatible to the reported precipitation of Mn2Sb from MnxSb, probably related to a crystaline structure change from MnxSb (hexagonal) to form Mn2Sb (tetragonal). And the second, E2, near 573 °C, compatible to a reverse peritectic reaction "MnxSb ➔ Mnx'Sb + Liquid", reported by Okamoto4 at 570 °C, and by Kainzbauer at 566 °C, but in disagreement with lower levels of Sb (Rec_3 to Rec_8), where it was expected to be near to 840 °C.

Figure 3 Heat flow x Temperature diagram - DSC data. 

The refinement of XRD data revealed 3 main phases "a = MnxSb (hexagonal-P63mmc)"; "b = Mn2Sb (tetragonal-P4nmm); "c = predominantly Sb (rhombohedral-R3m)". All the samples presented the "a" phase, while "b" was identified at Rec_1 and Rec_2, and from TT_1 to TT_6. The presence of "b" on samples TT_3 to TT_6 conflicts to published phase diagrams1,2,4-7, but agrees with the expected "precipitation" of Mn2Sb phase at high temperatures. The "c" phase is only present at TT_7, TT_8, Rec_7 and Rec_8. At Fig. 4, the "b" phase detected on sample TT_ 3 at the angles 25.82°, 27.33°, 34.11°, 41.93°, 44.51° and 62.43° reinforce the hypothesis of existence of the peritectoid reaction, as they were not detected at Rec_3 sample.

Figure 4 XRD Analysis, where 2 = 44%atSb, 3 = 45%atSb, 8 = 50%atSb on nominal stoichiometry. 

The volume of unit cells is larger as higher is the percentage of Sb (larger atomic ratio). The precipitation of Mn2Sb reduces the value of "x" due to the diffusion of Mn atoms on TT samples x Rec samples. The absence of Mn2Sb phase on Rec_8 and TT_8, and absence of Sb phase on Rec_3, TT_3, Rec_2 and TT_2 confirms they are out of the limits of respective solid solution. Details of parameters are plotted on the Table 3.

Table 3 cell's lattice parameters 

Cell's net parameters
Fase Parameter Rec_8 TT_8 Rec_3 TT_3 Rec_2 TT_2
MnxSb (P6) a (Å) 4.130 4.191 4.190 4.201 4.200 4.214
c (Å) 5.790 5.731 5.734 5.728 5.724 5.716
Volume 85.546 87.163 87.181 87.534 87.433 87.880
R-Bragg 4.331 3.036 4.379 3.997 3.324 3.242
X 1.00 1.00 1.09 1.00 1.22 1.09
Mn2Sb (P4) a (Å) 4.056 4.078 4.075 4.077
c (Å) 6.110 6.546 6.543 6.546
Volume 100.536 108.846 108.655 108.777
R-Bragg 1.584 1.770 2.519 2.620
Sb (R3) a (Å) 4.309 4.307
c (Å) 5.635 5.633
Volume 90.595 90.509
R-Bragg 1.399 2.350
GOF 1.83 1.88 1.68 1.89 1.49 1.45
RWP 8.74 7.68 14.71 7.42 12.24 5.67

4. Conclusions

The magnetic hysteresis between heating and cooling suggests a reaction with compositional change. The thermal analysis revealed two endothermic peaks E1 ~ 80 °C compatible to the Mn2Sb precipitation mentioned previously, and E2 ~ 573 °C on samples Rec_3 to Rec_8 samples agreeing to peritectic reaction at the limit border of Mn0.883Sb phase and "Mn0.883Sb + Sb" solid solution. The absence of E2 on samples Rec_1 and Rec_2, a two phase region of "Mn2Sb + MnxSb" is probably because at this stoichiometry there are no more exceeding Mn atoms to diffuse and permit the precipitation of Mn2Sb phase from MnSb.

The results suggests the existence of a reverse peritectoid reaction (MnxSb ➔ Mn2Sb + Mn0.883Sb) on heating at samples Rec_3 to Rec_6 (or more precisely 1.020≥x>0.883), also the existence of the two phase solid (Mn2Sb + MnxSb) at high temperature region (above E1 ~ 79 °C) from 33% to near 53 %at.Sb, but limited from 33% to 49.7 %at.Sb under this temperature.

5. Acknoledgements

Prof. Dr. Antonio D. Santos and prof. dr. Sergio A. Romero - DFMT/USP.

Prof. Dr. Fanny Béron, LMLT IF Gleb Wataghin, UNICAMP.

Prof. Dr. Davinson M. Silva and prof. dr. Silvano L. Santos, LPCM, FATEC.

6. References

1 Teramoto I, Van Run AMJG. The existence region and the magnetic and electrical properties of MnSb. Journal of Physics and Chemistry of Solids. 1968;29(2):347-355. DOI: 10.1016/0022-3697(68)90080-2 [ Links ]

2 Chen T. Growth of MnBi single crystals by pulling with a seed from nonstoichiometric molten solution. Journal of Crystal Growth. 1974;24-25:454-460. DOI: 10.1016/0022-0248(74)90357-1 [ Links ]

3 Nwodo AN, Kobayashi R, Wakamori T, Matsumoto Y, Mitsui Y, Hiroi M, et al. Quasi-First Order Magnetic Transition in Mn1.9Fe0.1Sb0.9Sn0.1. Materials Transactions. 2018;59(3):348-352. DOI: 10.2320/matertrans.M2017291 [ Links ]

4 Okamoto H. Manganese-Antimony Binary Phase Diagram. In: Massalski TB, ed. Binary Alloy Phase Diagrams. 2nd ed. Materials Park: ASM International; 1990. [ Links ]

5 Williams RS. Über die Legierungen des Antimons mit Mangan, Chrom, Silicium und Zinn; des Wismuts mit Chrom und Silicium und des Mangans mit Zinn und Blei. Zeitschrift für anorganische Chemie. 1907;55(1):1-33. DOI: 10.1002/zaac.19070550102 [ Links ]

6 Vanyarkho VG, Moshchalkova NA, Gunchenko VM, Fadeeva NV. On the existence of the compound MnSb. Inorganic Materials. 1988;24(6):762-765. [ Links ]

7 Kainzbauer P, Richter KW, Ipser H. Experimental Investigation of the Binary Mn-Sb Phase Diagram. Journal of Phase Equilibria and Diffusion. 2016;37(4):459-468. DOI: 10.1007/s11669-016-0470-2 [ Links ]

Received: October 02, 2018; Accepted: March 09, 2019

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