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Large room temperature relative cooling power in La0.5Pr0.2Ca0.1Sr0.2MnO3
Journal Pre-proof Large room temperature relative cooling power in La0.5Pr0.2Ca0.1Sr0.2MnO3 Ridha Skini, Sagar Ghorai, Petter Ström, Sergey Ivanov, Daniel Primetzhofer, Peter Svedlindh PII:
S0925-8388(20)30655-1
DOI:
https://doi.org/10.1016/j.jallcom.2020.154292
Reference:
JALCOM 154292
To appear in:
Journal of Alloys and Compounds
Received Date: 9 December 2019 Accepted Date: 10 February 2020
Please cite this article as: R. Skini, S. Ghorai, P. Ström, S. Ivanov, D. Primetzhofer, P. Svedlindh, Large room temperature relative cooling power in La0.5Pr0.2Ca0.1Sr0.2MnO3, Journal of Alloys and Compounds (2020), doi: https://doi.org/10.1016/j.jallcom.2020.154292. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
Large room temperature relative cooling power in La0.5Pr0.2Ca0.1Sr0.2MnO3 Ridha Skini 1,*, Sagar Ghorai 1, Petter Ström 2 , Sergey Ivanov 1,3, Daniel Primetzhofer 2, and Peter Svedlindh1 1 2
Engineering Sciences, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden
Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden 3
Karpov Institute of Physical Chemistry, RU-103064 K-64 Moscow, Russia
Abstract: The La0.5Pr0.2Ca0.1Sr0.2MnO3 compound has been investigated as a potential candidate for room temperature magnetocaloric refrigeration. The Rietveld refinement of X-ray powder diffraction patterns confirms that the compound crystalizes in an orthorhombic phase with the Pnma space group. Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis, verified the desired ratio of the elements in the compound. Using X-ray photoelectron spectroscopy two oxidation states of manganese (Mn), Mn4+ and Mn3+ were identified in the compound with relative amounts of 32% and 68%, respectively. The observed spin orbit splitting of the Mn-2p3/2 and Mn-2p1/2 levels was obtained as 11.7 eV. A ferromagnetic to paramagnetic transition was observed around 296 K, which makes the material interesting for magnetic cooling near room temperature. In addition, the absence of magnetic hysteresis provides another argument in favor of the studied compound. The isothermal entropy change (−∆
) and the relative cooling power (RCP) for a magnetic field
change of 5 T were found to be 4 J/kg K and 372 J/kg, respectively. From the comparison of the values of −∆
and RCP with those obtained for the archetypal magnetocaloric material
gadolinium, it is argued that our material can be considered as a potential candidate in cooling systems based on magnetic refrigeration.
Keywords: Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, room temperature, magnetic refrigeration.
*Corresponding author: Dr. Ridha Skini Telephone: +046 79 4324063 E-mail Adress: [email protected]
1.
Introduction
Heat transfer based on the magnetocaloric effect (MCE) is becoming a practical solution for the refrigerator, air conditioning and heat pump industries. It resolves the main issues affecting compressor-based systems by reducing energy consumption, cost of production and by eliminating the use of greenhouse gases [1]. For applications close to room temperature, gadolinium has been used as a prototypical magnetic refrigerant system due to its large MCE near room temperature. However, the high cost of this material, which can reach ~ 4000 $/kg, presents a real obstacle for large scale applications [2]. Recently, industrial prototypes based on materials with a “giant” MCE have been proposed [3]. These materials exhibit a first-order magnetic transition (FOMT) associated with a magnetostructural transition. Examples of these materials are Gd5(SixGe1-x)4 [1], La-Fe-Si-based [4], Mn-Fe-P-based [5] and NiMn-based Heusler alloys [6]. Common issues of these compounds are mainly the large thermal hysteresis (∆
) as well as the limited temperature span of the MCE making them less
suitable for applications [1,4–6]. Perovskite manganites with the general formula A1-xBxMnO3 (A = trivalent rare earth cation and B = divalent alkaline earth cation) have also been proposed as potential candidates for use in room temperature magnetic refrigeration due to their negligible ∆
. Generally, these materials present a second-order magnetic phase
transition (SOMT) and “conventional” MCE observed in a wide temperature range around the transition point, generally larger than that observed in case of FOMTs. Prominent examples are La2/3(Ca,Sr)1/3MnO3 and Pr0.63Sr0.37MnO3 [7,8]. The La0.7Ca0.1Sr0.2MnO3 compound crystallizes in a rhombohedral structure with the exhibits a magnetic entropy change (∆
3
space group [9]. The compound
)) over a broad temperature range with a relative
cooling power of 111 J/kg at 343 K for an applied magnetic field of 2.5 T [9]. Besides, it has been demonstrated that substituting small amounts of Pr for La on the perovskite A-site in La0.7Sr0.3MnO3 shifts the magnetic transition temperature ( ) toward lower temperatures accompanied by an enhancement of the MCE [10]. In this work, we have studied the effect of substituting La in La0.7Ca0.1Sr0.2MnO3 with the smaller sized Pr on the MCE as well as on the structural and magnetic properties. Interestingly, an enhancement of the MCE as well a shift of
toward room temperature were observed, making the proposed sample a promising
candidate for use as a room-temperature magnetic refrigerant.
2. Experimental details: The La0.5Pr0.2Ca0.1Sr0.2MnO3 (LPCSMO) compound was prepared by solid-state reaction starting from high purity oxides/carbonates; La2O3, Pr6O11, CaCO3, SrCO3 and MnO2. The mixture was calcined at 1473 K for 24 h with intermediate grindings. The temperature was slowly ramped at 5 K/min, and cooled down to room temperature at 2 K/min. The powder was then pressed into pellets and sintered at 1473 K. Finally, the sample was slowly cooled within the furnace at a rate of 2 K/ min under a flow of oxygen in order to keep the oxygen stoichiometry. The sample was characterized by X-ray powder diffraction (XRPD) at room temperature (295 K) using Cu-Kα radiation ( Bruker D8-advance diffractometer) by step scanning (0.013°) in the range of 10° ≤ 2 θ ≤140° with 12 second delay for each step. Elemental analysis of the sample was performed using energy dispersive X-ray fluorescence
(EDXRF) measurements, collected from a Pananalytical's Epsilon 3XLE spectrometer where a 50 kV, 3 mA rhodium anode X-ray tube was used. Rutherford backscattering spectrometry (RBS) with a 2 MeV 4He+ beam, and time-of-flight elastic recoil detection analysis (ToFERDA) with 36 MeV 127I8+ were performed on the polycrystalline LPCSMO. The beam was hitting the sample at normal incidence for RBS, and the energy detector was placed at a backscattering angle of 170°. In addition, a detector for particle induced X-ray emission (PIXE) was located at 135°. Further details on the PIXE detector are given elsewhere, for example in [11]. For ToF-ERDA the incidence angle was 23° ±1° ) with respect to the sample surface, and recoils were detected at 45° [12]. For oxidation state analysis, X-ray photoelectron spectroscopy (XPS) was used. The XPS spectra were recorded by using a “PHI Quantera II” system with an Al-Kα X-ray source and a hemispherical electron energy analyzer with a pass energy of 55.00eV. The magnetic measurements were performed in a Quantum Design MPMS in the temperature range from 390 K to 5 K with a maximum field of 5T.
3. Results and discussion 3.1. Structural properties The XRPD spectrum for the LPCSMO sample is shown in Fig. 1. The data were analyzed by the Rietveld method using the Fullprof program [13]. Three structural models, orthorhombic (Pnma), rhombohedral (R-3c) and monoclinic (P21/n) were tested and the best refinement including all the peak positions was obtained for the orthorhombic structure with Pnma space group. The obtained lattice parameters, Mn-O bond lengths and Mn-O-Mn bond angles of the sample are summarized in Table 1. A comparison with the literature shows that the parent sample La0.7Ca0.1Sr0.2MnO3 is indexed in a rhombohedric structure with R-3c space group [9]. Thus, isovalent substitution of the larger La3+ (
= 1.216 Å [14]) by the smaller Pr3+
(
= 1.179 Å [14]) in the LPCSMO sample leads to a local lattice distortion in the crystal
structure and a transition from rhombohedral to orthorhombic crystal structure. In order to confirm the structural phase, we have calculated the Goldschmidt tolerance factor (!" ) [15] defined as: !" = where
(, )
and
*
#
√& '
$
(1)
$)
are the ionic radii of A, B site and oxygen ions, respectively. For a typical
rhombohedral structure, the value of !" is 0.96 < !" < 1, while for an orthorhombic structure, the value of !" is <0.96 [16]. The calculated tolerance factor for LPCSMO using average values for the ionic radii of the A and B site ions was found to be 0.923, which confirms the orthorhombic
structure
for
our
sample.
Comparing
LPCSMO
with
its
parent
La0.7Ca0.1Sr0.2MnO3 compound, the transition from rhombohedral to orthorhombic structure plays an important role for the MCE, increasing the effective magnetic moment and decreasing
[9,17].
An extra phase of Mn3O4 was observed with 6.72 wt%. This phase is often detected in manganites due to the high temperature (> 1273 K) synthesis [18–21]. Mn3O4 is antiferromagnetic and its transition temperature is ~41 K, above this temperature it is paramagnetic [22]. Thus, the Mn3O4 phase will not have any significant effect on the measured magnetic properties of the main ferromagnetic orthorhombic phase with
= 296
K.
3.2. Ion Beam (IBA) and EDXRF Analyses: As a conventional method of IBA, RBS provides the possibility to identify the constituents of a material and determine their atomic fractions, commonly free from the need of standards, with sensitivity increasing with atomic number. ToF-ERDA provides complementary information where signals from different species are individually recorded for non-ambiguous
quantification. ToF-ERDA is particularly suitable for detection of light species down to hydrogen. A 2D energy-flight time histogram from ToF-ERDA performed on the investigated sample is shown in Fig. 2 and elements present at a concentration larger than ~0.5 at. % are indicated. The iodine signal seen in the figure originates from scattering of primary beam ions into the detector. From the ToF-ERDA data, depth profiling of each detected element was performed using Potku [23], and atomic fractions were generated from the integrals of the depth profiles between depths of 150 and 1500 units of 1015 at/cm2. In addition to the elements highlighted in Fig. 2, there was a faint H signal visible in the upper left corner of the energy-flight time histogram, which may originate from a small amount of water present on the sample surface due to transport and handling. Pr counts were treated as La here, as the signals are not distinguished. To calculate the (La+Pr) to Sr to Mn ratios as accurately as possible, the RBS data obtained from the sample was imported into SIMNRA [24] and compared to calculated spectra based on both the expected composition and that obtained through fitting the individual elemental fractions. The three clear steps seen in Fig. 3 correspond to signals from Mn, Sr and La+Pr, respectively, from left to right. La and Pr are again treated together as La, which yields a 2% error due to the different backscattering cross sections from La compared to Pr. The atomic composition of the LPCSMO sample, as measured by RBS and ToF-ERDA is reported in Table 2. We estimate that the result is acceptably close to the desired composition. In fact, the ratio ([La+Pr]/[Sr+Ca]) is measured as 1.99 (13), as compared to the expected 2.33, where the estimated error comes from propagating the individual errors from the elemental fractions to the ratio. The statistical uncertainty in the ratio of La+Pr to Mn determined by RBS is smaller than 1%. Thus, the 2% error due to the backscattering cross sections sets the limit on accuracy in this case. For Sr, the statistical variation in the La+Pr signal background yields an uncertainty of
2%. In conclusion, the La+Pr to Sr to Mn ratios reported here are accurate to within 2%. The oxygen fraction measured by ToF-ERDA is affected by several potential error sources, see for example [25], and can be expected to carry an error of approximately 10%. Finally, the smaller calcium fraction is more severely affected by background counts in the ToF-ERDA spectrum and we estimate a resulting error on the order of 20%. An estimation of the La to Pr ratio in the sample is made based on the PIXE data obtained in parallel to the RBS measurement. The recorded spectrum is shown in Fig. 4 with relevant peaks labelled by the element from which they originate and X-ray energy in keV. A spectrum from a sample without Pr is also included, scaled so that both have the same number of counts in the Lα peak from La at 4.65 keV. This peak is not overlapping with any signals from other elements for either spectrum. Around 5.0 keV the same Lα lines from Pr overlap with Lβ from La, forming a single peak. By subtracting the La signal in this peak using the data from the Pr-free sample, the signal from Pr Lα is obtained. Finally, the signal intensities from the respective Lα peaks are compared, showing a ratio of 0.32. This value is a rough estimate of the Pr to La ratio and can be compared to the desired ratio of 0.4. The analysis of the cationic composition of LPCSMO by using EDXRF is summarized in Table 2. Slightly higher values of the atomic percentage is observed for the trivalent A-site atoms, while slightly lower values of atomic percentage is observed for the divalent A-site cations, comparing with the expected composition. However, overall good agreement is observed comparing the cationic composition obtained from the EDXRF measurements with the expected composition.
3.3. X-ray Photoelectron Spectroscopy (XPS) The oxidation state of manganese (Mn) plays an important role in deciding the magnetic state of a Mn-based perovskite. For manganite materials, Mn can have three oxidation states; Mn2+,
Mn3+ and Mn4+. In order to determine the Mn oxidation state for LPCSMO, XPS measurements have been performed. In Fig. 5, the Mn-2p energy spectrum reveals due to spin-orbit splitting well separated 2p3/2 and 2p1/2 energy states [26]. These two energy states have contributions from the Mn3+ and Mn4+ ionic states, shown as pink and blue lines, respectively. The Mn3+/Mn4+ ratio was calculated as 2.13 (= 6.8/3.2), obtained from the area of the fitted curves in Fig.5, which is comparable to the expected ratio of 2.33. The Mn3+ and Mn4+ peaks were observed for 2p3/2 and 2p1/2 states at 641.36 eV, 643.14 eV, 652.82 eV and 654.28 eV, respectively. The observed spin-orbit splitting between 2p3/2 and 2p1/2 was calculated as 11.7 eV. From XRPD analysis, the extra Mn3O4 phase should contribute to the Mn2+ oxidation state. However, no significant contribution of a Mn2+ peak was observed in the XPS pattern, which can be related to the small percentage of the secondary phase.
3.4. Magnetic Properties Fig. 6 shows the temperature dependence of the field cooled magnetization using an applied magnetic field of 0.01 T. The experimental results show a Paramagnetic to Ferromagnetic (PM-FM) phase transition at the Curie temperature determined from the ,-⁄, vs. (inset Fig. 6). The value of
curve
was found to be 296 K. We note that 20 at% of Pr doping for
La in La0.7Ca0.1Sr0.2MnO3 shifts the magnetic transition from 343 K to 296 K which presents a main factor in room temperature cooling technology [9]. To better understand the magnetic behavior in the PM region, we have studied the temperature
dependence of the inverse magnetic susceptibility / 01
) (Fig. 6). In the PM region, /
) is
usually described by the Curie-Weiss law defined as,
χ=
C , T −θ p
(2)
where 2 is the Curie constant and
θ p is the Weiss temperature. The downturn of / 01 )
close to 34 is tentatively explained by the onset of short-range FM correlations above By fitting the high-temperature region of / 01 684 experimental effective magnetic moment 5677 (2 =
), we have determined 34 ; 9 # :'
<'
[27]. and the
& 5677 [27]); the values were found to
be 298 K and 5.289 μ) , respectively. According to the mean-field approximation, the > 6?
expected effective magnetic moment (5677
& ) for LaB.C PrB.& Ca&B.1 SrB.& MnB.J MnKB. O&0 can be
determined as: &
> 6?
& N = 0.2 × 5677 Pr
M5677
where 5677 Pr
> 6?
> 6?
(3)
) = 3.58 5) , 5677 Mn ) = 4.90 5) and 5677 MnK ) = 3.87 5) [28] .
The obtained value of 5677 5677
& & ) + 0.7 × 5677 Mn ) + 0.3 × 5677 MnK ),
is found to be equal to 4.8855) . The difference between
684 and 5677 can be considered as a typical characteristic of the Griffiths phase singularity
[27,28]. Fig. 7 shows the magnetic hysteresis loop of the sample recorded at 100 K. No hysteresis was detected varying the applied magnetic field from -2 to 2 T, which indicates negligible energy loss during the magnetization-demagnetization process. This point is highly desired for magnetic cooling applications [18] . The absence of hysteresis indicates that the transition is of second-order, in fact first-order magnetocaloric materials with giant magnetocaloric effect are generally accompanied by hysteretic losses which present a real obstacle for magnetocaloric applications [29]. Moreover, isothermal magnetization curves around the Curie temperature were recorded to evaluate the magnetocaloric effect in our material. The nature of the magnetic transition is checked using the Banerjee criterion, which is based on the Arrott plots (-& versus U/-) [30] . The positive slope of the isothermal magnetization curves shown in Fig. 8 are indicators of the second-order character of the phase transition.
Furthermore, we have calculated the magnetic entropy change from magnetization isotherms using Maxwell’s relationship defined as, [18,30] ∆
\
= 5B WB ^_` X
Y
[ ]U .
(4)
YZ \
Fig. 9 shows the temperature variation of the magnetic entropy change measured under applied magnetic fields up to 5T. The value of the isothermal entropy change increases with increasing magnetic field and achieves its highest values near room temperature. The maximum −∆
value was found to be 1.82 and 4 JKg-1K-1 under an applied magnetic field
of 2 and 5 T, respectively. In addition, a working temperature interval of ∼100 K was obtained, which enhances the temperature range of the heat transfer between the cold and hot sides and as a result improves the cooling efficiency. To take into consideration these points, we have calculated the relative cooling power (RCP) defined as [18]: 2b = ∆ where ∆
,d 8 ,d 8
×∆
ef\
,
(5)
is the maximum of the magnetic entropy change and ∆
at half maximum of ∆
). As expected, a significant value of
LPCSMO sample. The calculated
ef\
is the full width
2b was found for the
2b value is about 147 and 372 JKg-1 for an applied
magnetic field of 2 and 5T, respectively. These values are large compared to those obtained for La0.7Ca0.1Sr0.2MnO3 and some other manganite materials (Table 3). The enhancement of the 2b is primarily related to the effect of A-site ionic disorder, which broadens the peak of −∆ a
and therefore leads to the increase of the 2b [31]. Significantly, the material exhibits 2b about 90% of that of Gd, which is used as a benchmark material for magnetic
refrigerants at room temperature. The obtained results, such as the room temperature magnetic transition, the absence of magnetic hysteresis and the large MCE fulfill most criteria of magnetic refrigerants and confirm that the proposed material can be considered as a candidate for magnetic refrigeration at room temperature. However, additional measurements of the direct adiabatic temperature
change as well of the resistivity, thermal conductivity are necessary for a full evaluation of the magnetocaloric properties of our material.
Conclusions: The detailed chemical analysis by XRPD, EDXRF, XPS, RBS, PIXE and ToF-ERDA of LPCSMO, resulted in a complete and coherent description of the material used in this study. From XRPD analysis, a crystal structure change from rhombohedral to orthorhombic structure, helped to decrease the magnetic transition temperature and increase the effective magnetic moment compared to the parent La0.7Ca0.1Sr0.2MnO3 compound. From EDXRF, RBS and XPS analysis, a good agreement with the desired composition of the elements and desired Mn3+ and Mn4+ ratio was observed. The isothermal entropy change proved that the introduction of small amount of Pr in the parent La0.7Ca0.1Sr0.2MnO3 compound constitutes a successful attempt to shift the magnetic transition temperature close to room temperature. Along with an
2b comparable to that of the well-known gadolinium, and absence of
magnetic hysteresis make polycrystalline La0.5Pr0.2Ca0.1Sr0.2MnO3 a prominent candidate for room temperature magnetic refrigeration.
Acknowledgement: The Swedish Foundation for Strategic Research (SSF, contract EM-16-0039) supporting research on materials for energy applications is gratefully acknowledged. Infrastructural grants by VR-RFI (#2017-00646_9) and SSF (contract RIF14-0053) supporting accelerator operation are gratefully acknowledged. Support from the Russian Foundation for Basic Research (18-03-00245) is gratefully acknowledged. The authors are thankful to Vitalii Shtender for recording the XRPD data and to Daniel Hedlund for fruitful discussions and proofreading.
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34279. [31] S. Banik, I. Das, Effect of A-site ionic disorder on magnetocaloric properties in large band width manganite systems, J. Alloys Compd. 742 (2018) 248–255.
Table captions: Table 1: Lattice parameters and bond information from X-ray powder diffraction pattern. Table 2: Cationic fraction from EDXRF analysis and atomic fractions of elements from IBA of La0.5Pr0.2Ca0.1Sr0.2MnO3. In the results from IBA, the numbers for Ca and O come from ToF-ERDA, while the relative amounts of La+Pr, Sr and Mn are taken from the SIMNRA fit to the RBS data. Table 3: Summary of magnetocaloric properties of the La0.5Pr0.2Ca0.1Sr0.2MnO3 compound under a magnetic field of 2T compared with results reported for some other manganites in the literature.
Figure captions: Fig. 1: Rietveld refined XRPD pattern of the La0.5Pr0.2Ca0.1Sr0.2MnO3 compound. Upper/lower set of Bragg positions corresponds to main phase / Mn3O4 phase. Inset shows the comparison of orthorhombic and rhombohedral crystal structure fitting with the experimental XRPD data. Fig. 2: Raw ToF-ERDA data from La0.5Pr0.2Ca0.1Sr0.2MnO3. Fig. 3: RBS data with overlain SIMNRA calculated spectra for polycrystalline La0.5Pr0.2Ca0.1Sr0.2MnO3. The calculated spectra have been scaled to get the same number of counts as the experimental curve between 1310 and 1830 keV. Fig. 4: PIXE spectra recorded on La0.5Pr0.2Ca0.1Sr0.2MnO3 and La0.9Sr0.1MnO3 samples. Fig. 5: XPS data for the 2p state of Mn in La0.5Pr0.2Ca0.1Sr0.2MnO3. Fig. 6: Variation of the magnetization and inverse magnetic susceptibility (/ 01 = U ⁄-) vs. temperature at 5B U =0.01 T. Inset: plot of ,-⁄, as a function of temperature.
Fig. 7: Hysteresis loop of the La0.5Pr0.2Ca0.1Sr0.2MnO3 compound recorded at 300 K. Fig. 8: Arrott plots (-& versus U/-) around Fig. 9: Magnetic entropy change (−∆ 5 T.
with 5 K of temperature interval.
) vs. temperature under various magnetic fields up to
Table 1 La0.5Pr0.2Ca0.1Sr0.2MnO3 Orthorhombic (Pnma) = 5.46526(2) = 7.72285(3) = 5.50186(2) Mn-O1: 1.9597(6) Mn-O2: 1.9285(16) Mn-O1-Mn: 160.26(18) Mn-O2-Mn: 164.47(12) = 5.0, = 6.36, = 4.20
Compound Phase Lattice parameters (Å) Bond lengths (Å) Bond angles (ᵒ) Rietveld Refinement Parameters
Table 2 Elements
La Pr Ca Sr Mn O
Atomic percent (%) of cations from XRF Observed Expected 25.11(15) 25.00 10.50(8) 10.00 4.80(5) 5.00 9.40(7) 10.00 49.96(16) 50.00 -
Table 3
Atomic percent (%) from IBA Observed Expected 13.2(2) 14.0 (La+Pr) 2.2(4) 2.0 4.4(1) 4.0 21.0(4) 20.0 59(6) 60.0
Materials
(K)
−∆
,
(J kg-1 K-1)
References (J kg-1)
Gd
299
4.20
196
[1]
La0.8Ca0.2MnO3
236.5
2.23
112.36
[19]
La0.8K0.1
300
1.65
95.81
[30]
La0.7Ca0.1Sr0.2MnO3
343
2.1
83
[9]
La0.75Ca0.05Na0.2MnO3
300
3.12
90
[32]
La0.5Pr0.2Ca0.1Sr0.2MnO3 296
1.82
146.5
This work
0.1MnO3
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Highlights Chemical analysis by XRPD, EDXRF, XPS, RBS, PIXE and ToF-ERDA of polycrystalline La0.5Pr0.2Ca0.1Sr0.2MnO3 sample were investigated. - From XRPD analysis, a crystal structure change from rhombohedral to orthorhombic structure, helped to decrease the magnetic transition temperature and increase the effective magnetic moment compared to the parent La0.7Ca0.1Sr0.2MnO3 compound. - From EDXRF, RBS and XPS analysis, a good agreement with the desired composition of the elements and desired Mn3+ and Mn4+ ratio was observed. - The isothermal entropy change proved that the introduction of small amount of Pr in the parent La0.7Ca0.1Sr0.2MnO3 compound constitutes a successful attempt to shift the magnetic transition temperature close to room temperature. - Along with an
comparable to that of the well-known gadolinium, and absence of
magnetic hysteresis make polycrystalline La0.5Pr0.2Ca0.1Sr0.2MnO3 a prominent candidate for room temperature magnetic refrigeration. .
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S0925-8388(20)30655-1
DOI:
https://doi.org/10.1016/j.jallcom.2020.154292
Reference:
JALCOM 154292
To appear in:
Journal of Alloys and Compounds
Received Date: 9 December 2019 Accepted Date: 10 February 2020
Please cite this article as: R. Skini, S. Ghorai, P. Ström, S. Ivanov, D. Primetzhofer, P. Svedlindh, Large room temperature relative cooling power in La0.5Pr0.2Ca0.1Sr0.2MnO3, Journal of Alloys and Compounds (2020), doi: https://doi.org/10.1016/j.jallcom.2020.154292. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
Large room temperature relative cooling power in La0.5Pr0.2Ca0.1Sr0.2MnO3 Ridha Skini 1,*, Sagar Ghorai 1, Petter Ström 2 , Sergey Ivanov 1,3, Daniel Primetzhofer 2, and Peter Svedlindh1 1 2
Engineering Sciences, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden
Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden 3
Karpov Institute of Physical Chemistry, RU-103064 K-64 Moscow, Russia
Abstract: The La0.5Pr0.2Ca0.1Sr0.2MnO3 compound has been investigated as a potential candidate for room temperature magnetocaloric refrigeration. The Rietveld refinement of X-ray powder diffraction patterns confirms that the compound crystalizes in an orthorhombic phase with the Pnma space group. Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis, verified the desired ratio of the elements in the compound. Using X-ray photoelectron spectroscopy two oxidation states of manganese (Mn), Mn4+ and Mn3+ were identified in the compound with relative amounts of 32% and 68%, respectively. The observed spin orbit splitting of the Mn-2p3/2 and Mn-2p1/2 levels was obtained as 11.7 eV. A ferromagnetic to paramagnetic transition was observed around 296 K, which makes the material interesting for magnetic cooling near room temperature. In addition, the absence of magnetic hysteresis provides another argument in favor of the studied compound. The isothermal entropy change (−∆
) and the relative cooling power (RCP) for a magnetic field
change of 5 T were found to be 4 J/kg K and 372 J/kg, respectively. From the comparison of the values of −∆
and RCP with those obtained for the archetypal magnetocaloric material
gadolinium, it is argued that our material can be considered as a potential candidate in cooling systems based on magnetic refrigeration.
Keywords: Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, room temperature, magnetic refrigeration.
*Corresponding author: Dr. Ridha Skini Telephone: +046 79 4324063 E-mail Adress: [email protected]
1.
Introduction
Heat transfer based on the magnetocaloric effect (MCE) is becoming a practical solution for the refrigerator, air conditioning and heat pump industries. It resolves the main issues affecting compressor-based systems by reducing energy consumption, cost of production and by eliminating the use of greenhouse gases [1]. For applications close to room temperature, gadolinium has been used as a prototypical magnetic refrigerant system due to its large MCE near room temperature. However, the high cost of this material, which can reach ~ 4000 $/kg, presents a real obstacle for large scale applications [2]. Recently, industrial prototypes based on materials with a “giant” MCE have been proposed [3]. These materials exhibit a first-order magnetic transition (FOMT) associated with a magnetostructural transition. Examples of these materials are Gd5(SixGe1-x)4 [1], La-Fe-Si-based [4], Mn-Fe-P-based [5] and NiMn-based Heusler alloys [6]. Common issues of these compounds are mainly the large thermal hysteresis (∆
) as well as the limited temperature span of the MCE making them less
suitable for applications [1,4–6]. Perovskite manganites with the general formula A1-xBxMnO3 (A = trivalent rare earth cation and B = divalent alkaline earth cation) have also been proposed as potential candidates for use in room temperature magnetic refrigeration due to their negligible ∆
. Generally, these materials present a second-order magnetic phase
transition (SOMT) and “conventional” MCE observed in a wide temperature range around the transition point, generally larger than that observed in case of FOMTs. Prominent examples are La2/3(Ca,Sr)1/3MnO3 and Pr0.63Sr0.37MnO3 [7,8]. The La0.7Ca0.1Sr0.2MnO3 compound crystallizes in a rhombohedral structure with the exhibits a magnetic entropy change (∆
3
space group [9]. The compound
)) over a broad temperature range with a relative
cooling power of 111 J/kg at 343 K for an applied magnetic field of 2.5 T [9]. Besides, it has been demonstrated that substituting small amounts of Pr for La on the perovskite A-site in La0.7Sr0.3MnO3 shifts the magnetic transition temperature ( ) toward lower temperatures accompanied by an enhancement of the MCE [10]. In this work, we have studied the effect of substituting La in La0.7Ca0.1Sr0.2MnO3 with the smaller sized Pr on the MCE as well as on the structural and magnetic properties. Interestingly, an enhancement of the MCE as well a shift of
toward room temperature were observed, making the proposed sample a promising
candidate for use as a room-temperature magnetic refrigerant.
2. Experimental details: The La0.5Pr0.2Ca0.1Sr0.2MnO3 (LPCSMO) compound was prepared by solid-state reaction starting from high purity oxides/carbonates; La2O3, Pr6O11, CaCO3, SrCO3 and MnO2. The mixture was calcined at 1473 K for 24 h with intermediate grindings. The temperature was slowly ramped at 5 K/min, and cooled down to room temperature at 2 K/min. The powder was then pressed into pellets and sintered at 1473 K. Finally, the sample was slowly cooled within the furnace at a rate of 2 K/ min under a flow of oxygen in order to keep the oxygen stoichiometry. The sample was characterized by X-ray powder diffraction (XRPD) at room temperature (295 K) using Cu-Kα radiation ( Bruker D8-advance diffractometer) by step scanning (0.013°) in the range of 10° ≤ 2 θ ≤140° with 12 second delay for each step. Elemental analysis of the sample was performed using energy dispersive X-ray fluorescence
(EDXRF) measurements, collected from a Pananalytical's Epsilon 3XLE spectrometer where a 50 kV, 3 mA rhodium anode X-ray tube was used. Rutherford backscattering spectrometry (RBS) with a 2 MeV 4He+ beam, and time-of-flight elastic recoil detection analysis (ToFERDA) with 36 MeV 127I8+ were performed on the polycrystalline LPCSMO. The beam was hitting the sample at normal incidence for RBS, and the energy detector was placed at a backscattering angle of 170°. In addition, a detector for particle induced X-ray emission (PIXE) was located at 135°. Further details on the PIXE detector are given elsewhere, for example in [11]. For ToF-ERDA the incidence angle was 23° ±1° ) with respect to the sample surface, and recoils were detected at 45° [12]. For oxidation state analysis, X-ray photoelectron spectroscopy (XPS) was used. The XPS spectra were recorded by using a “PHI Quantera II” system with an Al-Kα X-ray source and a hemispherical electron energy analyzer with a pass energy of 55.00eV. The magnetic measurements were performed in a Quantum Design MPMS in the temperature range from 390 K to 5 K with a maximum field of 5T.
3. Results and discussion 3.1. Structural properties The XRPD spectrum for the LPCSMO sample is shown in Fig. 1. The data were analyzed by the Rietveld method using the Fullprof program [13]. Three structural models, orthorhombic (Pnma), rhombohedral (R-3c) and monoclinic (P21/n) were tested and the best refinement including all the peak positions was obtained for the orthorhombic structure with Pnma space group. The obtained lattice parameters, Mn-O bond lengths and Mn-O-Mn bond angles of the sample are summarized in Table 1. A comparison with the literature shows that the parent sample La0.7Ca0.1Sr0.2MnO3 is indexed in a rhombohedric structure with R-3c space group [9]. Thus, isovalent substitution of the larger La3+ (
= 1.216 Å [14]) by the smaller Pr3+
(
= 1.179 Å [14]) in the LPCSMO sample leads to a local lattice distortion in the crystal
structure and a transition from rhombohedral to orthorhombic crystal structure. In order to confirm the structural phase, we have calculated the Goldschmidt tolerance factor (!" ) [15] defined as: !" = where
(, )
and
*
#
√& '
$
(1)
$)
are the ionic radii of A, B site and oxygen ions, respectively. For a typical
rhombohedral structure, the value of !" is 0.96 < !" < 1, while for an orthorhombic structure, the value of !" is <0.96 [16]. The calculated tolerance factor for LPCSMO using average values for the ionic radii of the A and B site ions was found to be 0.923, which confirms the orthorhombic
structure
for
our
sample.
Comparing
LPCSMO
with
its
parent
La0.7Ca0.1Sr0.2MnO3 compound, the transition from rhombohedral to orthorhombic structure plays an important role for the MCE, increasing the effective magnetic moment and decreasing
[9,17].
An extra phase of Mn3O4 was observed with 6.72 wt%. This phase is often detected in manganites due to the high temperature (> 1273 K) synthesis [18–21]. Mn3O4 is antiferromagnetic and its transition temperature is ~41 K, above this temperature it is paramagnetic [22]. Thus, the Mn3O4 phase will not have any significant effect on the measured magnetic properties of the main ferromagnetic orthorhombic phase with
= 296
K.
3.2. Ion Beam (IBA) and EDXRF Analyses: As a conventional method of IBA, RBS provides the possibility to identify the constituents of a material and determine their atomic fractions, commonly free from the need of standards, with sensitivity increasing with atomic number. ToF-ERDA provides complementary information where signals from different species are individually recorded for non-ambiguous
quantification. ToF-ERDA is particularly suitable for detection of light species down to hydrogen. A 2D energy-flight time histogram from ToF-ERDA performed on the investigated sample is shown in Fig. 2 and elements present at a concentration larger than ~0.5 at. % are indicated. The iodine signal seen in the figure originates from scattering of primary beam ions into the detector. From the ToF-ERDA data, depth profiling of each detected element was performed using Potku [23], and atomic fractions were generated from the integrals of the depth profiles between depths of 150 and 1500 units of 1015 at/cm2. In addition to the elements highlighted in Fig. 2, there was a faint H signal visible in the upper left corner of the energy-flight time histogram, which may originate from a small amount of water present on the sample surface due to transport and handling. Pr counts were treated as La here, as the signals are not distinguished. To calculate the (La+Pr) to Sr to Mn ratios as accurately as possible, the RBS data obtained from the sample was imported into SIMNRA [24] and compared to calculated spectra based on both the expected composition and that obtained through fitting the individual elemental fractions. The three clear steps seen in Fig. 3 correspond to signals from Mn, Sr and La+Pr, respectively, from left to right. La and Pr are again treated together as La, which yields a 2% error due to the different backscattering cross sections from La compared to Pr. The atomic composition of the LPCSMO sample, as measured by RBS and ToF-ERDA is reported in Table 2. We estimate that the result is acceptably close to the desired composition. In fact, the ratio ([La+Pr]/[Sr+Ca]) is measured as 1.99 (13), as compared to the expected 2.33, where the estimated error comes from propagating the individual errors from the elemental fractions to the ratio. The statistical uncertainty in the ratio of La+Pr to Mn determined by RBS is smaller than 1%. Thus, the 2% error due to the backscattering cross sections sets the limit on accuracy in this case. For Sr, the statistical variation in the La+Pr signal background yields an uncertainty of
2%. In conclusion, the La+Pr to Sr to Mn ratios reported here are accurate to within 2%. The oxygen fraction measured by ToF-ERDA is affected by several potential error sources, see for example [25], and can be expected to carry an error of approximately 10%. Finally, the smaller calcium fraction is more severely affected by background counts in the ToF-ERDA spectrum and we estimate a resulting error on the order of 20%. An estimation of the La to Pr ratio in the sample is made based on the PIXE data obtained in parallel to the RBS measurement. The recorded spectrum is shown in Fig. 4 with relevant peaks labelled by the element from which they originate and X-ray energy in keV. A spectrum from a sample without Pr is also included, scaled so that both have the same number of counts in the Lα peak from La at 4.65 keV. This peak is not overlapping with any signals from other elements for either spectrum. Around 5.0 keV the same Lα lines from Pr overlap with Lβ from La, forming a single peak. By subtracting the La signal in this peak using the data from the Pr-free sample, the signal from Pr Lα is obtained. Finally, the signal intensities from the respective Lα peaks are compared, showing a ratio of 0.32. This value is a rough estimate of the Pr to La ratio and can be compared to the desired ratio of 0.4. The analysis of the cationic composition of LPCSMO by using EDXRF is summarized in Table 2. Slightly higher values of the atomic percentage is observed for the trivalent A-site atoms, while slightly lower values of atomic percentage is observed for the divalent A-site cations, comparing with the expected composition. However, overall good agreement is observed comparing the cationic composition obtained from the EDXRF measurements with the expected composition.
3.3. X-ray Photoelectron Spectroscopy (XPS) The oxidation state of manganese (Mn) plays an important role in deciding the magnetic state of a Mn-based perovskite. For manganite materials, Mn can have three oxidation states; Mn2+,
Mn3+ and Mn4+. In order to determine the Mn oxidation state for LPCSMO, XPS measurements have been performed. In Fig. 5, the Mn-2p energy spectrum reveals due to spin-orbit splitting well separated 2p3/2 and 2p1/2 energy states [26]. These two energy states have contributions from the Mn3+ and Mn4+ ionic states, shown as pink and blue lines, respectively. The Mn3+/Mn4+ ratio was calculated as 2.13 (= 6.8/3.2), obtained from the area of the fitted curves in Fig.5, which is comparable to the expected ratio of 2.33. The Mn3+ and Mn4+ peaks were observed for 2p3/2 and 2p1/2 states at 641.36 eV, 643.14 eV, 652.82 eV and 654.28 eV, respectively. The observed spin-orbit splitting between 2p3/2 and 2p1/2 was calculated as 11.7 eV. From XRPD analysis, the extra Mn3O4 phase should contribute to the Mn2+ oxidation state. However, no significant contribution of a Mn2+ peak was observed in the XPS pattern, which can be related to the small percentage of the secondary phase.
3.4. Magnetic Properties Fig. 6 shows the temperature dependence of the field cooled magnetization using an applied magnetic field of 0.01 T. The experimental results show a Paramagnetic to Ferromagnetic (PM-FM) phase transition at the Curie temperature determined from the ,-⁄, vs. (inset Fig. 6). The value of
curve
was found to be 296 K. We note that 20 at% of Pr doping for
La in La0.7Ca0.1Sr0.2MnO3 shifts the magnetic transition from 343 K to 296 K which presents a main factor in room temperature cooling technology [9]. To better understand the magnetic behavior in the PM region, we have studied the temperature
dependence of the inverse magnetic susceptibility / 01
) (Fig. 6). In the PM region, /
) is
usually described by the Curie-Weiss law defined as,
χ=
C , T −θ p
(2)
where 2 is the Curie constant and
θ p is the Weiss temperature. The downturn of / 01 )
close to 34 is tentatively explained by the onset of short-range FM correlations above By fitting the high-temperature region of / 01 684 experimental effective magnetic moment 5677 (2 =
), we have determined 34 ; 9 # :'
<'
[27]. and the
& 5677 [27]); the values were found to
be 298 K and 5.289 μ) , respectively. According to the mean-field approximation, the > 6?
expected effective magnetic moment (5677
& ) for LaB.C PrB.& Ca&B.1 SrB.& MnB.J MnKB. O&0 can be
determined as: &
> 6?
& N = 0.2 × 5677 Pr
M5677
where 5677 Pr
> 6?
> 6?
(3)
) = 3.58 5) , 5677 Mn ) = 4.90 5) and 5677 MnK ) = 3.87 5) [28] .
The obtained value of 5677 5677
& & ) + 0.7 × 5677 Mn ) + 0.3 × 5677 MnK ),
is found to be equal to 4.8855) . The difference between
684 and 5677 can be considered as a typical characteristic of the Griffiths phase singularity
[27,28]. Fig. 7 shows the magnetic hysteresis loop of the sample recorded at 100 K. No hysteresis was detected varying the applied magnetic field from -2 to 2 T, which indicates negligible energy loss during the magnetization-demagnetization process. This point is highly desired for magnetic cooling applications [18] . The absence of hysteresis indicates that the transition is of second-order, in fact first-order magnetocaloric materials with giant magnetocaloric effect are generally accompanied by hysteretic losses which present a real obstacle for magnetocaloric applications [29]. Moreover, isothermal magnetization curves around the Curie temperature were recorded to evaluate the magnetocaloric effect in our material. The nature of the magnetic transition is checked using the Banerjee criterion, which is based on the Arrott plots (-& versus U/-) [30] . The positive slope of the isothermal magnetization curves shown in Fig. 8 are indicators of the second-order character of the phase transition.
Furthermore, we have calculated the magnetic entropy change from magnetization isotherms using Maxwell’s relationship defined as, [18,30] ∆
\
= 5B WB ^_` X
Y
[ ]U .
(4)
YZ \
Fig. 9 shows the temperature variation of the magnetic entropy change measured under applied magnetic fields up to 5T. The value of the isothermal entropy change increases with increasing magnetic field and achieves its highest values near room temperature. The maximum −∆
value was found to be 1.82 and 4 JKg-1K-1 under an applied magnetic field
of 2 and 5 T, respectively. In addition, a working temperature interval of ∼100 K was obtained, which enhances the temperature range of the heat transfer between the cold and hot sides and as a result improves the cooling efficiency. To take into consideration these points, we have calculated the relative cooling power (RCP) defined as [18]: 2b = ∆ where ∆
,d 8 ,d 8
×∆
ef\
,
(5)
is the maximum of the magnetic entropy change and ∆
at half maximum of ∆
). As expected, a significant value of
LPCSMO sample. The calculated
ef\
is the full width
2b was found for the
2b value is about 147 and 372 JKg-1 for an applied
magnetic field of 2 and 5T, respectively. These values are large compared to those obtained for La0.7Ca0.1Sr0.2MnO3 and some other manganite materials (Table 3). The enhancement of the 2b is primarily related to the effect of A-site ionic disorder, which broadens the peak of −∆ a
and therefore leads to the increase of the 2b [31]. Significantly, the material exhibits 2b about 90% of that of Gd, which is used as a benchmark material for magnetic
refrigerants at room temperature. The obtained results, such as the room temperature magnetic transition, the absence of magnetic hysteresis and the large MCE fulfill most criteria of magnetic refrigerants and confirm that the proposed material can be considered as a candidate for magnetic refrigeration at room temperature. However, additional measurements of the direct adiabatic temperature
change as well of the resistivity, thermal conductivity are necessary for a full evaluation of the magnetocaloric properties of our material.
Conclusions: The detailed chemical analysis by XRPD, EDXRF, XPS, RBS, PIXE and ToF-ERDA of LPCSMO, resulted in a complete and coherent description of the material used in this study. From XRPD analysis, a crystal structure change from rhombohedral to orthorhombic structure, helped to decrease the magnetic transition temperature and increase the effective magnetic moment compared to the parent La0.7Ca0.1Sr0.2MnO3 compound. From EDXRF, RBS and XPS analysis, a good agreement with the desired composition of the elements and desired Mn3+ and Mn4+ ratio was observed. The isothermal entropy change proved that the introduction of small amount of Pr in the parent La0.7Ca0.1Sr0.2MnO3 compound constitutes a successful attempt to shift the magnetic transition temperature close to room temperature. Along with an
2b comparable to that of the well-known gadolinium, and absence of
magnetic hysteresis make polycrystalline La0.5Pr0.2Ca0.1Sr0.2MnO3 a prominent candidate for room temperature magnetic refrigeration.
Acknowledgement: The Swedish Foundation for Strategic Research (SSF, contract EM-16-0039) supporting research on materials for energy applications is gratefully acknowledged. Infrastructural grants by VR-RFI (#2017-00646_9) and SSF (contract RIF14-0053) supporting accelerator operation are gratefully acknowledged. Support from the Russian Foundation for Basic Research (18-03-00245) is gratefully acknowledged. The authors are thankful to Vitalii Shtender for recording the XRPD data and to Daniel Hedlund for fruitful discussions and proofreading.
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Table captions: Table 1: Lattice parameters and bond information from X-ray powder diffraction pattern. Table 2: Cationic fraction from EDXRF analysis and atomic fractions of elements from IBA of La0.5Pr0.2Ca0.1Sr0.2MnO3. In the results from IBA, the numbers for Ca and O come from ToF-ERDA, while the relative amounts of La+Pr, Sr and Mn are taken from the SIMNRA fit to the RBS data. Table 3: Summary of magnetocaloric properties of the La0.5Pr0.2Ca0.1Sr0.2MnO3 compound under a magnetic field of 2T compared with results reported for some other manganites in the literature.
Figure captions: Fig. 1: Rietveld refined XRPD pattern of the La0.5Pr0.2Ca0.1Sr0.2MnO3 compound. Upper/lower set of Bragg positions corresponds to main phase / Mn3O4 phase. Inset shows the comparison of orthorhombic and rhombohedral crystal structure fitting with the experimental XRPD data. Fig. 2: Raw ToF-ERDA data from La0.5Pr0.2Ca0.1Sr0.2MnO3. Fig. 3: RBS data with overlain SIMNRA calculated spectra for polycrystalline La0.5Pr0.2Ca0.1Sr0.2MnO3. The calculated spectra have been scaled to get the same number of counts as the experimental curve between 1310 and 1830 keV. Fig. 4: PIXE spectra recorded on La0.5Pr0.2Ca0.1Sr0.2MnO3 and La0.9Sr0.1MnO3 samples. Fig. 5: XPS data for the 2p state of Mn in La0.5Pr0.2Ca0.1Sr0.2MnO3. Fig. 6: Variation of the magnetization and inverse magnetic susceptibility (/ 01 = U ⁄-) vs. temperature at 5B U =0.01 T. Inset: plot of ,-⁄, as a function of temperature.
Fig. 7: Hysteresis loop of the La0.5Pr0.2Ca0.1Sr0.2MnO3 compound recorded at 300 K. Fig. 8: Arrott plots (-& versus U/-) around Fig. 9: Magnetic entropy change (−∆ 5 T.
with 5 K of temperature interval.
) vs. temperature under various magnetic fields up to
Table 1 La0.5Pr0.2Ca0.1Sr0.2MnO3 Orthorhombic (Pnma) = 5.46526(2) = 7.72285(3) = 5.50186(2) Mn-O1: 1.9597(6) Mn-O2: 1.9285(16) Mn-O1-Mn: 160.26(18) Mn-O2-Mn: 164.47(12) = 5.0, = 6.36, = 4.20
Compound Phase Lattice parameters (Å) Bond lengths (Å) Bond angles (ᵒ) Rietveld Refinement Parameters
Table 2 Elements
La Pr Ca Sr Mn O
Atomic percent (%) of cations from XRF Observed Expected 25.11(15) 25.00 10.50(8) 10.00 4.80(5) 5.00 9.40(7) 10.00 49.96(16) 50.00 -
Table 3
Atomic percent (%) from IBA Observed Expected 13.2(2) 14.0 (La+Pr) 2.2(4) 2.0 4.4(1) 4.0 21.0(4) 20.0 59(6) 60.0
Materials
(K)
−∆
,
(J kg-1 K-1)
References (J kg-1)
Gd
299
4.20
196
[1]
La0.8Ca0.2MnO3
236.5
2.23
112.36
[19]
La0.8K0.1
300
1.65
95.81
[30]
La0.7Ca0.1Sr0.2MnO3
343
2.1
83
[9]
La0.75Ca0.05Na0.2MnO3
300
3.12
90
[32]
La0.5Pr0.2Ca0.1Sr0.2MnO3 296
1.82
146.5
This work
0.1MnO3
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Highlights Chemical analysis by XRPD, EDXRF, XPS, RBS, PIXE and ToF-ERDA of polycrystalline La0.5Pr0.2Ca0.1Sr0.2MnO3 sample were investigated. - From XRPD analysis, a crystal structure change from rhombohedral to orthorhombic structure, helped to decrease the magnetic transition temperature and increase the effective magnetic moment compared to the parent La0.7Ca0.1Sr0.2MnO3 compound. - From EDXRF, RBS and XPS analysis, a good agreement with the desired composition of the elements and desired Mn3+ and Mn4+ ratio was observed. - The isothermal entropy change proved that the introduction of small amount of Pr in the parent La0.7Ca0.1Sr0.2MnO3 compound constitutes a successful attempt to shift the magnetic transition temperature close to room temperature. - Along with an
comparable to that of the well-known gadolinium, and absence of
magnetic hysteresis make polycrystalline La0.5Pr0.2Ca0.1Sr0.2MnO3 a prominent candidate for room temperature magnetic refrigeration. .
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: