Abstract
The crystal structure, cryogenic magnetic properties, and magnetocaloric performance of double perovskite Eu
2
NiMnO
6
(ENMO), Gd
2
NiMnO
6
(GNMO), and Tb
2
NiMnO
6
(TNMO) ceramic powder ...samples synthesized by solid-state method have been investigated. X-ray diffraction structural investigation reveal that all compounds crystallize in the monoclinic structure with a P2
1
/n space group. A ferromagnetic to paramagnetic (FM-PM) second-order phase transition occurred in ENMO, GNMO, and TNMO at 143, 130, and 112 K, respectively. Maximum magnetic entropy changes and relative cooling power with a 5 T applied magnetic field are determined to be 3.2, 3.8, 3.5 J/kgK and 150, 182, 176 J/kg for the investigated samples, respectively. The change in structural, magnetic, and magnetocaloric effect attributed to the superexchange mechanism of Ni
2+
–O–Mn
3+
and Ni
2+
–O–Mn
4+
. The various atomic sizes of Eu, Gd, and Tb affect the ratio of Mn
4+
/Mn
3+
, which is responsible for the considerable change in properties of double perovskite.
•Ho2MMnO6 (M = Fe, Co, and Ni) synthesized by soli-state reaction.•Curie temperatures changes with different B-site elements in double perovskite.•All samples undergo second order phase ...transition.•Structural and magnetic properties change with 3d-transition element in DPs.•Magnetic entropy change is found as 10.2, 3.4 and 4.7 J/kgK at ΔH = 7 T.
We report our systematic investigation of structural, magnetic, and magnetocaloric properties of double perovskite compounds Ho2FeMnO6, Ho2CoMnO6, and Ho2NiMnO6, which crystallize into monoclinic crystal structure with P21/n space group. The magnetic phase transition temperatures are determined to be 7.5 K for Ho2FeMnO6, 69 K for Ho2CoMnO6, and 71.5 K for Ho2NiMnO6, where Ho2FeMnO6 exhibits an antiferromagnetic to paramagnetic phase transition, while Ho2CoMnO6 and Ho2NiMnO6 exhibits ferromagnetic to paramagnetic phase transitions. The magnetic entropy change (−ΔSM), which are found to be 10.2, 3.4 and 4.7 J/kgK at ΔH = 7 T for Ho2FeMnO6, Ho2CoMnO6, and Ho2NiMnO6 samples, respectively. The magnetic and magnetocaloric characteristics of double perovskite compounds are well explained based on structural and electronic properties. For future applications, our quantitative method provides a guideline for magnetic property engineering of double perovskite systems containing ferromagnetic 3d transition metals.
Abstract
We report the effect of Ni-doped ZnO thin films on the photodegradation of methylene blue (MB) under visible irradiation. The Ni-doped ZnO thin films were deposited on a silicon substrate by ...ultrasonic spray pyrolysis (USP) at 450 °C for 15 minutes. The ZnO thin films are characterized by X-ray diffraction (XRD) and UV-Vis spectroscopy. The X-ray diffraction (XRD) pattern for all samples confirms that the crystalline phase of Ni-doped ZnO thin films is polycrystalline hexagonal wurtzite. However, due to the Ni incorporation into the ZnO site, there is a change in the crystal plane. All ZnO films confirmed photocatalytic properties, indicating methylene blue (MB) degradation under visible irradiation. Nevertheless, the degradation of the MB dye increased by about 76% with increasing Ni incorporation. Therefore, we confirmed that Ni incorporation affects the photocatalytic properties of the ZnO thin films.
Rare-earth double perovskite oxides have intriguing magnetocaloric properties at cryogenic temperatures. In this study, Ho2NiMnO6 and Ho2CoMnO6 were synthesized using the sol–gel method, which ...crystallized in a monoclinic structure in the P21/n space group. The magnetic phase transition was observed at 81.2 K for Ho2NiMnO6 and 73.5 K for Ho2CoMnO6. The presence of a paramagnetic matrix and short-range ferromagnetic clusters causes magnetic disorder in these double perovskites, resulting in Griffiths phase formation. The Arrott plot confirms that compounds undergo second-order phase transition. At an applied magnetic field of 5 T, the maximum magnetic entropy change (−ΔS) for the studied compounds is 1.7 and 2.2 J kg−1 K−1, respectively. The transition metals Ni and Co in a double perovskite cause lattice distortion in the structural parameters and oxidation states of manganese (Mn3+/Mn4+), which changes the magnetic and magnetocaloric properties. The quantitative approach provides a systematic study of magnetocaloric properties of the rare earth double perovskite compounds with ferromagnetic 3d transition elements.
Rare-earth double perovskite oxides have intriguing magnetocaloric properties at cryogenic temperatures. In this study, Ho
NiMnO
and Ho
CoMnO
were synthesized using the sol-gel method, which ...crystallized in a monoclinic structure in the
2
/
space group. The magnetic phase transition was observed at 81.2 K for Ho
NiMnO
and 73.5 K for Ho
CoMnO
. The presence of a paramagnetic matrix and short-range ferromagnetic clusters causes magnetic disorder in these double perovskites, resulting in Griffiths phase formation. The Arrott plot confirms that compounds undergo second-order phase transition. At an applied magnetic field of 5 T, the maximum magnetic entropy change (-Δ
) for the studied compounds is 1.7 and 2.2 J kg
K
, respectively. The transition metals Ni and Co in a double perovskite cause lattice distortion in the structural parameters and oxidation states of manganese (Mn
/Mn
), which changes the magnetic and magnetocaloric properties. The quantitative approach provides a systematic study of magnetocaloric properties of the rare earth double perovskite compounds with ferromagnetic 3d transition elements.
The structural, magnetic, and magnetocaloric properties of Ho
1−
x
Ca
x
MnO
3
(
x
= 0, 0.1, 0.2, and 0.3) manganites were investigated in depth in this work. The samples were made by using standard ...solid-state reaction. The calcium-doped samples are formed in orthorhombic crystal structure with Pnma space group, while undoped sample shows hexagonal crystal structure with P63cm space group according to room temperature XRD measurements and Rietveld refinement by using the TOPAS software. The field emission scanning electron microscopy (FESEM) was used to examine the microstructure, and an energy-dispersive X-ray diffractometer (EDX) was used to estimate chemical compositions. At the Curie temperature, all the samples show a second-order magnetic phase transition. It has been discovered that when the amount of calcium doping increases, the Curie temperature increases. The effective magnetic moments (μ
eff
) of HoMnO
3
, Ho
0.9
Ca
0.1
MnO
3
, Ho
0.8
Ca
0.2
MnO
3
, and Ho
0.7
Ca
0.3
MnO
3
are 10.71, 10.93, 11.17, and 11.54 μB, respectively, which are equivalent to the theoretical value of 11.45 μB. The magnetic entropy change (− ΔS
M
) was calculated by using isothermal magnetization versus applied magnetic field. The calculated − ΔS
M
= 8.9 Jkg
−1
K
−1
value for undoped HoMnO
3
sample at 17.7 K, while with an increase in calcium doping, the − ΔS
M
value have been drop down from 3.3 to 2.2 Jkg
−1
K
−1
about 35 K temperature.
Electron-doped superconductor Eu1.85Ce0.15CuO4+α-δ has been synthesized using solid state reaction method. The purpose of this research is to study the effect of heating process with and without ...annealing treatment to its superconductivity. The sample without annealing treatment was covered by CuO to prevent the excess of oxygen in sample during heating process. All samples were characterized by XRD, resistivity and susceptibility measurement to study structure, electrical and magnetic properties of Eu1.85Ce0.15CuO4+α-δ samples with different heating process. From XRD measurement, it is found that all samples have tetragonal crystal with T' structure. From magnetic susceptibility and resistivity measurement, superconductivity was observed only in the sample with annealing treatment. The absence of superconductivity in sample without annealing was probably due to the existence of excess oxygen.
Research related to the provision of magnetic field strength in the flow of fuel that can cause more complete combustion has been reported by many researchers and most of these observations were ...carried out by measuring machine performance using a dynamometer. Given the dynamometer prices are very expensive then another way to prove the occurrence of complete combustion is through the combustion chamber indicator. The hypothesis is the greater magnetic field passed by fuel, the more perfect the combustion is. In addition, the combustion chamber temperature also increases and thermal efficiency increases. The fuel used is biodiesel derived from cooking oil waste, biodiesel 100% (denoted as B0), a blend of biodiesel (20%)-diesel (80%) (denoted as B20), a blend of biodiesel (40%)-diesel (60%) (denoted as B40), a blend of biodiesel (30%)-diesel (30%) (denoted as B70), and diesel 100% (denoted as B100). The magnetic field used is 500 Gauss, 900 Gauss and 1500 Gauss. Measurement of combustion temperature is using R type temperature sensor, which is connected to the NI USB interface to computer and LabVIEW for data acquisition. 13 HP capacity of diesel engine was used. The results obtained is 13 % temperature increase in the combustion chamber of the engine and 7 - 12% thermal efficiency increase equipped with a magnet compared to a non-magnetic engine.
Research on synthesis of Li4Ti5O12 has been carried out using ultrasonic method with the objective to study the influence of the Sn addition to the materials conductivity and structure of lithium ...titanate. The starting materials used were LiOH and TiO2, while Sn was used as an additive with percentages of 0, 5%, 10%, 15% and 20%. Lithium hydroxide, titanium dioxide, and Sn were mixed into an aquabidest media and stirred for two hours at a rate of 300 rpm. Then it was reacted with the help of ultrasound for two hours, filtered and washed with distilled water and then rinsed with acetone. After drying overnight at room temperature, the resulting powder material is compacted using a hydraulic press at a pressure of 4000 psi and the obtained pellets were sintered in the furnace at 800 °C for two hours. Characterization was performed using LCR meter and X-ray diffraction (XRD) to measure the conductivity and the crystal structure, respectively. The SEM-EDS are used to observe the morphology and the composition of the material. The results of the Rietveld analysis showed that the un-doped sample correspond to cubic crystal structure with space group of Fd-3m that belong to Li4Ti5O12 and monoclinic crystal structure with space group of C12/c1 that belong to Li2TiO3. It turned out that the increase of Sn; did not change in the ratio between Li4Ti5O12 and Li2TiO3, as well as in the lattices constant for all three phases. The optimum conductivity of 6.57 × 10−6 S/cm was obtained for 5 % Sn addition to Li4Ti5O12. A more homogeneous particle distribution was observed by SEM, due to ultrasonic method. It is concluded that the Sn addition to Li4Ti5O12 has improved structural and electrical performance of the anode materials for lithium ion battery.
Abstract
This study aims to make a catalyst from biomass waste in the form of coconut coir and apply it to the transesterification process of cocodiesel. The raw material for cocodiesel in this study ...was a coconut-based cooking oil that was also a waste and could pollute the environment. The research method includes cooking oil analysis, the catalyst’s preparation, and the catalyst’s characterization with Brunauer-Emmet-Teller (BET), X-ray fluorescence (XRF), X-ray diffraction (XRD), and Scanning electron microscope (SEM) analysis. The next step was the application of the catalyst in the transesterification reaction. The results showed interesting information, in which the addition of the calcination process increased the catalyst’s surface area and crystallinity ratio. Applying a catalyst in converting used cooking oil to cocodiesel gave 48.5% and 51% yields with densities close to the biodiesel standard.
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