In this paper,we report on the crystal structure and magnetic properties of the nano structured Baordered phases of rare-earth manganites obtained from the optimally doped solid solutions Ln0.70Ba0.30MnO3(Ln=Pr,Nd).Th...In this paper,we report on the crystal structure and magnetic properties of the nano structured Baordered phases of rare-earth manganites obtained from the optimally doped solid solutions Ln0.70Ba0.30MnO3(Ln=Pr,Nd).The materials were studied by X-ray diffraction,scanning electron microscopy,energy dispersive spectroscopy and SQUID-magnetometry techniques.It is found that states with different degrees of cation ordering in the A-sublattice of the ABO3 perovskite can be obtained by employing special conditions of chemical treatment.In particular,reduction of the parent compounds results in the formation of a nanocomposite containing ferrimagnetic anion-deficient ordered phase LnBaMn2O5.Oxidation of the composite does not change an average size of the nanocrystallites,but drastically alters their phase composition to stabilize ferromagnetic stoichiometric ordered phase LnBaMn2O6 and ferromagnetic superstoichiometric disordered phase Ln0.90Ba0.10MnO3+δ.It is shown that the magnetic properties of the materials are determined by the joint action of chemical(cation ordering)and external(surface tension)pressures.展开更多
We construct a Landau-Ginzburg thermodynamic potential,and the corresponding phase diagram for pristine and slightly doped bismuth ferrite,a ferroelectric antiferromagnet at room temperature.The potential is developed...We construct a Landau-Ginzburg thermodynamic potential,and the corresponding phase diagram for pristine and slightly doped bismuth ferrite,a ferroelectric antiferromagnet at room temperature.The potential is developed based on new X-ray and neutron diffraction experiments complementing available data.We demonstrate that a strong biquadratic antiferrodistortive-type coupling is the key to a quantitative description of Bi_(1−x)La_(x)FeO_(3) multiferroic phase diagram including the temperature stability of the antiferromagnetic,ferroelectric,and antiferrodistortive phases,as well as for the prediction of novel intermediate structural phases.Furthermore,we show that“rotomagnetic”antiferrodistortive-antiferromagnetic coupling is very important to describe the ferroelectric polarization and antiferrodistortive tilt behavior in the R3c phase of BiFeO_(3).The Landau-Ginzburg thermodynamic potential is able to describe the sequence of serial and trigger-type phase transitions,the temperature-dependent behavior of the order parameters,and the corresponding susceptibilities to external stimuli.It can also be employed to predict the corresponding ferroelectric and antiferrodistortive properties of Bi_(1−x)La_(x)FeO_(3) thin films and nanoparticles by incorporating the gradient and surface energy terms that are strongly dependent on the shape,size,and preparation method.展开更多
In this research paper,we utilized the traditional high-temperature solid-state reaction method to fabricate the K_(0.495)Na_(0.520)NbO_(3),K_(0.480)Na_(0.535)NbO_(3)and K_(0.475)Na_(0.540)NbO_(3)(abbreviated as KNN-1...In this research paper,we utilized the traditional high-temperature solid-state reaction method to fabricate the K_(0.495)Na_(0.520)NbO_(3),K_(0.480)Na_(0.535)NbO_(3)and K_(0.475)Na_(0.540)NbO_(3)(abbreviated as KNN-1,KNN-2,and KNN-3,respectively)lead-free ion deficient ceramics for understanding the influence of ionic deficiency on the crystalline structure and dielectric/piezoelectric properties of the samples.X-ray diffraction patterns of these samples exhibited a perovskite tetragonal phase.Dielectric anomalies around 287℃and 471℃were identified as ferroelectric to ferroelectric and ferroelectric to paraelectric-transition temperatures for KNN-2 at 1 kHz.It was found that the composition KNN-2 exhibit relatively high Curie temperature i.e.,471℃.The conductivity plots confirm that the activation energies are frequency-dependent.The impedance behavior in our ceramic samples can be analyzed with the bulk/grain effect.The slope of Z′with temperature shows negative temperature coefficient of resistance(NTCR)type behavior in proposed KNN ceramics material.展开更多
基金Project supported by the European Union’s Horizon 2020Research and Innovation Programme under the Marie Sklodowska-Curie grant agreement(778070)
文摘In this paper,we report on the crystal structure and magnetic properties of the nano structured Baordered phases of rare-earth manganites obtained from the optimally doped solid solutions Ln0.70Ba0.30MnO3(Ln=Pr,Nd).The materials were studied by X-ray diffraction,scanning electron microscopy,energy dispersive spectroscopy and SQUID-magnetometry techniques.It is found that states with different degrees of cation ordering in the A-sublattice of the ABO3 perovskite can be obtained by employing special conditions of chemical treatment.In particular,reduction of the parent compounds results in the formation of a nanocomposite containing ferrimagnetic anion-deficient ordered phase LnBaMn2O5.Oxidation of the composite does not change an average size of the nanocrystallites,but drastically alters their phase composition to stabilize ferromagnetic stoichiometric ordered phase LnBaMn2O6 and ferromagnetic superstoichiometric disordered phase Ln0.90Ba0.10MnO3+δ.It is shown that the magnetic properties of the materials are determined by the joint action of chemical(cation ordering)and external(surface tension)pressures.
基金supported by the Russian Science Foundation(project#15-19-20038)supported by the European Commission under the 7th Framework Programme through the‘Research Infrastructure’action of the‘Capacities’Programme,NMI3-II Grant number 283883’+2 种基金supported by the U.S.Department of Energy,Office of Basic Energy Sciences,Division of Materials Sciences and Engineering under Award FG02-07ER46417(FX and LQC)by the NSF MRSEC under Grant No.DMR-1420620(F.X.and V.G.)the Center for Nanophase Materials Sciences,which is a DOE Office of Science User Facility,CNMS2016-061.
文摘We construct a Landau-Ginzburg thermodynamic potential,and the corresponding phase diagram for pristine and slightly doped bismuth ferrite,a ferroelectric antiferromagnet at room temperature.The potential is developed based on new X-ray and neutron diffraction experiments complementing available data.We demonstrate that a strong biquadratic antiferrodistortive-type coupling is the key to a quantitative description of Bi_(1−x)La_(x)FeO_(3) multiferroic phase diagram including the temperature stability of the antiferromagnetic,ferroelectric,and antiferrodistortive phases,as well as for the prediction of novel intermediate structural phases.Furthermore,we show that“rotomagnetic”antiferrodistortive-antiferromagnetic coupling is very important to describe the ferroelectric polarization and antiferrodistortive tilt behavior in the R3c phase of BiFeO_(3).The Landau-Ginzburg thermodynamic potential is able to describe the sequence of serial and trigger-type phase transitions,the temperature-dependent behavior of the order parameters,and the corresponding susceptibilities to external stimuli.It can also be employed to predict the corresponding ferroelectric and antiferrodistortive properties of Bi_(1−x)La_(x)FeO_(3) thin films and nanoparticles by incorporating the gradient and surface energy terms that are strongly dependent on the shape,size,and preparation method.
基金the DST(INT/RUS/RFBR/P-299)New DelhiRFBR(#17-58-45026 IND_a)Moscow for financial support.
文摘In this research paper,we utilized the traditional high-temperature solid-state reaction method to fabricate the K_(0.495)Na_(0.520)NbO_(3),K_(0.480)Na_(0.535)NbO_(3)and K_(0.475)Na_(0.540)NbO_(3)(abbreviated as KNN-1,KNN-2,and KNN-3,respectively)lead-free ion deficient ceramics for understanding the influence of ionic deficiency on the crystalline structure and dielectric/piezoelectric properties of the samples.X-ray diffraction patterns of these samples exhibited a perovskite tetragonal phase.Dielectric anomalies around 287℃and 471℃were identified as ferroelectric to ferroelectric and ferroelectric to paraelectric-transition temperatures for KNN-2 at 1 kHz.It was found that the composition KNN-2 exhibit relatively high Curie temperature i.e.,471℃.The conductivity plots confirm that the activation energies are frequency-dependent.The impedance behavior in our ceramic samples can be analyzed with the bulk/grain effect.The slope of Z′with temperature shows negative temperature coefficient of resistance(NTCR)type behavior in proposed KNN ceramics material.
基金National Natural Science Foundation of China(52102133)Natural Science Foundation of Jiangsu Province,China(BK20210354)+1 种基金Fundamental Research Funds for the Central Universities(30921011217)Young Elite Scientists Sponsorship Program by CAST(2021-2023QNRC001)。
