| In the 21 st century,functional material is one of the most important guiding and basic materials with the development of high and new technology.In the world,functional material has always been very active in the development and research and its progress promotes the rapid development of high-tech industries,such as information,electronics,machinery,chemical industry,aerospace,communication and so on.As a kind of new electronic materials,Rare-earth orthoferrite material has been widely applied in the field of information industry and electronic sensors.It has great research value and application prospect,and is always one of the hot spots in condensed matter physics and materials science field.The mechanical spectrum(MS)is a well-known technologyfor the study of phase transitions and dynamics of many kinds of microscopic process,such as point defects,dislocations,grain boundaries and domain walls,etc.,in the solid materials.In this paper,we present the mechanical,dielectric and magnetic properties of YFe1-xMnxO3,Pr1-xSrxFeO3 and SmFe1-xCrxO3 ceramics.With the audio internal friction spectrum measurement and combining with the dielectric and magnetic properties,we investigate some physical problems in RFeO3 ceramics such as the valence state change of transition metal ions,polaron hopping,oxygen vacancy freezing,magnetic spin reorientation,spin glass,charge order,multiferroic(magnetodielectric or magnetoelectric),element doping or substitution effect and to explore the origin of the corresponding mechanical spectrum.Specific content can be divided into the following sections:1.Study in YFeO3 and YFe1-xMnxO3:YFe03 has a distorted perovskite structure with space group Pnma and antiferromagnetic transition temperature TN?640 K;YMn03 is multiferroic material,with high ferroelectric transition temperature Tc-900K,antiferromagnetic transition temperature is low TAr-70 K.P.Mandal et al,found that the solid solution of them shows magnetoelectric effect and magneticdielectric effect.To study the effect of Mn-substituted,the mechanical spectra of Mn-substituted yttrium orthoferrite YFe1_xMnxO3(x=0,0.2,0.3,0.4)ceramics were performed at kilohertz from 100 to 360 K.Two internal friction(IF)peaks are observed around 150 K and 230 K,respectively and both the IF peaks exhibit frequency dispersion behaviors.The IF peak around 150 K is associated with a step increase of the modulus and its mechanical relaxation rate follows the Vogel-Fulcher relation with ?0=4.45×10-11 s,E?=0.03 eV and TVF=155 K.After Hydrogen peroxide treatment,the intensity of the internal friction peak is restrained,and this IF peak can be explained in terms of a freezing of oxygen vacancies after excluding the possible magnetic spin glass transition.Another IF peak around 230 K presents a relaxation behavior and it follows Arrhenius law.Furthermore,the relaxation behavior was verified by the dielectric spectrum and it can be ascribed to the charge carrier hopping between Fe2+ and Fe3+,and the existence of the Fe2+ ions was confirmed in the samples by the XPS results.The intensity of P2 peak is strengthened and the activated energy decreases with increasing Mn content.More two-site electron hopping processes appear with the increase in Fe2+ content rate as increasing of Mn doping.The decrease in activation energy for electron hopping between Fe2+ and Fe3+ may indicate that the hopping is a collective behavior instead of an individual one.The correlation for the hopping electrons increases with an increase of the Fe2+ ions concentration and the activation energy thus decreases.2.Study of the Pr1-xSrxFeO3 ceramics:The charge order(CO)was observed in R1-xSrxFeO3 with x=2/3,Zhu et al,found that the presence of CO was characterized by a substantial modulus softening above the CO transition temperature TCO and dramatic stiffening below TcO.It is of considerable interest to investigate whether the CO state also exists in the components besides x=2/3.The mechanical spectra of Pr1-xSrxFeO3(x=0.5,0.55,0.6)ceramics were performed at kHz frequencies from 100 to 350 K.An internal friction(IF)peak around 130 K associated with a modulus defect was observed and a reduced Young's modulus kink around 200 K appeared also.This IF peak exhibits frequency dispersion behavior.The dielectric relaxation behavior was also observed in the temperature range of 50-150 K.The activation energy of 0.14 eV,0.13 eV and 0.11 eV is derived from the Arrhenius law for Pr0.5Sr0.5FeO3,Pr0.45Sr0.55FeO3 and Pr0.4Sr0.6FeO3 samples,respectively.Both the dielectric peak and internal friction peak can be ascribed to the charge carrier hopping between Fe3+and Fe4+ The Fe4+ ions were also confirmed in the samples by the XPS measurement.The kink in the reduced Young's modulus around 200 K shows no obvious frequency dispersion behavior and the magnetization measurement confirms that it associates with a spin-glass transition.In addition,another dielectric anomaly at 200 K may be ascribed to the magnetodielectric(MD)effect.However,no CO was observed in our samples and it needs further study.3.Study of SmFe1-xCrxO3:SmFeO3 belongs to the orthogonal structure with space group Pnma and antiferromagnetic Neel temperature TN?670 K,spin orientation temperature TSR-480 K.Lee et al,found that ferroelectric polarization of SmFeO3 single crystal appears near the room temperature and the ferroelectric polarization will keep until the antiferromagnetic Neel temperature.SmCrO3 has the same crystal structure and magnetic characteristics as SmFeO3 with antiferromagnetic ordered temperature TN?197 K,spin orientation temperature near 40 K.Rajeswaran et al,found that SmCrO3 exhibited dielectric anomaly near the spin orientation temperature and antiferromagnetic Neel temperature.Literature also reported that the solid solution SmCr1-xFexO3(0?x?0.5)exhibited the rich magnetic characteristics with antiferromagnetic Neel temperature(x=0.5)around 310 K.It appears especially important that to investigate the mechanical spectrum,dielectric properties and magnetic dielectric effect around room temperature of the solid solution.Polycrystalline samples SmFe1-xCrxO3(x=0.0,0.1,0.3,0.5)were prepared via traditional solid state sintering method.The mechanical spectra(IF)were measured at kHz.There are three internal friction peaks(labeled as P1,P2 and P3,respectively)in the temperature of 150 K,250 K and 300 K for all the samples and the intensity of these peaks increases with the increasing of the Cr content.For the dielectric properties,there are two sets of dielectric relaxation behavior in the temperature range of 150-250 K and 270-400 K.The activation energy of them are 0.26 eV,0.25 eV,0.24 eV and 0.22 eV and 0.63 eV,0.36 eV,035 eV and 0.33 eV from the Arrhenius law for x=0.0,x=0.1,x=0.3,and x=0.5 samples,respectively.According to the results in literatures,we suggest that the P1 peak should be corresponding to the freezing of oxygen vacancies,the P2 peak around 250 K and the dielectric relaxor behavior around 150-250 K may originate from charge carrier hopping between Fe2+ and Fe3+,the P3 peak and the relaxor behavior around 270-400 K are ascribed to the second-ionization of oxygen vacancies according to the activation energy values.The intensity of IF peak is strengthened with increasing Cr content and it is ascribed to the increase of oxygen content.Thermal analysis shows that the introduction of Cr can make the antiferromagnetic Neel point shifts to the low temperature.The difference between magnetic phase transition temperature and the IF temperature rules out the possibility of the internal friction peak related to the magnetic transition.In addition,in our experiment,there is no magnetic dielectric effect in the sample with x=0.5. |
PDF Full Text Request