Growth And Physical Properties Of Eu₂InTe₅ Single Crystal

The search for new functional materials with excellent performance,especially single-crystal materials,is of a great significance and fundamental for the development of condensed matter physics,material science and optoelectronic engineering.In this paper,we successfully grew Eu₂In Te₅ single crystals by the Flux method,analyzed their crystal structures and elemental occupancies by single-crystal X-ray diffraction and X-ray energy spectrum analysis,and investigated their electrical,magnetic and thermoelectric properties by physical properties measurement system（PPMS-Dyna Cool）,Magnetic Property Measurement System（SQUAD MPMS-3）,and low-temperature optical thermostat,respectively,and proved that this new Eu₂In Te₅ single crystal might be a good thermoelectric material.On this basis,we investigated the optical properties of Eu₂In Te₅ single crystal such as reflectance spectra and photo conductivity spectra using Fourier infrared spectroscopy,fiber optic spectroscopy and in situ gold plating techniques.On the other hand,we successfully prepared Eu_1.6Nd_0.4In Te₅ single crystals by the substitution of Nd for Eu,indicating that the physical properties of Eu₂In Te₅ can be further tuned by doping in different elemental positions.These findings provide a promising system for future applications in thermoelectric and optoelectronic technology.The main results and achievements are as follows:（1）Structural analysis:The successfully synthesized Eu₂In Te₅ new compound has a crystallographic structure in tetragonal space group I4/mmm（No.139）with cell parameters a=b=4.5911（5）?and c=24.390（4）?.A occupancy disorder has also been observed in Indium atomic sites.（2）Electromagnetic properties:The resistivity and hall effect measurement show that Eu₂In Te₅ is a metal with low carrier concentration,with a resistivity of about 1.12×10^-2Ω?cm at room temperature,which is higher than that of ordinary metals.At 350 K,the Hall coefficient of the sample is about-1.13×10^-7 m³/C,the carrier mobility is about 11.8 cm^-2/V?s,and the carrier concentration is about 5.53×10¹⁹ cm^-3,respectively.The carrier concentration is about 3～4 orders of magnitude lower than that of common metals.The resistivity data for Eu_1.6Nd_0.4In Te₅ shows an insulator state with 0.74Ω?cm at room temperature.Such high resistivity is not suitable for thermoelectric material.Both Eu₂In Te₅ and Eu_1.6Nd_0.4In Te₅ single crystals have antiferromagnetic phase transitions,and the transition temperature T_Nof Eu₂In Te₅ and Eu_1.6Nd_0.4In Te₅ is about 7.3 K and 5.3 K,respectively.（3）Thermoelectric properties:We got a negative Seebeck coefficient（S）with a value as high as-270μV/K at 300 K,which further indicates that Eu₂In Te₅ is an electron-dominated carrier.Compared with other good thermoelectric materials,the S value of Eu₂In Te₅ is much high.Thermal conductivity（к）rises from 0.25 W m^-1K^-1 at 2 K to 1.67 W m^-1 K^-1 at 300 K,which is comparable to that of thermoelectric materials in practical applications.The electronic thermal conductivityк_e is calculated according to the Wiedemann-Franz law,and its value was found to be almost zero,indicating that the thermal conduction is mainly caused by lattice vibrations,i.e.,phonon scattering,which is most probably related to the disorder of In atoms.（4）Optical properties:The room-temperature-reflectance-spectrum of Eu₂In Te₅has a small spike near 200 cm^-1 as an infrared activated phonon response,and the reflectance rises rapidly near 0.9 as the frequency approaches 0,indicating that the sample has resistance close to the metallic behavior;the photo conductance spectrum has low values at low frequencies,and its DC conductivity is about 0.013Ω?cm when extrapolated to 0 frequency,and the peak at 5500 cm^-1 shows a typical energy jump.The reflectance and photo conductivity spectra are consistent with the above-mentioned resistivity measurements,proving that it is a metal with low carrier concentrations.（5）Nd Doping:The synthesized Eu_1.6Nd_0.4In Te₅ single crystals by Nd element doping of Eu₂In Te₅ is an insulator,indicating that the new single-crystal Eu₂In Te₅ we discovered has a large range of modulation,which lays a good foundation for further research on functional materials.