The vibrational spectroscopy investigation of phase transitions in NdF3 crystal is reported. Spectra were obtained in temperature range from 300 to 10 K. It has been shown that, down to 10K, the orthorhombic tysonite structure of NdF3 trifluoride remains stable

Ershov, A. A.

Krylov, A. S.

Oreshonkov, A. S.

Shestakov, N. P.

Strikina, E. A.

Voronov, V. N.

Vtyurin, A. N.

Siberian Federal University Digital Repository

Vibrational spectra of NdF3 crystal A.S. Oreshonkov1,2, A.S. Krylov1,2, N.P. Shestakov1,2, V. N. Voronov1,A.A. Ershov1,*, E.A. Strikina1, A.N. Vtyurin1,2 1Kirensky Institute of Physics, SB RAS, 660036, Krasnoyarsk, Russia 2Siberian Federal University, 660079, Krasnoyarsk, Russia Keywords: trifluorides, tysonite structre, Raman spectroscopy, Infrared spectroscopy Running head: Vibrational spectra of NdF3 crystal * Corresponding author: E-mail: ershov@iph.krasn.ru, Phone: +7 391 249 4510, Fax: +7 391 243 8923 Vibrational spectra of NdF3 crystal The vibrational spectroscopy investigation of phase transitions in NdF3 crystal is reported. Spectra were obtained in temperature range from 300 to 10 K. It has been shown that, down to 10K, the orthorhombic tysonite structure of NdF3 trifluoride remains stable. Introduction The NdF3 crystal belong to the rare-earth trifluoride crystals with the tysonite structure ReF3 (Re = La, Ce, Pr, Nd, space group P–3c1, Z = 6), which are extensively studied due to their wide applications in fiberoptics, as an active medium of solid-state lasers, sensors and scintillators [1-5]. Unit cell structure of NdF3 crystal [6] is shown in Fig. 1. According to [7, 8] ReF3 crystals with tysonite structure undergoes a structural phase transition to high-pressure phase Cmma around 20 GPa. On the other hand, the quantum mechanical simulations [9] and in situ X-ray diffraction [10] shows less-distorted I4/mmm structure for high-pressure phase of LaF3 crystal. The crystal structure of La, Ce, Pr and Nd triflourides is stable until melting [10]. The melting point of NdF3 crystal is 1410 K. The aim of this work was to perform the investigation of vibrational spectra of NdF3 crystal in a wide temperature and pressure range looking for some features of structural phase transitions. Experimental Single crystals of NdF3 were grown by Bridgeman– Stockbarger method at the hot zone temperature 1400 C. The starting material was NdF3 of spectral purity grade. The growth was performed in evacuated and sealed platinum ampoule. Temperature gradient inside the heater was 30 K/cm, and the pulling rate was 0.8 mm/hour. As-grown single crystal samples were of several millimeter size and had several growth facets of rather high optical quality, the latter being varying for different facets. No strange reflections were observed with X-ray. Before measurement, as-grown crystals were polished to produce surfaces with perfect optical quality. Raman spectra were collected using the polarized radiation of a 488 nm Ar+ laser (Spectra-Physics Stabilite 2017) in the wavenumber region between 10 and 800 cm–1. The spectra were recorded on a Horiba Jobin Yvon T64000 spectrometer. The temperature studies were performed using an ARS CS204–X1.SS closed cycle helium cryostat in the temperature range of 13 – 300K. The accuracy of temperature stabilization during spectra measurement was <0.2 K. The samples for the far IR range was prepared by mixing of melted NdF3 powder and polyethylene, pellet was made using pellet press. The spectra in the mid-IR range were collected from potassium bromide (KBr) pellet samples, KBr was used instead of polyethylene. The spectra were obtained with Vertex 80V IR spectrometer (Bruker). The temperature studies were performed using an OptistatTM AC-V cryostat in the temperature range of 10 – 286. Results and discussion Mechanical representation of the P–3c1 trigonal phase at Brillouin zone centre of NdF3 crystal is: ГMech = 5A1g+5A1u+7A2g+7A2u+12Eu+12Eg, acoustic and optic modes: Γacoustic = A2u +Eu, Γoptic = 5A1g+5A1u+7A2g +6A2u+11Eu+12Eg, Infrared and Raman active modes ΓRaman = 5A1g+12Eg, ΓInfrared = 6A2u+11Eu. The Raman spectra and mid-infrared spectra of the NdF3 crystal recorded at ambient condition are shown in Fig. 2 and the frequencies observed are listed in Table 1. To calculate the NdF3 vibrational spectrum we used simulation package LADY [11]. Complete spectra of the NdF3 crystal obtained within the framework of simplified version of the Born-Karman model [12]. Within this model, only the pair-wise interactions and bond-stretching force constants 22REA∂∂=  (E – energy, R – bond length) are considered. Simplified version of the Born-Karman model implies that A depends on R and the A(R) dependencies are the same for all atom pairs: A= λexp(–rij/ρ), where rij is the interatomic distance, and λ and ρ are the parameters characterizing selected pair interaction. To find the parameters of the model the special optimization program was written and tested for several compounds [13-15]. The crystal lattice stability conditions were taken into account. The parameters obtained for NdF3 crystal are shown in Table 2. Temperature transformation of Raman spectra is shown in Fig. 3. Crystal cooling leads to reduction of line widths, and to the appearance of the line about 45 cm–1. According to the NdF3 lattice dynamics calculations three Eg mode should appear in the region below 100 cm–1. Two of them are can be clearly seen in Fig. 3 at 36 and 75 cm–1 at room temperature. Third line should exits near 50 cm–1. Thus, it can be assumed that the appearing of the line near 50 cm–1 can be connected with it intensity increasing. No any significant changes in Raman spectra devoted to the structural phase transitions are observed. The IR spectra of the NdF3 compound at different temperatures are shown in Fig. 4. It can be seen that, down to 10K, the infrared spectra do not exhibit noticeable changes that could be attributed to structural phase transitions too. Thus, it can be argued that the crystal structure is stable from 300 to 10K.    Conclusion As a result of these investigations, we can conclude that NdF3 crystal do not undergo the structural phase transitions in the temperature range 300–10K. No any significant changes in vibrational spectra devoted to the structural phase transitions are observed. The number of active spectral lines is an agreement with the selection rules and the lattice dynamics calculation. Acknowledgements This study was partially supported by the Ministry of Education and Science of the Russian Federation and the “Krasnoyarsky regional fund of scientific support and scientific-technical activity”.  References [1] A. Kaminskii, Laser Crystals, Berlin: Springer (1990) [2] S. Krause, W. Moritz and I. Grohmann, Sens. Actuators, B, 1994, 18, 148–154. [3] S. Ye, B. Zhu, J. Luo, J. X. Chen, G. Lakshminarayana and J. R. Qui, Opt. Express, 16, 8989 (2008) [4] A.A. Kalinkin, A.A. Kalachev, V.V. Samartsev, Laser Physics, 13, 1313 (2003). [5] F. Wang and X. G. Liu, Chem. Soc. Rev., 2009, 38, 976–989 [6] E.M. Diniz, C.W.A. Paschoal, Solid State Communications, 136, 538 (2005) [7] T.I. Dyuzheva, L.M. Lityagina, G.B. Demishev, N.A. Dendeliani, Journal of Alloys and Compounds, 335, (2002), 59–61. [8] T.I. Dyuzheva, L.M. Lityagina, G.B. Demishev, N.A. Dendeliani, Inorganic Materials 39 (2003) 1198–1202. [9] B. Winkler, K. Knorr and V. Milman, J. Alloys Compd., 2003, 349, 111–113. [10] Wilson A. Crichton, P. Bouvier, B. Winkler and A. Grzechnik, Dalton Trans. 39, 4302 (2010) [11] Smirnov, M. B.; Kazimirov, V. Yu. JINR communications E 2001,14-2001-159. [12] M. Smirnov, R. Baddour-Hadjean, Li intercalation in TiO2 anatase: Raman spectroscopy and lattice dynamic studies, J. Chem. Phys. 121 (2004) 2348-2355. [13] A.S. Krylov, A.N. Vtyurin, A.S. Oreshonkov, V.N. Voronov, S.N. Krylova, Structural transformations in single crystal Rb2NaYF6: Raman scattering study, J. Raman Spectr. 44 (5) (2013) 763-769. [14] Y.V. Gerasimova, A.S. Oreshonkov, A.N. Vtyurin, A.A. Ivanenko, L.I. Isaenko, A.A. Ershov, E.I. Pogoreltsev, Imfrared absorption investigation of the role of octahedral groups upon the phase transition in the Rb2KMoO3F3 crystal, Phys. Solid State 55 (11) (2013) 2331-2334.  [15] Zhiguo Xia, M.S. Molokeev, A.S. Oreshonkov, V.V. Atuchin, Ru-Shi Liu, Cheng Dong, Crystal and local structure refinement in Ca2Al3O6F explored by X-ray diffraction and Raman spectroscopy, Phys. Chem. Chem. Phys. 16 (2014) 5952-5957.    Fig. 1: Structure of NdF3 crystal: a) projection on the ab plane, b) perspective view Fig. 2: The Raman spectra and mid-infrared spectra of the NdF3 crystal Fig. 3: Temperature transformation of Raman spectra of the NdF3 crystal Fig. 4. IR spectra of the NdF3 crystal at different temperatures  Fig.1.   Fig.2.   Fig. 3.   Fig. 4.  Table 1: Experimental and calculated Raman and Infrared frequencies, and band assignments for NdF3 crystal. Table 2. Parameters of the interatomic interaction potential.  Symm. Type Raman exp 13K (cm–1) Raman exp 300K (cm–1) Raman calc. 300K (cm–1) Symm. type IR exp 300K (cm–1) IR Calc 300K (cm–1) Eg 37 36 36 A2u  38 Eg 45  53 Eu 105 41 Eg 78 75 81 Eu 132 58 A1g 123 120 84 A2u  75 A1g 140 138 129 A2u 163 116 Eg 146  141 Eu 176 121 Eg 151  164 A2u 212 137 A1g 169 165 176 Eu  140 Eg 209 207 181 Eu 253 165 Eg 219  199 Eu  181 Eg 245 240 248 Eu 294 217 A1g 308 306 295 A2u  238 Eg 316  296 Eu 345 252 Eg 327 319 322 Eu 367 295 Eg 382  372 Eu 397 311 Eg 388 384 398 A2u 432 336 A1g 412 407 401 Eu  381 Table 1.  Interactions λ, aJ/Å2 ρ, Å Nd – F1 544.6 0.340 Nd – F2 321.6 0.286 Nd – F3 400.6 0.363 F1 – F1 345.3 0.379 F1 – F2 242.8 0.330 F1 – F3 196.8 0.323  Table 2.  

Vibrational spectra of NdF3 crystal

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Vibrational spectra of NdF3 crystal

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