Analysis of infrared reflectivity of Pr2NiO4 single crystal

Analysis of infrared-visible-near-ultraviolet reflectivity of conducting and superconducting oxides

“…4. In this case we do observe a mid-infrared band in the conducting ab-plane but such an absorption is not so evident along the almost insulator c-axis [6). Once again we observe that this extra absorption (near 4000 cm -1 ) in the ab-plane is associated with the presence of free charge carriers introduced by oxygen stoichiometry, This means that possibly this absorption is also polaronic in YBaCuO.…”

High-temperature behavior of infrared conductivity of aPr2NiO4+δsingle crystal

“…In many conducting oxides, the following expression of the dielectric response has been used successfully to reproduce their peculiar optical features over several decades of frequencies: [22][23][24]35,36,38,40,44,45,51 …”

“…It can be clearly seen from this figure that the shape of the reflectivity spectra is not deeply affected by the increase of temperature and looks similar to those previously reported for poorly conducting oxides. 7,22,[30][31][32][33]36,40,43,51 The infrared spectrum of Pr 2 NiO 4.205 at room temperature is well reproduced by the combination of three phonon peaks, an overdamped oscillator in the mid-infrared range ͑ TO Loc = 3800 cm −1 ͒ and an extended Drude's term ͑⍀ p ϳ 900 cm −1 ͒ as shows the comparison between the experimental and fitted spectrum reported in Fig. 3 To reproduce satisfactorily the large spectral weight of this band, LO Loc ϳ 7200 cm −1 is found, such value being of the same order as the one used to fit the reflectivity spectra of a Pr 2 NiO 4.22 single crystal up to 15 000 cm −1 .…”

“…In Pr 2 NiO 4+␦ , the oxygen overstoichiometry ␦ plays a crucial role on its physical and structural properties, [22][23][24][25][26][27][28][29] since insertion of oxygen relaxes the constraints of the undoped distorted compound and creates holes in the NiO 2 planes, [25][26][27] inducing highly anisotropic behavior. 22,24 Pr 2 NiO 4+␦ undergoes a structural phase transition from an orthorhombic symmetry ͑LTO͒ to a tetragonal one ͑HTT͒ at T ϳ 720 K, 26 accompanied by oxygen loss.…”

“…22,24 Pr 2 NiO 4+␦ undergoes a structural phase transition from an orthorhombic symmetry ͑LTO͒ to a tetragonal one ͑HTT͒ at T ϳ 720 K, 26 accompanied by oxygen loss. 25 This structural transition may be also correlated to the electrical behavior change occurring also at T ϳ 720 K, 27 the compound behaving as a semiconductor below this temperature.…”