Z. Phys. B 94, 261-264 (1994) ZEITSCHRIFT FORPHYSIK B 9 Springer-Verlag 1994 Superconductivity induced phonon anomalies in the Raman spectra of Zn and Ni doped YBazCu307 R. Gaji~, S.D. Devil, M.J. Konstantinovi~, Z.V. Popovi~ Institute of Physics, Maksima Gorkog 118, P.O. Box, YU-11001 Belgrade,Yugoslavia Received: 7 June 1993 Abstract. Here we present Raman spectra of YBa2(Cul_xZnx)30 7 and YBa2(Cul_~Nix)307 as a func- tion of temperature and Zn or Ni content. The tempera- ture dependence of two modes at 340 and 440 cm-1 is analyzed. Similarly to the infrared measurements it is found that Zn substantially suppresses the superconduc- tivity induced phonon softening whereas, Ni does not affect much that effect. Moreover, the superconductivity induced phonon stiffening of the 440 cm 1 mode com- pletely disappeared with the Zn doping. We find this be- haviour might support the model where Zn acts effective- ly as a magnetic pair breaker. PACS: 74.25.Gz; 74.25.Ke; 78.30.Er 1. Introduction Among all 3 d substitutions of copper in YBazCU3OT, Zn and Ni are specially interesting. As adjacent elements to copper in the periodic table, Zn and Ni have similar chem- ical characteristics and, despite the lack of a full concen- sus, it seems that they occupy preferentialy Cu(2) atoms in the CuO 2 layers. The main difference between Zn and Ni, is the filled 3 d shell of Zn 2+ in contrast to unfilled one of Ni 2+ and Cu 2+. Therefore, the Zn doping enables one to investigate the role of the 3 d holes in the two- dimensional CuO 2 layers. It is well known that the Zn doping suppresses su- perconductivity in YBa2Cu307 much stronger than Ni does [1-4]. The same is valid for the phonon softening of the infrared active modes in these materials [5-7]. While the phonon softening of the 310cm -1 infrared mode in YBa2(CUl_xZnx)307 disappeares already for x = 0.03, this effect is almost independent of the Ni con- tent in YBa2(CUl_xNix)307 . The correlation between these two effects points to the same source and raise again questions about the significance of the electron-optical phonon coupling in the high-temperature supercon- ductors. In order to complete the picture of the superconduc- tivity-induced optical phonon anomalies in the Zn and Ni doped YBa2Cu307, we investigated the temperature dependence of two Raman modes, associated with the c-axis vibrations of oxygens in CuO2 planes, at 340 and 440 cm 1 as a function of Zn and Ni content. 2. Experimental The ceramic samples of YBa2(CUl_xMx)307, M =Zn, Ni with x= 0.01, 0.03 and 0.05 were prepared by usual solid state reaction technique, already described in [5, 6]. Their structure caracterization was performed with X-ray Siemens diffractometer D-500 using Cu-K~ radia- tion. Diffraction patterns confirm that all samples are monophase and orthorhombic with small amount of im- purities (less than 1% due BaCuO 2 and Y2BaCuOs). Electrical resistivity measurements (the four-probe method) revealed that the superconducting transitions are sharp within 3 K for all samples. The values of T~ (zero resistance) for Zn and Ni are 75, 50, 35 K, and 86, 81, 75 K respectively, for x=0.01, 0.03 and 0.05. The Raman spectra were excited by the 514.5 nm line of an Argon ion laser with the average power of 25 mW. The laser beam was focused on the sample using a cylin- drical lens. All spectra were obtained in a backscattering geometry with the aperture of the collecting objectiv of f= 1 : 1.4. The monochromator used was U1000 (Jobin- Yvon) with the 1800 grooves/ram holographic gratings. As a detector we used the Pelltier effect cooled RCA 31034 A photomultiplier with convential photon count- ing system. The samples were held in a closed-cycle cryostat (Leybold) equipped with the low-temperature controler (Leybold LTC 60) and evacuated by a turbo- pump. Temperature range was 10 to 300 K with the spec- tral resolution of 1 cm- 1. 3. Results and discussion The Raman spectra were measured in the spectral range from 290 to 510 cm -1. Some characteristic patterns are presented in Figs. 1 and 2. These spectra resemble to un- doped ones showing that Zn and Ni do not affect much