Exploration of Possible Novel Phases in Ge-Sn System Using LHDAC Y. A. Sorb # , N. R. Sanjay Kumar # , N. V. Chandra Shekar # , M. Sekar # , T. R. Ravindran # , N. Subramanian #@ and P. Ch. Sahu # # High Pressure Physics Section, CMPD, Materials Science Group Indira Gandhi Centre for Atomic Research, Kalpakkam - 603 102, Tamil Nadu Germanium (Ge) is a semiconductor with a band gap of 0.72 eV and diamond cubic structure, whereas Tin (Sn) is a semimetal with tetragonal β-Sn structure at ambient pressure and temperature. The thermodynamic solubility of Sn in Ge is less than 0.5 at %, while that of Ge in Sn is zero [1]. This is probably due to the large mismatch between the Ge and Sn atomic radii. Ge 1-x Sn x alloys are thus unstable and their synthesis requires non-equilibrium conditions. Ge 1-x Sn x alloys with diamond cubic structure have attracted many due to the prediction of their direct band gap tunability and potential application as infrared detectors. Electronic structure calculations predict the appearance of a α-phase solid solution for Ge-Sn under pressure [2]. Synthesis of microcrystalline Ge 0.78 Sn 0.22 thin films by pulsed UV laser annealing of sputter deposited amorphous Ge 0.70 Sn 0.30 has also been reported [3]. Here we report the results of our attempts to synthesize Ge-Sn alloys using different experimental techniques at different pressures and temperatures. Ge:Sn in 1:1 at ratio was first heated inside the tri-arc furnace and annealed at 700 0 C for 72 hours. A significant weight loss of ~ 40 % was observed. X-ray diffraction done on this sample showed only Germanium peaks, indicating the absence of Sn within the limits of the technique. Next a pelletized sample of Ge:Sn in 1:1 atomic ratio was heated with a CO 2 laser (T ~2000 K) at ambient pressure. The sample showed signs of excellent heating due to good absorption of the CO 2 laser. The X-ray diffraction pattern showed no observable change after heating indicating no reaction or alloying between Ge and Sn. Hence, the high pressure-high temperature route using laser heated diamond anvil cell (LHDAC) technique [4] was attempted to see if application of high pressure can induce favourable enthalpy changes for formation of new phases. Ge:Sn in 1:1 atomic ratio in the form of pellet of size 100µm×100µm was loaded in a diamond anvil cell in Ar pressure medium and was pressurized up to 6 GPa . The pressurized sample was heated by focusing the CO 2 laser for about 20 minutes at a temperature of 2000 K. Micro-Raman studies on the retrieved sample showed that the Ge peak at the wave number 300 cm -1 was missing and a new peak at 201.47 cm -1 was observed. Also, a redshift of the characteristic Sn peak was observed that can be probably due to incorporation of Ge atoms in the Sn lattice under high pressure and high temperature. The appearance of a new band and the disappearance of Ge band may be due to: (i). the formation of a solid solution or a compound or (ii). phase transformation in Ge itself. Further experiments are in progress to resolve this. References: 1. R.W. Olesinski and G.J. Abbaschian, J. Phase Equilibria 5 (1984) 265. 2. Toshinobu et al., Solid State Communications 67 (1988)155. 3. S.Oguz et al., Appl. Phy. Lett. 43 (1983) 848. 4. N.Subramanian et al., Current Science 91 (2006) 175. Acknowledgement: The authors thank Shri L. M. Sundaram for his help in performing experiments, Shri V. Kathirvel and Miss. Dayana Lonappan for their in data analysis. They thank Shri P. Chandra Mohan for his help in micro-Raman studies. They also thank Dr. A.K.Arora, Dr. C.S. Sundar and Dr. Baldev Raj for their encouragement and support. @ Presently at Geophysical Laboratory, Carnegie Institution of Washington, Washington DC, USA