Light Scattering Studies Section

Hydrogels & Thermo-responsive Nanogels

Significant Results

Phase Behavior of Poly(N-isopropylacrylamide) Nanogel Dispersions JNN2009

Nanostructured materials

Nanostructured materials have given a completely new dimension to materials research, in view of the ability to tailor their properties by changing the grain size. Optical and vibrational properties of nanoparticles of semiconductors and insulators are investigated. These include self standing powders, composites and thin film. Studies are aimed at synthesizing nanocrystalline system with high efficiency for radiative recombination for potential application as luminescent devices and radiation detectors. For reviews on phonon confinement see: JRS2007B & ENN2004  

 Significant results

  · Substitutional disorder in mixed-crystal nanoparticles JRS2009

· Phonon confinement in stressed silicon nanoclusters JNN2009

· Surface optical phonons in InN nano-wires and belts APL2008

· Electron-phonon interaction in ZnO nanocrystals SSC2008

· Optical phonon confinement in nano-materials (Review) JRS2007b

· Annealing of CdS nanocrystals PHYE2006

· Phonon confinement in nanostructured materials (Review) ENN2004

Negative Thermal Expansion Materials

Negative thermal expansion (NTE) materials are technologically important from the point of view of developing low and zero thermal expansion materials. Large NTE of cubic zirconium tungstate has motivated studies on the mechanism in this compound and on related network structures. The phonons responsible for the NTE in zirconium tungstate were identified PRL2000 PRL2001 and their anharmonicities were quantified PRB2003. Several new tungstates and molybdates with similar network structure have been synthesized and studies on their structural stability as a function of pressure and temperature have been undertaken. Single-phase Al2-xScx(WO4)3 solid-solution has been synthesized and characterized for possible zero thermal expansion.

Significant results

· Soft modes responsible for NTE identified in Zn(CN)2 PRB2007c

· Controversy on structure of Zn(CN)2 resolved JRS2007a

· Evidence of disorder in cubic zirconium tungstate JPCM2007

· Zero expansion in aluminum-scandium tungstate solid solution JEC2006

· Anharmonic phonons in zirconium tungstate identified PRB2003

Pressure induced amorphization & decomposition (including phase transitions)

Although the phenomenon of pressure-induced amorphization has been the subject of intense research for almost 20 years, a complete understanding of its causes and mechanisms has not emerged. Orientational disorder (OD) of polyatomic ions has been found to be the cause of PIA in several double sulphates. A recent model SSC2000 suggested that in many systems this could arise if a pressure-induced decomposition (PID) is kinetically hindered. This model could explain amorphization in many systems JPCM2001 and could also predict amorphization in several others JPCM2002. The predicted amorphization at ambient-temperature and decomposition at high-temperature has been confirmed in bismuth orthogermanate JPCM2004b and scandium molybdate JAP2005. On the other hand, zirconium vanadate undergoes pressure-induced solid-state decomposition even at ambient temperature PRB2007. For a review see: EnricoFermi2002.

Significant results

· First evidence of solid-state decomposition at ambient temperature in ZrV2O7 PRB2007a

· Pressure-amorphized zirconium tungstate: A precursor to decomposition JPCM2004a

· First report of two-stage amorphization in Sc2(MoO4)3 SSC2004

· High-pressure high-temperature stability of scandium molybdate JAP2005

· Predicted amorphization/decomposition confirmed in bismuth germanate JPCM2004b

· Hysteresis in Orthorhombic-Monoclinic phase transition in Sc2(MoO4)3 JPCM2005

· High-temperature phase transition in indium tungstate JAP2004

Pressure-induced amorphization and decomposition in ZrV2O7: A Raman spectroscopic study

T. Sakuntala, A.K. Arora, V. Sivasubramanian, R. Rao, S. Kalavathy, and S.K. Deb

Phys. Rev. B 75, 174119:1-6 (2007).



Pressure-amorphized state in zirconium tungstate: A precursor to decomposition

A.K. Arora, V.S. Sastry, P.C. Sahu and T.A. Mary

J. Phys.: Condens. Matter 16, 1025-1031 (2004).



Two-stage amorphization of scandium molybdate at high-pressure

A.K. Arora, R. Nithya, T. yagi, N. Miyajima and T.A. Mary

Solid State Commun. 129, 9-13 (2004).



Amorphization and decomposition of scandium molybdate at high pressure

A.K. Arora, T. Yagi, N. Miyajima, and T.A. Mary

J. Appl. Phys. 97, 013508:1-8 (2005)



Stability of bismuth orthogermanate at high pressure and high temperature

A.K. Arora, T. Yagi, N. Miyajima, and R. Gopalakrishnan

J. Phys. Condens. Matter 16, 8117-8130 (2004)



Low temperature Raman spectroscopic study of scandium molybdate

T.R. Ravindran, V. Sivasubramanian, and A.K. Arora

J. Phys. Condens. Matter 17, 277-286 (2005)



Structural phase transition in indium tungstate

V. Sivasubramnian, T.R. Ravindran, R. Nithya, and A.K. Arora

J. Appl. Phys. 96, 387-392 (2004).