J. Kumar

Vibrational spectra of Y3Al5O12 crystals grown from Ba- and Pb-based flux systems

Abstract The IR and Raman vibrational spectra of yttrium aluminum garnet (YAG) single crystals grown from Ba- and Pb-based flux systems have been recorded. The existence of AlO 4 and AlO 6 characteristic vibrational bands confirms the garnet structure. The spectra of the two samples are compared with the spectra recorded for YAG crystals grown from pure melt and the results are discussed.

Growth and spectroscopic characterization of NdAl3(BO3)4 crystals grown using BaO-B2O3 flux

Caracterisation de NdAl 3 (BO 3 ) 4 par microanalyse par sonde electronique, spectrometrie IR et Raman

Thermodynamics and nucleation behaviour in the system Y2O3-Al2O3-Y3Al5O12

Thermodynamic and nucleation behaviour of the Y2O3-Al2O3-Y3Al5O12 system has been studied. The change in free energy on the formation of a single YAG molecule from a stoichiometric melt of the Y2O3-Al2O3 system at equilibrium is evaluated numerically as a function of temperature. The chemical potentials of the species in the system are evaluated using the regular solution model. The interfacial tension between YAG(S) and Y2O3-Al2O3(L) is determined by calculating the excess energy associated with the interface. The thermodynamic data investigated are used to determine the nucleation parameters such as size, the free energy of formation of a critical nucleus for various possible shapes of clusters as a function of supercooling for different values of interfacial tension, and the shape factors which lead to the understanding of the nucleation phenomena of YAG.

Infrared and raman studies on neodymium pentaphosphate and metaphosphates

The infrared and Raman spectra of crystalline samples of NdP5O14, NaNdP4O12 and KNdP4O12 are recorded. The spectra are analysed on the basis of vibrations of P=O, P-O, PO2 and P-O-P groups. The P4O124− ion has cyclic structures both in NaNdP4O12 and KNdP4O12 crystals. It has been inferred that the P-O-P bridges are stronger in metaphosphates.

Thermal and electrical studies of pure and doped sodium fluoroborate single crystals

Les courbes de conductivite electrique en fonction de T (300 K≤T≤538 K) de NaBF 4 purs et dopes au nickel et au calcium presentent une discontinuite prononcee autour de T=501 K qui doit etre attribuee a une transition de phase. Pour preciser ce point, des etudes par calorimetrie differentielle a balayage ont ete faites