Localized modes due to H- in Cesium Bromide

Localized modes due to H- in Cesium Bromide

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

ETRASCT' 14 Conference Proceedings

Chetna Chowdhary, Nidhi Varshney, Rakesh kothari

Dept. of Physics

Jodhpur Institute of Engineering & Technology,

Jodhpur, India

chetna.chowdhary@jietjodhpur.com, nidhi.varshney@jietjodhpur.com, rakesh.kothari@jietjodhpur.com

Abstract Localized modes due to U-center in Cesium Bromide have been studied by Green function technique. Defect space consisting of impurity atom alone was considered. Using group theory, symmetry coordinates were constructed and analytical expressions were derived for various modes of vibrations in terms of Greens function of the perfect lattice and the perturbation matrix as a result of defect. Mass change at the defect side as well as the change in short range interaction due to the presence of the defect is taken into account. The change in short range force interaction parameter has been compared with changes in this parameter in other Alkali Halides.

Keywords Localized modes, Green functions, Site symmetry.

1. INTRODUCTION

   Vibrational properties of substitutional and

   impurities have been well discussed in Alkali Halide. Comparatively less studies have been done on the Caesium Halides and this is the motivation for this subject.

2. METHOD OF CALCULATIONS AND RESULTS:

   Impurity atom (single atom) defect space was considered. Considering the symmetry involved, the expression for triply degenerate F1U mode is-

   A= [1-g0M2]3/8g0—————-(1)

   Here g0= Gxx(000,-; 000, -; 2)——————-(2)

   M= Mhost- Mdefect ————————(3)

   A= (Parameter A for the defect-host bond) (Parameter A for perfect lattice)–(4)

   Gxx(000,-; 000, -; 2) refers to Green function of the perfect crystal

   The results are displayed in table 1 along with the experimental values.

   	A	A
   363 (Ref. 2)	8.39 (Ref. 4)	-5.27

   Table 1 Local-mode frequencies of H- ion in CsBr

   represents experimental value of local mode frequency in cm-1 .

   A is the short-range interaction parameter.

   A is the change in A, which gives fit to observed

   frequency.

   A and A are in units of e2/2 V of the given crystal (RbBr); e is electronic charge and V is the volume of the unit cell.

3. DISCUSSION

It is seen from the above table that softening in short- range parameter is of the order of 63%. It may be noted that it varies from 8% in KBr : Cl to 64% in KI:Na.

In the present investigation we have just considered impurity atom (1 atom) defect space.

For more realistic computation, one must consider defect space consisting of defect atom and eight nearest neighbours. This work is in progress. It is hoped, our results will find the application in the study of single ion frequency impurities in these crystals.

Acknowledgment

Our special thanks to Prof. (Dr.) R.K. Gupta for encouragement and continuous guidance for the research as without his motivation this could not be possible.

We are also thankful to Er. Navneet Agarwal & Prof (Dr.)

G.S. Raghuvanshi for providing such facilities.

We are grateful to members of organizing committee for giving an opportunity to present this paper. Our departmental colleagues deserve rightful thanks.

References

1. M.V. Klevin, Physics of color centres, edited by W.

   Beall Fowler: Academic, New York, 1968

2. H. Dotsch and S.S. Mitra, Physics rev, 178, 1492 (1969).

3. R. K. Gupta and A. K. Singh, Physics status solid (b) (Germany), 91,697 (1979)

4. S.Rolandson and G. Raunio, Physics revision, B4, 4617 (1971)

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