A survey of the phenomenon of polytypism in crystals

Trigunayat, G. C.

doi:10.1016/0167-2738(91)90200-u

Cited by 105 publications

(79 citation statements)

References 129 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Sharma, Malhotra & Agrawal (1979) have investigated the polytypism of vapourgrown mixed crystals of Cdlz_xBr x and CdI 2_xClx. Recently, a detailed study of the effect of several different dopants, viz Pb, Ga, In, Sn, Br2 and C12, on melt-grown CdI2 crystals has been carried out (Tyagi & Trigunayat, 1988Trigunayat, 1991), yielding concrete information on the effect of impurities on polytype formation and related phenomena.…”

Section: Introductionmentioning

confidence: 99%

“…Later, studies were extended to other polytypic materials such as ZnS, CdI2, micas etc. Several different theories of polytypism have been proposed from time to time (Trigunayat, 1991). Frank's screw dislocation theory (Frank, 1951), coupled with the faulted matrix model (Pandey & Krishna, 1975), has been especially successful in explaining the formation of polytypes of mica (Baronnet & Kang, 1989).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of variation in PbI₂doping on the polytypism of dendritic CdI₂single crystals

Kumar¹,

Trigunayat²

1993

J Appl Cryst

View full text Add to dashboard Cite

Highly pure dendritic single crystals of cadmium iodide, variously (2 to 8%) doped with lead iodide, have been grown from the vapour phase in a vacuum. The study of polytypism and related phenomena in the crystals has been carried out by X-ray diffraction. An uneven high rate of increase in the occurrence of the 12-layered rhombohedral polytype 12R has been found to exist when the amount of PbI2 in the crystals rises from 2 to 8%. Simultaneously, the relative intensity of the 12R reflections has been found to rise rapidly. Another curious feature has been an unusually high frequency of occurrence of a particular high polytype 48H in the heavily (8%) doped crystals. The percentage occurrences of streaking and arcing have been found to be low and to vary slowly with the PbI2 content of the crystals. The observed polytypism has been explained in terms of the nucleation of two different thermodynamically stable end-member polytypes, 4H and 12R, of CdI2 and PbI2, respectively.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of variation in PbI₂doping on the polytypism of dendritic CdI₂single crystals

Kumar¹,

Trigunayat²

1993

J Appl Cryst

View full text Add to dashboard Cite

show abstract

“…The phenomena of streaking and arcing arise from (i) the presence of random stacking faults in the crystal and (ii) arrangement of edge dislocations into small-angle tilt boundaries in the crystal, respectively (Trigunayat, 1966). If a large number of faults is created in the Brdoped crystals, a large fraction of them is also expected to remain randomly distributed in the structure, after their possible rearrangement into a polytype structure, which agrees with the observation, viz the ®gures for the occurence of streaking are 47, 11 and 0% (nil), for the Br-doped, the Pb-doped and the undoped crystals, respectively (Kumar & Trigunayat, 1993a,b, 1991b.…”

Section: Resultsmentioning

confidence: 99%

“…), only needle-shaped crystals of AgI show polytypism (Prager, 1983;Cochrane, 1967). During the last four decades, a great deal of work has been done on the polytypism of the MX 2 -type compounds CdI 2 , PbI 2 and CdBr 2 , almost all of which have been carried out on platy crystals (Trigunayat, 1991). For the ®rst time, dendritic crystals of the richly polytypic materials CdI 2 and PbI 2 were grown from the vapour phase by Kumar & Trigunayat (1991a,b) and the effect of growth conditions on their polytypism was reported.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Polytypism and Related Phenomena in CdBr₂-Doped Dendritic Single Crystals of Cadmium Iodide

Kumar¹,

Trigunayat²

1998

Acta Cryst Sect A

View full text Add to dashboard Cite

Dendritic single crystals of CdI 2 , doped with 3% CdBr 2 , were grown from vapour phase in vacuum. The crystals exhibited well developed dendritic morphology. They were characterized by X-ray diffraction for their polytypism and related phenomena of streaking and arcing. The CdI 2 common polytype 4H was found to occur exclusively in 28% of cases and in combination with the poylytype 12R in the rest of the cases. The frequency of occurrence of streaking and arcing were found to be rather high, viz 47 and 25%, respectively. The results point to a large-scale formation of dislocations and the consequent stacking faults inside the crystals, presumably created due to stresses produced in the host structure by the introduction of doped ions. Optical and scanning electron-microscopic study of the surface features shows a well developed dendritic morphology conforming with the hexagonal symmetry of the crystals.

show abstract

Curious Variations in Energy Gap of Polytypic CdI2 and PbI2 Crystals on Laser Irradiation

Nayak

Bhalla

Kumar

et al. 1999

phys. stat. sol. (b)

View full text Add to dashboard Cite

Crystals of CdI2 and PbI2 were grown by zone melting. They were subjected to argon ion laser irradiation. Both time and intensity of radiation were systematically varied. The crystals of CdI2 were of type 4H while those of PbI2 were of type 2H. Their energy gaps were determined by UV spectrophotometry. The CdI2 crystals showed a linear variation of energy gap with intensity of radiation (0 to 125 mW), with the energy gap value decreasing from 3.28 to 3.11 eV, when the exposure time was kept fixed (7 min). When the time of exposure was varied, with the intensity of radiation fixed at 50 mW, the energy gap initially decreased from 3.28 to 3.07 eV and then gradually rose to be restored to the original value, thus showing a nonlinear variation. For the PbI2 crystals, the energy gap steadily decreased from 2.53 to 2.02 eV, when the intensity of exposure was varied. However, the value drastically decreased from 2.53 to 1.04 eV for the case of variation of exposure time. The results have been explained in terms of changes in phonon frequency, amount of absorption and anisotropy of thermal conductivity of the material.

show abstract

A survey of the phenomenon of polytypism in crystals

Cited by 105 publications

References 129 publications

Effect of variation in PbI₂doping on the polytypism of dendritic CdI₂single crystals

Effect of variation in PbI₂doping on the polytypism of dendritic CdI₂single crystals

Polytypism and Related Phenomena in CdBr₂-Doped Dendritic Single Crystals of Cadmium Iodide

Curious Variations in Energy Gap of Polytypic CdI2 and PbI2 Crystals on Laser Irradiation

Contact Info

Product

Resources

About

A survey of the phenomenon of polytypism in crystals

Cited by 105 publications

References 129 publications

Effect of variation in PbI2doping on the polytypism of dendritic CdI2single crystals

Effect of variation in PbI2doping on the polytypism of dendritic CdI2single crystals

Polytypism and Related Phenomena in CdBr2-Doped Dendritic Single Crystals of Cadmium Iodide

Curious Variations in Energy Gap of Polytypic CdI2 and PbI2 Crystals on Laser Irradiation

Contact Info

Product

Resources

About

Effect of variation in PbI₂doping on the polytypism of dendritic CdI₂single crystals

Effect of variation in PbI₂doping on the polytypism of dendritic CdI₂single crystals

Polytypism and Related Phenomena in CdBr₂-Doped Dendritic Single Crystals of Cadmium Iodide