Growth and characterization of undoped, Sr2+-, and Mn2+-doped ammonium tetrachlorozincate

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The effect of chemical non-stoichiometry and γ-irradiation on the unit cell parameters of ammonium tetrachlorozincate (NH 4 ) 2 ZnCl 4 (A 2 ZC 4 ) has been studied. The unit cell parameters of crystal grown from solution with NH 4 Cl/ZnCl 2 molar ratio 1:1, apparently non-stoichiometrric, are nearly the same as those given for ammonium tetrachlorozincate in the literature. The 2:1 ratio is actually 'pseudo-stoichiometric' due to the hygroscopic nature of ZnCl 2 . The unit cell parameters of crystal grown from solution with molar ratio 2:1 match those of the structure (NH 4 ) 3 ZnCl 5 (A 3 ZC 5 ). The habit of the crystal grown in the former case, from solution with excess ZnCl 2 , was different from that of the crystal grown in the later case, from solution with excess (NH 4 )Cl. Between these two limits, a set of four samples were prepared from solutions with an excess of ZnCl 2 of 20, 30, 60 and 80 wt % in order to detect exact stoichiometric composition to grow A 2 ZC 4 . Analysis by X-ray diffraction shows that the first two crystals out of this set are mixed from A 2 ZC 4 and A 3 ZC 5 The third and fourth crystals still contain traces of A 3 ZC 5 . Analysis of the X-ray diffraction was then confirmed by DTA study. Irradiating A 2 ZC 4 with γ-dose of 250 kGy slightly increased the unit cell volume due to imperfections created by irradiation. Two computer programs were used to calculate the lattice constants and the results were compared.

Section: Effect Of γ-Irradiationcontrasting

confidence: 51%

Effects induced by chemical non-stoichiometry and γ-irradiation on the habit and unit cell parameters of ammonium tetrachlorozincate

Gaffar¹,

El‐Fadl²,

Anooz³

2006

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“…The accelerator dose rate is 2 Gy/min and the maximum irradiation dose reached in the present study was 1.26 kGy by systematic accumulation of e-doses using the same sample. This maximum dose is far behind that used by the authors to study the effect of γ-irradiation on transmittance of AZC [18].…”

Section: Methodsmentioning

confidence: 95%

Electron irradiation‐induced effects on optical spectra of (NH₄)₂ZnCl₄: x Sr²⁺ single crystals

Gaffar

El‐Fadl

Anooz

2003

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The effect of electron-beam irradiation with different doses on optical constants of (NH 4 ) 2 ZnCl 4 : x Sr 2+ crystals with x=0.000, 0.020, 0.039, 0.087 or 0.144 wt% has been studied. The optical transmission in the energy range 3.4-6.4 eV was measured hence the absorption coefficient was computed as a frequency function. The absorption coefficient was also calculated as a function of electron-beam dose. Irradiation with e-beam did not affect the allowed indirect type of transition responsible for interband transitions of (NH 4 ) 2 ZnCl 4 : x Sr 2+ crystals. Values of the optical energy gap E g and optical moment E p for electronic interband transition of unexposed and (NH 4 ) 2 ZnCl 4 : x Sr 2+ crystals after e-beam exposure were deduced. The area under the absorption band at 5.30 eV was used to evaluate the effect of e-irradiation on optical parameters of samples with x=0.00, 0.020 or 0.039. A shift in the position and a nonmonotonic change in the intensity of this band with increasing e-beam dose was observed. Changes in the E g value were used to evaluate the effect of e-beam exposure dose on (NH 4 ) 2 ZnCl 4 : x Sr 2+ samples with x=0.087 or 0.144. The obtained results were compared with those obtained for the same crystals after irradiation with different γ-doses.

“…It is worthy to know that exact amount of ZnCl 2 needed for chemical stoichiometry may not be achieved and the growth run may be accomplished in a medium with excess ZnCl 2 . Details about the effect of chemical non-stoichiometry on growth and morphology of AZC may be found elsewhere [14]. The solution was saturated by gradual temperature lowering and by visual observation of the convection close to the test seed suspended in the solution.…”

Section: Methodsmentioning

confidence: 99%

Influence of cationic substitution on lattice constants and optical characterization in solution grown mixed crystals of potassium‐ ammonium zinc chloride

El‐Fadl¹,

Soltan

Shaalan

2006

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Mixed crystals of potassium-ammonium zinc chloride in different concentrations were grown from aqueous solution employing the techniques of slow cooling and controlled evaporation. Powder x-ray diffraction studies were carried out on the grown crystals. The comparison between lattice parameters a, b and c are experimentally determined and calculated by Vegad's law. The concentration of K + ions in the crystals was measured by the atomic absorption technique. The crystal morphology changed considerably by increasing K + concentration. The optical absorption coefficient (α) indicated strong influence changing concentration. The optical energy gap was found to decrease with increasing K + concentration.