Chemical vapor transport method was applied in order to obtain CdCr₂Se₄ and CuCr₂Se₄ single crystals doped with niobium. Binary selenides: Nb₂Se₃ and CdSe or CuSe, respectively, were used as a starting material. Anhydrous chromium chloride was used as a transport agent. Taking into account the site preference energy and cation valency it was assumed that niobium would substitute chromium and proper amounts of substrates were calculated according to the reaction:

4 CdSe + (2-x) CrCl_3(g) +  Nb₂Se₃   → Cd[Cr_2-xNb_x]Se₄  + 3 CdCl_2(g) +  2 NbCl_3(g) + 2 Se_3(g)        for x=0.1; 0.25; 0.5

or

4 CuSe + (2-x) CrCl_3(g) +   Nb₂Se₃   → Cu[Cr_2-xNb_x]Se₄  + 3 CdCl_2(g) +  2 NbCl_3(g) + 2 Se_3(g)       for x=0.1; 0.25; 0.5

The crystallization process was carried out in evacuated quartz ampoules put to the horizontal zone temperature furnace. In case of CdCr_2-xNb_x Se₄ two different temperature gradients were applied: ΔT=10K or  ΔT=100K. In both cases two types of single crystals were obtained: pellets and needles. Single crystals of CuCr_2-xNb_x Se₄ had a shape of regular octahedral. In both cases the crystallization process was successful only for x=0.25.

The chemical composition was verified using scanning electron microscope.   

 Single crystals of different type of shape were chosen for X-ray diffraction measurements on a four – circle diffractometer X-calibur/CCD Oxford Diffraction using graphite monochromated MoKα radiation.  The structure refinement was performed using the SHELXL-97 program package.  

This work is funded from science resources for years 2011-2014 as a research project No N N204 151940.

Chemical vapor transport method was applied in order to obtain CdCr₂Se₄ and CuCr₂Se₄ single crystals doped with niobium. Binary selenides: Nb₂Se₃ and CdSe or CuSe, respectively, were used as a starting material. Anhydrous chromium chloride was used as a transport agent. Taking into account the site preference energy and cation valency it was assumed that niobium would substitute chromium and proper amounts of substrates were calculated according to the reaction:

4CdSe + (2-x)CrCl_3(g) +(2+x)/2 Nb₂Se₃ → Cd[Cr_2-xNb_x]Se₄+ 3CdCl_2(g) + 2 NbCl_3(g) + 2 Se_3(g)        for x=0.1; 0.25; 0.5

or

4 CuSe + (2-x)CrCl_3(g)+ (2+x)/2 Nb₂Se₃  → Cu[Cr_2-xNb_x]Se₄ + 3CdCl_2(g)+2 NbCl_3(g) + 2 Se_3(g)       for x=0.1; 0.25; 0.5

The crystallization process was carried out in evacuated quartz ampoules put to the horizontal zone temperature furnace. In case of CdCr_2-xNb_x Se₄ two different temperature gradients were applied: ΔT=10K or  ΔT=100K. In both cases two types of single crystals were obtained: pellets and needles. Single crystals of CuCr_2-xNb_x Se₄ had a shape of regular octahedral. In both cases the crystallization process was successful only for x=0.25.

The chemical composition was verified using scanning electron microscope.   

 Single crystals of different type of shape were chosen for X-ray diffraction measurements on a four – circle diffractometer X-calibur/CCD Oxford Diffraction using graphite monochromated MoKα radiation.  The structure refinement was performed using the SHELXL-97 program package.  

This work is funded from science resources for years 2011-2014 as a research project No N N204 151940.

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