The Crystal Structure of Metallic Tellurium and Selenium and of Strontium and Barium Selenide

X-ray spectrograms were made using the powder method of Hull, with monochromatic $\mathrm{MoK}\alpha$ rays. Both tellurium and selenium are found to crystallize in simple triangular lattices with axial ratios 1.33 and 1.14, respectively, and with sides of unit basal triangle equal to 4.44 A and 4.34 A, respectively. In each case three atoms are grouped at each corner. The densities computed from these measurements are 6.25 and 4.84, respectively. Strontium selenide and barium selenide both have a simple cubic structure, with cube edges equal to 3.117±.003 A and 3.308±.005 A respectively. In the case of SrSe the ions at the corners are ${\mathrm{Sr}}^{++}$ and ${\mathrm{Se}}^{--}$, and the calculated density is 4.53.