3. HCP O Example: Be, Mg, Zn, Cd, Zr, Hf Ti( low temperature) 2n=×12+×2+3=6 2 CN=12 a5=0.74 32 =1.633 CN=12=0.743. HCP CN 12 0.74 1.633 3 8 2 3 3 2 ) 2 ( 2 2 2 = =  = =       = +   a c a c a • • • • • • • • • • • • • • • • •  Example: Be, Mg, Zn, Cd, Zr, Hf Ti( low temperature)  n＝  CN＝12  ξ＝0.74 2 3 6 2 1 12 6 1  +  + =