Electron microscopy
 
c/a Ratios in hcp Structures
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For an ideal HCP (hexagonal close-packed) structure, the c/a ratio is 1.63299. However, this ratio, in practice, varies depending on the specific composition in the HCP structures. Table 1906 lists some examples of c/a ratios in some HCP crystals.

Table 1906. Examples of c/a ratios and slip systems in some HCP crystals.

Crystal c (Å) a (Å) c/a ratio

Primary slip system

Preferred slip planes in order of ease of slip Melting temperature
(Tm, K)
Am (Americium)     3.229      
Be 3.5833 2.2866 1.568

Basal

(0001), (10-10), (10-11) 1,560
Ca 6.52 3.98 1.64     1,116
Cd 5.61 2.97 1.886 Basal (0001), (10-10), (10-11) 594
Ce     3.24      
Co     1.628 Basal (0001)  
Dy 5.67 3.58 1.58      
Er 5.59 3.55 1.57      
Gd 5.79 3.63 1.59      
Hf 5.05 3.19 1.58 Prismatic    
Ho 5.61 3.58 1.57      
La     3.218      
Li     1.637      
Lu 5.55 3.50 1.58      
Mg 5.21 3.21 1.623 Basal (0001), (10-11), (10-10) 922
Na     1.634      
Nd (Neodymium)     3.226      
Os (Osmium)     1.579      
Pr (Praseodymium)     3.223      
Re     1.615 Prismatic/Basal (10-10), (0001)  
Ru 4.28 2.70 1.58 Prismatic    
Sb 11.2 4.3 2.605      
Sc 5.27 3.31 1.59      
Sr     1.635      
Tb (Terbium) 5.69 3.60 1.58      
Tc (Technetium)     1.604      
Ti (α) 4.68 2.95 1.587 Prismatic (10-10), (0001), (10-10)  
Tl (Thallium)     1.598      
Tm 5.55 3.53 1.57      
Y 5.73 3.61 1.571 Prismatic (10-10), (0001)  
Zn 4.95 2.66 1.856 Basal (0001), (10-10), (11-22) 693
Zr 5.15 3.23 1.593 Prismatic    
Cu1-xZnx alloy
(0.78 < x < 0.86)
    1.56      
GeTe 10.71 4.17 2.568      
GeSb2Te4 41.0 4.25 9.647      
Ge2Sb2Te5 17.2 ~ 18.27 4.25 4.047 ~ 4.299      
Ge3Sb2Te6 62.6 4.25 14.73      
Sb2Te (δ) 17.633 4.272 4.128      
Sb2Te2 23.9 4.26 5.610      
Sb4Te3 (γ) 41.55 4.26 9.754      

 

 

 

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