What is provided is a layered double hydroxide crystal for achieving higher ion-exchange capacity than that of the related art. The layered double hydroxide crystal 1 according to the present embodiment is represented by Formula (1) and composed of a plurality of crystal grains 10 each of which has a lamination structure in which a plurality of plate-shaped crystals (11), (11), . . . are laminated, in which particle sizes of the plurality of crystal grains (10), (10), . . . are uniform on a microscale.
[Ni.sup.2+.sub.1xFe.sup.3+.sub.x(OH).sub.2].Math.[(Cl.sup.).sub.X/2](1) (Where, 0.25

Various single crystals are disclosed including sapphire as well as methods of forming the same. A method of forming a crystalline structure is disclosed as well. The method can include providing a melt in a crucible having a die. The die can include a ventilation opening. The method can further include growing the crystalline structure from the die using an enclosed seed. The single crystals can have desirable geometric properties, including a length greater than a diameter greater than a thickness.

Various single crystals are disclosed including sapphire as well as methods of forming the same. A method of forming a crystalline structure is disclosed as well. The method can include providing a melt in a crucible having a die. The die can include a ventilation opening. The method can further include growing the crystalline structure from the die using an enclosed seed. The single crystals can have desirable geometric properties, including a length greater than a diameter greater than a thickness.