%0 Journal Article
%A Pina Martínez, Carlos Manuel
%A Woensdregt, Cornelis F.
%T Hartman–Perdok analysis of crystal morphology and interfacetopology of β-LiNaSO4
%D 2001
%@ 0022-0248
%U https://hdl.handle.net/20.500.14352/57121
%X The trigonal b-LiNaSO4 low temperature polymorph belongs to the family of double sulphates with general formulaLiMSO4 (M ¼ Na; NH4, Rb,y), which have very specific electrical properties. In this paper we present the b-LiNaSO4theoretical growth morphology based on the Hartman–Perdok theory. Therefore, Periodic Bond Chains (PBCs) havebeen identified in order to determine the influence of the crystal structure on the crystal morphology. The shortest PBCis parallel to /1 00S and consists of a one-step proto-PBC with sulphate(I)–cation–sulphate(I, 1 0 0) strong bonds. Allthe other PBCs are built up from strong bonds in two or more consecutive steps, e.g., sulphate (I)–cation–sulphate(II)–cation–sulphate (I, u vw). The corresponding F forms are in order of decreasing dhkl : f1 0 %11 0g; f1 0 %11 1g; {0 0 0 2},f1 0 %11 2g; f1 1 %22 0g ¼ f2 %11 %11 0g; f1 1 %22 2g ¼ f2 %11 %11 2g; y For many F forms several different slice configurations can bedefined. Attachment energies have been calculated in electrostatic point charge models with formal charges. In addition,the effect of covalent S–O bonds on the growth forms has been taken into account by decreasing the effective charge onoxygen, qO: The theoretical growth form of b-LiNaSO4 based on attachment energies calculated in the LiNaS6+O42point charge model shows the hexagonal prism f1 0 %11 0g; the hexagonal pyramid f1 0 %11 1g and the pedion (0 0 0 1). Whenthe influence of the S–O bond decreases (LiNaS4+O41.5 model), the habit is slightly less elongated parallel to the c-axisdue to the increased relative morphological importance of the pyramid form with respect to the prism. When we assumethat the hexagonal prism face grows with halved slices d20%220 and thus using the attachment energies of E20%220a instead ofthose of E10%110a ; the growth forms changes drastically by the absence of the hexagonal prism form in both models. Inaddition, the trigonal prism f1 1 %22 0g is present as a minor form on this LiNaS4+O41.5 model with halved d20%220 slices.Experimentally grown LiNaSO4 crystals show habits that deviate from the theoretical growth forms. This must be dueto external factors such as supersaturation and interaction of the crystal surface with the aqueous solutions during thegrowth. Growth experiments confirm that the growth morphology is strongly influenced by the degree ofsupersaturation.
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