Crystal structural, electric and magnetic studies on the misfit layer compounds “LnMS 3” (Ln=rare-earth metal; M=Ti,V,Cr)

Abstract

A series of misfit layer “LnMS 3” were prepared where Ln=La,Ce,Pr,Nd,Sm,Gd and M=Ti,V,Cr. There was an upper limit of the ionic radius ratio R(M)/ R(Ln)=0.61 for the formation of the misfit layer structure. Powder X-ray diffraction data of “LaCrS 3” was indexed with the monoclinic LaS sublattice (a=5.942 A ̊ , b=5.776 A ̊ , c=11.078 A ̊ , β=95.38∘) , the pseudo-monoclinic CrS 2 sublattice (a=5.936 A ̊ , b=3.449 A ̊ , c=11.063 A ̊ , β=94.78∘) and their supercell. The temperature dependence of the dimension of each subcell indicates that the interaction between LaS and CrS 2 layers becomes stronger at lower temperature. The ( hk0) precession photograph of the “LaVS 3” single crystal was also interpreted in terms of two component meshes, tetragonal and orthohexagonal subcells. “LnVS 3” with Ln=La,Ce,Pr,Nd were isostructural with “LaCrS 3”. Their transport properties were semiconductive and the activation energy around room temperature decreased with a decrease of ionic radius of Ln. The semiconductive property changed to metallic at low temperature in a range from 150 to 200 K. In the case of Ln=Sm and Gd, the semiconductor-metal transition was not observed down to 17 K.