The defect density waves in Zr _0.98 Sn _0.02 TiO ₄ single crystal with incommensurately modulated structures: Neutron diffraction study

Abstract

We demonstrate the formation of defect-density waves in incommensurately modulated phases of Zr0.98Sn0.02TiO4 single crystal using neutron diffraction. A new state of the modulated structure can be explained in terms of a superposition of several modulation waves along a single crystallographic direction.

Comment on “The defect density waves in Zn 0.98 Sn 0.02 TiO 4 single crystal with incommensurately modulated structures: Neutron diffraction study” by Y. Park

“…In ref. [1], Park claims to present for the first time direct structural evidence of defect density waves (DDW) by using Zn 0.98 Sn 0.02 TiO 4 and gives an interpretation of memory effects in incommensurate systems. In a publication [2] that predates [1] we have presented diffraction evidence for the formation of DDW and of a memory effect in incommensurately modulated structures for the first time using single-crystal thiourea (SC(NH 2 ) 2 ).…”

“…[1], Park claims to present for the first time direct structural evidence of defect density waves (DDW) by using Zn 0.98 Sn 0.02 TiO 4 and gives an interpretation of memory effects in incommensurate systems. In a publication [2] that predates [1] we have presented diffraction evidence for the formation of DDW and of a memory effect in incommensurately modulated structures for the first time using single-crystal thiourea (SC(NH 2 ) 2 ). It was shown that additional satellites in the diffraction pattern form due to the superposition of coexisting waves and that the memory effect reflects an equality of the periods of the coexisting structural modulations near the temperature of thermal stabilization.…”

“…In the case of Zn 0.98 Sn 0.02 TiO 4 presented by Park with the incommensurate phase at high temperatures (1093-1423 K) the figures contain mistakes. Figure 1b in [1] shows two peaks (2q th , q th + q st ) in the positions corresponding to the second-order satellites and just one peak in place of the third-order satellite (3q th ). However, for a superposition of waves there ought to be three peaks (2q th , q th +q st , 2q st ) in the positions of the second harmonics (see fig.…”

“…2. Unfortunately, Park provides no explanation for the absence of the additional high-harmonic satellites and this arises some doubt concerning the validity of the experiment in [1].…”