X-ray powder diffraction and electron diffraction studies of the thortveitite-related L phase, (Zn,Mn)2V2O7

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• The phase gamma-Zn3(VO4)2 is a minor component in zinc oxide-based varistor materials.
• This phase is found in the pseudo-binary Mn2V2O7-Zn2V2O7 system.
• Previous crystallographic data for this phase were limited and potentially inaccurate.

Purpose of the Study:

• To accurately characterize the crystal structure of the L phase, (Zn(1-x)Mn(x))2V2O7.
• To correct erroneous crystallographic parameters previously reported for this phase.
• To investigate the relationship between the L phase and related thortveitite-type structures.

Main Methods:

• X-ray powder diffraction (XRD) pattern analysis.
• Electron diffraction pattern analysis.
• Rietveld refinement of XRD data.
• Convergent-beam electron diffraction (CBED).

Main Results:

• The L phase is identified as (Zn(1-x)Mn(x))2V2O7, with x ranging from 0.188 to 0.538.
• Previously reported lattice parameters (a, c, beta) for this thortveitite-related phase were found to be incorrect.
• Rietveld refinement determined a monoclinic C lattice with Z=6 and precise parameters: a=10.3791(1), b=8.5557(1), c=9.3539(1) Å, beta=98.467(1)°.
• Space group determination indicated Cm, differing from the previously suggested C2/m, possibly due to subtle oxygen displacements.

Conclusions:

• The crystallographic data for the L phase, (Zn(1-x)Mn(x))2V2O7, have been corrected.
• The space group is determined to be Cm, refining previous assignments.
• Further investigation is needed to fully understand the structural relationship with beta'-Zn2V2O7.