Beta‐gadolinium molybdate, β‐Gd₂(MoO₄)₃, is ferroelectric and ferroelastic with a Curie temperature of about 160°C and is paramagnetic with a moment of

{7.98 μ}_{B}

. β‐Gd₂(MoO₄)₃ crystallizes in the orthorhombic system with space group

Pba2

and four formulas in the unit cell. The lattice constants at 298°K are

a = 10.38582 ± 0.00014, b = 10.41861 ± 0.00010

, and

c = 10.70039 ± 0.00004 Å

. The integrated intensities of 14 490 reflections were measured with PEXRAD, within a hemisphere of reciprocal space of radius

(\sin {θ) / λ = 1.02 Å}^{−1}

. The crystal structure was solved by interpretation of Patterson and Fourier series and refined by the method of least squares, using a total of 2545 symmetry independent Fmeas. The final agreement factor

R

is 0.089, based on isotropic thermal vibrations for all atoms. X‐radiation exposure introduces appreciable nonrandom error in the Fmeas. The structure consists of three crystallographically independent discrete sets of (MoO₄)²⁻ tetrahedra; one set is oriented with apex oxygen atoms pointing along

+ c

, a second has apex oxygens pointing along

− c

, and a third has a pseudo‐4̄ axis parallel to

c

. The Gd ions occupy GdO₇ polyhedra. The average Mo–O distance is 1.753 Å, the average Gd–O distance is 2.332 Å. The spontaneous polarization P_s is antiparallel to the sense of the polar crystallographic

c

axis: The calculated value, assuming point charges of Gd³⁺ and (MoO₄)²⁻, is − 0.26 × 10⁻² Cm⁻². The experimental value is about 0.2 × 10⁻² cm⁻². The interchange of axes in ferroelastic switching and the polarity reversal is due to a single process involving small displacements of all atoms. The crystal belongs to the three‐dimensional class of ferroelectrics. The phase transition is represented by:

Π PP (4̄2m) F_{c} F_{c} P (mm2)

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