Pressure-dependent X-ray diffraction of the multiferroics RMn₂O₅

The room-temperature structural properties of the RMn₂O₅ multiferroics have been investigated under pressure, using powder X-ray scattering and density functional theory (DFT) calculations. It was possible to determine the lattice parameters and the main atomic positions as a function of pressure. Good agreement was observed between the X-ray and DFT results for most of the determined crystallographic data. From the DFT calculations, it was possible to infer the pressure evolution of the exchange interactions, and this analysis led to the conclusion that the onset of the q = (½, 0, ½) magnetic structure under pressure is related to the increase in the J₁ super-exchange terms (due to the reduction in the Mn—O distances) compared with the Mn—R exchange interactions. In addition, the 1D antiferromagnetic character of the compounds should be reinforced under pressure.

Computing details

Program(s) used to refine structure: FULLPROF.

(I)

Crystal data

Mn2O5Pr	c = 5.7154 (5) Å
Mr = 330.78	V = 374.28 (5) Å^3
Orthorhombic, Pbam	Z = 4
Hall symbol: -P 2 2ab	Mo Kα radiation, λ = 0.710000 Å
a = 7.5666 (6) Å	T = 300 K
b = 8.6545 (6) Å

Data collection

Homemade diffractometer	Scan method: step
Radiation source: rotating-anode X-ray tube	2θmin = 6.287°, 2θmax = 42.360°, 2θstep = 0.009°

Refinement

Rp = 1.280	3858 data points
Rwp = 1.729	10 parameters
Rexp = 6.495	0 restraints
RBragg = 2.757	(Δ/σ)max = 0.002

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Pr	0.1457 (3)	0.1735 (3)	0.00000	0.00000*
Mn1	0.00000	0.50000	0.2544 (11)	0.00000*
Mn2	0.4114 (6)	0.3531 (7)	0.50000	0.00000*
O1	0.00000	0.00000	0.26905	0.00000*
O2	0.16565	0.44544	0.00000	0.00000*
O3	0.13373	0.43770	0.50000	0.00000*
O4	0.40463	0.20287	0.25507	0.00000*

Geometric parameters (Å, º)

Pr—O1	2.4115 (19)	Mn1—O4	1.8983 (1)
Pr—O2	2.436 (3)	Mn2—O1	1.9514 (2)
Pr—O4	2.4553 (18)	Mn2—O3	2.225 (5)
Mn1—O2	1.977 (5)	Mn2—O4	1.911 (4)
Mn1—O3	1.813 (5)
O2—Mn1—O2	81.1 (3)	O1—Mn2—O3	95.7 (2)
O2—Mn1—O3	96.9 (2)	O1—Mn2—O4	87.4 (2)
O2—Mn1—O3	175.7 (2)	O1—Mn2—O4	160.5 (2)
O2—Mn1—O4	87.8 (2)	O3—Mn2—O4	101.8 (2)
O2—Mn1—O4	90.3 (2)	O4—Mn2—O4	97.5 (2)
O3—Mn1—O3	85.3 (3)	Mn2—O1—Mn2	98.0 (2)
O3—Mn1—O4	88.4 (2)	Mn1—O2—Mn1	98.98 (2)
O3—Mn1—O4	93.5 (2)	Mn1—O3—Mn1	94.7 (2)
O4—Mn1—O4	177.5 (2)	Mn1—O3—Mn2	132.4 (2)
O1—Mn2—O1	82.5 (2)	Mn1—O4—Mn2	125.6 (2)