Exotic Compositional Ordering in Manganese–Nickel–Arsenic (Mn-Ni-As) Intermetallics

Article abstract of DOI:10.1002/anie.202006135

In this work we benefited from recent advances in tools for crystal-structure analysis that enabled us to describe an exotic nanoscale phenomenon in structural chemistry. The Mn_0.60Ni_0.40As sample of the Mn_1?xNi_xAs solid solution, exhibits an incommensurate compositional modulation intimately coupled with positional modulations. The average structure is of the simple NiAs type, but in contrast to a normal solid solution, we observe that manganese and nickel segregate periodically at the nano-level into ordered MnAs and NiAs layers with thickness of 2–4 face-shared octahedra. The detailed description was obtained by combination of 3D electron diffraction, scanning transmission electron microscopy, and neutron diffraction. The distribution of the manganese and nickel layers is perfectly described by a modulation vector q=0.360(3) c*. Displacive modulations are observed for all elements as a consequence of the occupational modulation, and as a means to achieve acceptable Ni–As and Mn–As distances. This modulated evolution of magnetic MnAs and non-magnetic NiAs-layers with periodicity at approximately 10 ? level, may provide an avenue for spintronics.

Full text of DOI:10.1002/anie.202006135

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
International Edition Chemie
www.angewandte.org
Accepted Article
Title: Exotic compositional ordering in Mn-Ni-As intermetallics
Authors: Bruno Gonano, Øystein Slagtern Fjellvåg, Gwaldys Steciuk,
Dipankar Saha, Denis Pelloquin, and Helmer Fjellvåg
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202006135
Link to VoR: https://doi.org/10.1002/anie.202006135

Angewandte Chemie International Edition
10.1002/anie.202006135
COMMUNICATION
Exotic compositional ordering in Mn-Ni-As intermetallics
a
b
c
a
d
Bruno Gonano , Øystein Slagtern Fjellvåg , Gwladys Steciuk , Dipankar Saha , Denis Pelloquin
and Helmer Fjellvåg*a
aCenter for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway
bDepartment for Neutron Materials Characterization, Institute for Energy Technology, PO Box 40, NO-2027, Kjeller, Norway.
cInstitute of Physics, Academy of Sciences of the Czech Republic, v.v.i, Na Slovance 2, Prague 18221, Czech Republic
dLaboratoire CRISMAT, UMR 6508 CNRS ENSICAEN, 6 bd du Maréchal Juin, 14050 Caen Cedex 4, France
Abstract: In this work we benefited from recent advances in tools for
crystal structure analysis that enabled us to describe an exotic
nanoscale phenomenon in structural chemistry. The Mn0.60Ni0.40As
giving rise to face-sharing chains of MnAs
with two octahedra per unit cell. In the ab-plane, the MnAs
octahedra are edge-sharing. Pauli paramagnetic NiAs (space
group P6 /mmc) adopts the same structure type, but with different
6
-octahedra along [001]
6
-
3
x
sample of the Mn1-xNi As solid solution, exhibits an incommensurate
unit cell parameters (due to the different size of Mn and Ni).
compositional modulation intimately coupled with positional
modulations. The average structure is of the simple NiAs type, but in
contrast to a normal solid solution, we observe that manganese and
nickel segregate periodically at the nano-level into ordered MnAs and
NiAs layers with thickness of 2-4 face-shared octahedra. The detailed
description was obtained by combination of 3D electron diffraction,
scanning transmission electron microscopy and neutron diffraction.
The distribution of the manganese and nickel layers is perfectly
described by a modulation vector q = 0.360(3) c*. Displacive
modulations are observed for all elements as a consequence of the
occupational modulation, and as a means to achieve acceptable Ni-
As and Mn-As distances. This extraordinary modulated evolution of
magnetic MnAs and non-magnetic NiAs-layers with periodicity at
The intermediate solid solution between MnAs and NiAs, Mn1-
x
x
Ni As (0 ≤ x ≤ 1), was investigated in the 1980s and revealed an
[
13]
unsolved structural phenomenon for 0.25 ≤ x ≤ 0.75 . A possible
modulation due to Ni ordering was proposed, but no available
technique could confirm or invalidate this speculation. Therefore,
the question of
x
a Mn-Ni-ordering in Mn1-xNi As remained
unanswered. Today, state-of-the-art analytical tools have evolved
to the point that revisiting this system can provide answers. We
here reveal an exotic Mn-Ni-ordering in Mn0.60Ni0.40As, which
appears to represent a phenomenon not earlier observed.
Results and Discussion
Initially, we studied the lattice of Mn0.60Ni0.40As by conventional
electron diffraction (ED), and the data revealed an expected
complex unit cell. Electron diffraction pattern of the [100]-zone
axis shows additional reflections (Fig. 1a) that can be indexed by
an incommensurate modulation vector (q = 0.36 c*), confirming
the presence of additional order in the compound. The
corresponding High-Angle Annular Dark Field (HAADF) image
coupled with local EDX collections yields good elemental
contrasts correlated to Mn and Ni species and reveals two types
of layers perpendicular to the modulation vector [001] (Fig. 1b
and c). We interpret these images as a specific ordering between
Mn and Ni based layers, as supported by energy-dispersive X-ray
spectroscopy mapping (EDX) (Fig. 1b).
~
10 Å level, may provide an avenue for spintronics.
Introduction
Since the discovery of X-rays, scientists have studied atomic
arrangements in solids considering their intrinsic beauty and their
role as the active link between atoms and physical properties of
materials. In a crystal structure, one finds different sites for cations
and anions, reflecting their different chemical properties (i.e. size,
charge, electronegativity, etc.). This gives rise to a huge range of
crystal structure types, from simple to very complex ones among
proteins, organic and inorganic compounds.
The thickness of these layers can be measured in terms of the
number of connected octahedra, being 3-4 for the MnAs and 2-3
for the NiAs slabs of the integrated structure. This creates a
unique nanolayered structure, with the compositional modulation
being a genuine part of the crystal structure of the phase. We note
that the layers appear to be fully occupied by either Mn or Ni,
indicating that the ordering is complete.
Incommensurately modulated crystal structures with their high
complexity, attract a lot of interest in solid-state science. Both
occupancy and position can be modulated. The modulation can
originate from a wide variety of structural perturbations like
[
1]
incommensurate oxygen vacancies ordering , polyhedral
distortions[
2,3]
and compositional ordering . Incommensurate
[4]
modulations are quite well understood in oxides while
[
5–
intermetallics present a challenge in terms of structural analysis
.
Careful analysis of the As-As distances along [001] in the x25M
HAADF image, reveals a distinct difference between the zones
richer in Mn or in Ni (Fig. 1c). Whereas for the brighter layer (Ni-
rich) the As-As distance tends to be shorter, it increases in the
darker Mn-rich regions, according to the longer c-axis of MnAs
7
]
An incommensurate, partial cation occupancy modulation has
[8]
been reported for LaNb0.88
0.12
W O4.06 . This compound has a
modulation linked to a preferential cation nano-segregation of
tungsten atoms. In intermetallics, positional modulation has been
observed in different compounds, e.g. in the Nowotny Chimney-
ladder phases[9–11], that can described as an intertwining between
(
5.8 Å) compared to that of NiAs (5.0 Å). This is supported by the
extracted line profile for the As-As distances in Fig. 1d.
At this point, it is clear that the Mn-Ni ordering is real. We now use
two sublattices. Similar phenomena are present in Cu3+xSi[12]
,
[14]
3
D ED to unveil a structural model. This technique has recently
which displays a very complex incommensurate modulation and
illustrate well the complexity in disclosing structural details for
such systems.
proved his ability to yield valid structural models in complex
[15]
systems
and provide single-crystal diffraction data on small
areas of few hundreds of nanometers, also on powder samples.
It must be mentioned here that 3D ED represents a broad range
of experimental protocols and that this study refers to Precession
Electron Diffraction Tomography (PEDT).
3
Ferromagnetic MnAs (space group P6 /mmc) is an example of a
simple crystal structure derived from ABAB sphere packing of As,
with Mn in octahedral sites formed by closed-packed As-layers,
1
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202006135
COMMUNICATION
Figure 1: a) Electron diffraction of the [100]-zone axis of Mn0.60Ni0.40As
showing satellite reflections, corresponding to an incommensurate
modulation vector along c* (q = 0.36 c*); b) Experimental [100] HAADF
image of Mn0.60Ni0.4As (magnification x8M). Bright dots are related to As
rows while darker and brighter layers represent MnAs and NiAs,
respectively. On the right side, simulated image confirms the goodness of
the structural model. Latter is inserted beside. Top left inset: EDS
spectrum related to recorded zone (Probe) identified by a black box. Top
right inset: EDS mapping evidencing richer zones in Mn (purple) and Ni
First, the average framework of (Mn, Ni)As octahedra is revealed
in agreement with the initially reported structure. The model is
6
[13]
further elaborated by calculating de Wolf sections x3-x4 around
the two atomic sites corresponding to Mn/Ni and As atoms (Fig.
3b). The As site exhibits a displacive modulation along c,
described using a continuous harmonic function. In order to
account for the Mn/Ni ordering along [001], the site shared by Mn
and Ni atoms is split using discontinuous crenel-like functions
associated with one harmonic function.[ Within the resolution of
the 3D ED data, the electron scattering amplitudes for Mn and Ni
are too close to reliably detect a difference in the electrostatic
potential between the domains.
(grey); c) Experimental [100] HAADF image of Mn0.60Ni0.4As (magnification
18]
x25M) showing variations in distances between As atoms from Mn (darker)
and Ni (brighter) layers. A snapshot of the structural model is inserted; d)
Intensity line profile extracted from the HAADF image along [001],
displaying the variations of As-As distances in the MnAs and NiAs layers.
3
D ED shows the expected hexagonal subcell, but also additional
0
For this reason, the centers of the crenels are set to x4 (Mn) = 0.5
reflections at incommensurate positions (Fig. 2a). The reciprocal
space was indexed using the superspace formalism considering
a hexagonal unit cell: a = 3.653(8) Å, c = 5.417(3) Å and with a
modulation vector q = 0.360(3) c* to index satellite reflections up
to first order. As expected from the conventional ED, the
modulation is incommensurate. The volume of the average unit
0
and x4 (Ni) = 0 in order to strain the shortest (longest) distances
for Ni-As (Mn-As). The crenel widths were set according to the
composition: Δ(Mn) = 0.6 and Δ(Ni) = 0.4 (Fig. 3b). For better
visualization of the Mn-Ni stacking sequence, the e-map, as well
as the interpreted model, is represented in an averaged supercell
aꢀ×ꢀbꢀ×ꢀ4c. The main experimental parameters are listed in Table
3
cell (V = 62.67 Å ) is in between the volumes of NiAs (V = 56.7
Å ) and MnAs (V = 68.55 Å ).
1
(SI).
3
3 [16],[17]
. Information on symmetry is
obtained from e.g. the sections 11lm and 0klm of the reciprocal
space for which the extinction conditions l = 2n on 00l and 11lm
are characteristic of a 6 -screw axis along [001] and a c-glide
3
mirror perpendicular to [1-10], respectively (Fig. 2b). These
conditions are compatible with two superspace groups (SSG);
The model exhibits the alternation of two types of blocks with
variable thickness consisting either of layers of MnAs octahedra
or of layers of NiAs octahedra. Dynamical refinements were
carried out against the 3D ED data.
were chosen following the recommendation by Palatinus et al.
RSg(max) = 0.9, S(max)g(matrix) = 0.01ꢀÅ , g(max) = 1.7ꢀÅ .
Because of the rather small unit cell volume and the high
symmetry, the RSg(max) was set to a high value to thereby
include a sufficiently large number of reflections and maintain a
good reflection-to-parameter ratio (Table 1 (SI)). The refinement
gave reliability factors of R/wR(obs/all) = 13.85%/14.65% for N
obs/all = 796/1788 [main: R/wR(obs) = 12.67%/14.28%; 1. order:
R/wR(obs) = 16.24%/15.75%].
6
6
10,11
The included reflections
[20]
−1
P6
solved from the 3D ED data in SSG P6
.360(3) c* and a data coverage of 100% for 0.7ꢀÅ resolution
shell. Our subsequent refinements indicated that the structure is
centrosymmetric P6 /mmc(00γ)0000.
3
/mmc(00γ)0000 and P6
3
mc(00γ)000. The structure was
−1
3
/mmc(00γ)0000 with q =
-1
0
3
The initial solution obtained by charge flipping algorithm is a 3D
map of the electrostatic potential (e-map) represented as
isosurfaces (Fig. 3a).
Figure 2: a) Reciprocal space projected in one-unit cell showing
satellite reflections up to first order (red); b) Sections of reciprocal
space from PEDT data
2
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202006135
COMMUNICATION
This represent a huge improvement compared to what offered in
a kinematical refinement [R/wR(obs/all) = 3.18%/35.39% for N
obs/all = 88/128].
The expected Mn-As and Ni-As bond lengths are reached owing
to the displacive modulations of As and Mn/Ni along the stacking
direction c (Fig. 3d). This information corroborates our initial
observations from HAADF imaging (Fig. 1b and 1c).
The crystal structure of Mn0.60Ni0.40As exhibits an alternation of 3-
4
layers of MnAs and 2-3 layers of NiAs (Fig. 3c), described by a
The collected powder neutron diffraction (PND) pattern shows
-
genuine incommensurate modulation with respect to the chemical
intense reflections at low scattering angle (Fig. 4), e.g. at 0.42 Å
composition. As shown by Fjellvåg et al.[13] the Mn0.60Ni0.40As
1
, which is a first-order satellite reflection from the compositional
sample represents just an arbitrary composition for the Mn1-xNi
x
As
modulation of Mn and Ni. The strong signal of the satellite
reflections is a consequence of the excellent contrast between Mn
and Ni in PND, due to the different signs of their scattering lengths.
Thus, unlike what was feasible with 3D ED data, the sample
composition can be determined with accuracy by Rietveld
refinement of the crenel widths from PND data. The derived
composition of Mn0.598(3)Ni0.402(7)As is in line with the nominal
composition from synthesis.
solid solution where superstructure peaks are observed. The
simulated HAADF image (calculated by JEMS software) based on
the aforementioned incommensurate structure model is included
in Fig. 1b and shows very good compliance with the observed
image. The observed positional modulation of the Mn, Ni and As
atoms along [001] dictates a difference in the cell volume for the
MnAs and NiAs layers, being in agreement with unit cell volumes
of the binary compounds as well as the HAADF images.
The modulation vector obtained from the PND Rietveld
refinements [q = 0.3594(2) c*] is identical to that obtained by 3D
ED [q = 0.360(3) c*]. We note that the results obtained from
refinements of PND and 3D ED data are identical, within statistical
uncertainty. We emphasize that the combination of PND and 3D
ED data was necessary to fully understand the structure as PND
is superior for refining the exact composition, while 3D ED was
needed for structural determination. The final refined structural
model from both data sets is presented in Table 1 and Table 2.
Figure 3: a) [100] projection of the 3D electronic potential map and its
interpretation as a structural model. For better visualization of the layers,
the model is extended along the stacking direction [001]. The Mn and Ni
cations are in octahedral coordination; b) On the De Wolf section x3-x4
calculated around the As site, the cationic site is described with a
continuous harmonic function and split between 2 sites for Mn and Ni
using discontinuous crenel-like functions; c) Extended [110] projection of
the refined structure against PEDT data (dynamical refinement); d)
Variation in Mn – As and Ni - As distances showing the evolution of the
local As environment as function of the modulation.
3
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202006135
COMMUNICATION
Table 1: Unit-cells parameters extracted from refinement of 3D ED data
and neutron diffraction data.
The oxide LaNb0.88W0.12O4.06 has certain similarities to
Mn0.60Ni0.40As by being occupationally modulated. However, there
are significant differences: (i) only occupational modulation is
observed, while Mn0.60Ni0.40As exhibits both occupational and
positional modulation; (ii) the occupational modulation of Mn and
Ni in Mn0.60Ni0.40As leads to a complete segregation into MnAs
0.12
and NiAs regions, whereas LaNb0.88W O4.06 only shows partial
segregation of W; (iii) the architecture of the segregation itself
differs; 2D layers versus 3D network, and (iv) the bonding in the
two cases is very different; metallic versus polar covalent/ionic.
Last, we note that MnAs is ferromagnetic and NiAs is
paramagnetic, which makes the intrinsically nanolayered material
a potential candidate for spintronics.
Table 2. Positional parameters extracted from the dynamical refinement of
3D ED data and neutron diffraction data.
Conclusion
Mn0.60Ni0.40As is, to our knowledge, the first example of a
representative of a solid solution compound where the chemical
composition is directly reflected in an occupational modulation
that is intimately coupled to a positional modulation. It is surprising
that this exotic and unique phenomenon with Mn-Ni occupational
modulation occurs for a phase ideally taking the simple NiAs-type
structure. We stress that this modulation of composition,
materialized by ultrathin layers consisting of edge- and face-
sharing Mn-As octahedra and of Ni-As octahedra, is different from
any other stacking or order/disorder phenomena.
The modulated structure is the genuine crystal structure of
Mn0.60Ni0.40As. The periodic variation in the stacking of 2D layers
of MnAs and NiAs, creates an incommensurate modulation, with
The type of intrinsic “nano-layering” observed for Mn0.60Ni0.40As is
unique. There exist a few examples of related features. It is
reminiscent of the layered ferecrystals that can be described as
an intergrowth between two different types of cation - anion layers,
bonded by weak Van der Walls forces (e.g. m bilayers of SnSe
3-4 thick layers of MnAs and 2-3 layers of NiAs, that in turn
determines the chemical composition of the material. In this work,
we show how the structural model to describe this peculiar
phenomenon can be derived from 3D ED and validated by
refinement of powder neutron diffraction data with excellent Mn/Ni
scattering contrast. The refined composition is in full compliance
with the nominal composition from synthesis. The structure model,
as well as the coupled HAADF-EDS mapping images, shows that
the MnAs layers have a longer c-axis than the NiAs layers, in full
agreement with crystallographic data for the individual binary
compounds.
2 2 1
m
and one trilayer of NbSe , [(SnSe)1+γ] (NbSe ) ). However,
ferecrystals clearly differ from Mn0.60Ni0.40As by being constructed
of weakly bonded building bricks that furthermore can exist as
independent well defined compounds.
The present phenomenon is unlike that of other modulated
compounds. The layers in the Mn0.60Ni0.40As compound are of the
same crystal structure, in contrast to the Nowotny Chimney-
ladder phases. In compounds like Cu3+xSi, the modulation is
positional and is not originating from an ordering between Cu and
Si atoms.
We have demonstrated the existence of
a
fascinating
nanophenomenon in a solid-solution phase, and the ability,
strength and robustness of state-of-the-art tools in crystallography
and methodology to solve and describe complex incommensurate
phenomena, all acting as inspiration for future research. The
modulated feature of strongly magnetic MnAs and non-magnetic
NiAs layers with periodic layer thicknesses at the 1 nm scale, is
likely to attract attention in fields like spintronics.
Figure 4: Experimental (black crosses), calculated (red line) and difference
(blue line) neutron powder diffraction pattern of Mn0.60Ni0.40As according
to Rietveld refinement. Main and satellite Bragg peak positions are
indicated with green and orange sticks, respectively.
4
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202006135
COMMUNICATION
[
26] G. Steciuk, P. Boullay, A. Pautrat, N. Barrier, V.
References
Caignaert, L. Palatinus, Inorg. Chem. 2016, 55, 8881–
[
[
[
1]
2]
3]
J. D. C. McConnell, V. Heine, Phys. Rev. B 1985, 31,
140–6142.
C. J. Howard, M. A. Carpenter, Acta Cryst B 2010, 66,
0–50.
L. J. Gillie, J. Hadermann, O. Pérez, C. Martin, M.
Hervieu, E. Suard, Journal of Solid State Chemistry
8891.
6
Acknowledgments
4
This work is part of the activities of the NAMM project (Novel
Approaches to Magneto-Structural phases transitions in
Metallic systems), supported by the Research Council of
Norway (Grant no. 263241). Authors want to acknowledge
Susmit Kumar, Center for Materials Science and
Nanotechnology, Department of Chemistry, University of Oslo
for fruitful discussions. The authors acknowledge Vivian
Nassif, Inès Puente-Orench and the staff at the D1B beamline,
ILL, France, for beamtime allocation and technical support.
(S)TEM experiments have been performed in the CRISMAT
Lab. (UMR6508, Caen, France) within the frame of the
METSA federation (FR3507). G.S. acknowledges the Czech
Science Foundation through Project No. 19-07931Y.
2
004, 177, 3383–3391.
[
[
[
[
[
[
[
[
4]
5]
6]
7]
8]
9]
L. Norén, R. L. Withers, R. Berger, Journal of Solid
State Chemistry 2000, 151, 260–266.
M. Boström, S. Lidin, Journal of Alloys and
Compounds 2004, 376, 49–57.
H. Lind, M. Boström, V. Petříček, S. Lidin, Acta Cryst
B 2003, 59, 720–729.
S. Y. Piao, L. Palatinus, S. Lidin, Inorg. Chem. 2008,
4
7, 1079–1086.
C. Li, S. S. Pramana, S. J. Skinner, Dalton Trans.
019, 48, 1633–1646.
D. C. Fredrickson, S. Lee, R. Hoffmann, Inorg. Chem.
004, 43, 6159–6167.
2
Conflict of Interest
The authors declare no conflict of interest.
2
10] N. Sato, H. Ouchi, Y. Takagiwa, K. Kimura, Chem.
Mat. 2016, 28, 529–533.
11] F. E. Rohrer, H. Lind, L. Eriksson, A.-K. Larsson, S.
Lidin, Zeitschrift für Kristallographie - Crystalline
Materials 2001, 216, 190–198.
Keywords Solid-State Structures, Intermetallics, Electron
Diffraction, Neutron Diffraction
[
[
[
12] L. Palatinus, M. Klementová, V. Dřínek, M. Jarošová,
V. Petříček, Inorg. Chem. 2011, 50, 3743–3751.
13] H. Fjellvag, A. Kjekshus, A. Andresen, A. Zieba, J.
Magn. Magn. Mater. 1986, 61, 61–80.
14] M. Gemmi, E. Mugnaioli, T. E. Gorelik, U. Kolb, L.
Palatinus, P. Boullay, S. Hovmöller, J. P. Abrahams,
ACS Cent. Sci. 2019, 5, 1315–1329.
[
[
[
[
15] G. Steciuk, L. Palatinus, J. Rohlíček, S. Ouhenia, D.
Chateigner, Sci Rep 2019, 9, 9156.
16] N. Alsén, Geologiska Föreningen i Stockholm
Förhandlingar 1925, 47, 19–72.
17] R. Wilson, J. Kasper, Acta Crystallographica 1964, 17,
9
5-.
18] V. Petříček, V. Eigner, M. Dušek, A. Čejchan,
Zeitschrift für Kristallographie - Crystalline Materials
2
016, 231, 301–312.
[
[
[
19] L. Palatinus, V. Petříček, C. A. Corrêa, Acta Cryst A,
Acta Cryst Sect A, Acta Crystallogr A, Acta Crystallogr
Sect A, Acta Crystallogr A Cryst Phys Diffr Theor Gen
Crystallogr, Acta Crystallogr Sect A Cryst Phys Diffr
Theor Gen Crystallogr 2015, 71, 235–244.
20] L. Palatinus, C. A. Corrêa, G. Steciuk, D. Jacob, P.
Roussel, P. Boullay, M. Klementová, M. Gemmi, J.
Kopeček, M. C. Domeneghetti, F. Cámara, V.
Petříček, Acta Crystallogr B Struct Sci Cryst Eng
Mater 2015, 71, 740–751.
21] L. Palatinus, P. Brázda, M. Jelínek, J. Hrdá, G.
Steciuk, M. Klementová, Acta Crystallogr B Struct Sci
Cryst Eng Mater 2019, 75, 512–522.
[
[
22] L. Palatinus, G. Chapuis, J Appl Cryst 2007, 40, 786–
7
90.
23] “Crystallographic Computing System JANA2006:
General featuresꢀ: Zeitschrift für Kristallographie -
Crystalline Materials,” can be found under
https://www-degruyter-
com.inc.bib.cnrs.fr/view/j/zkri.2014.229.issue-5/zkri-
2
014-1737/zkri-2014-1737.xml, 2014.
24] P. Boullay, L. Palatinus, N. Barrier, Inorg Chem 2013,
2, 6127–6135.
[
[
5
25] K. Rickert, P. Boullay, S. Malo, V. Caignaert, K. R.
Poeppelmeier, INORG. CHEM. 2016, 55, 4403–4409.
5
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202006135
COMMUNICATION
Experimental Section
Synthesis
The Mn0.6Ni0.4As compound was synthesized using solid-state reaction. First, MnAs and NiAs binaries were synthesized from stoichiometric
amounts of elements Mn, Ni and As, weighed and crushed using agate mortar and pestle. Powders were introduced in alumina crucibles and
put into vacuum sealed quartz tubes. Latter were placed in a standing tube furnace and slowly heated up to 900°C (0.1°C/min) for a week.
Cooling down to room temperature was performed at a 1°C/min rate. Ternary compound was prepared weighing stoichiometric amounts of
MnAs and NiAs introduced in alumina crucibles, latter placed in quartz tubes, introduced in a standing furnace. Tube was slowly heated (1°C/mn)
up to 800°C, held at this temperature for 5 days and cooled to room temperature at the same rate. This process has been repeated three times
with intermediate crushings. Finally, the sample was annealed at 600°C for 1 month with the same heating and cooling rate.
Atomic imaging
High-Angle Annular Dark Field (HAADF) imagery imaging was performed on an ARM 200F with a corrected probe, operating at 200kV and
equipped with Centurio EDX spectrometer. The simulated ADF images have been calculated with the JEMS software considering the
convolution of the STEM probe with the intensity of the object (square of the projected potential multiplied by the electron-matter interaction
constant of the structure).
3D Electron Diffraction (3D ED)
A small quantity of Mn0.6Ni0.4As powder (<1 μg) was dispersed in a butanol solution and ground in an agate mortar. A drop of the suspension
was deposited and dried on a copper grid with a thin film of holey amorphous carbon. 3D ED experiment was performed with a JEOL 2010
transmission electron microscope (operating at 200 kV with a LaB
6
cathode) equipped with a Nanomegas DigiStar precession module and a
retractile side-entry Gatan ORIUS 200D CCD camera. PEDT data of non-oriented patterns were collected at room temperature. The precession
[
21]
angle was set to 1.2° with a goniometer tilt step below 1°. The PEDT data set was analyzed using the computer programs PETS2.0
,
[
22]
[23]
SUPERFLIP , and JANA2006. Details about the methodology to solve incommensurately modulated structures using PEDT can be found
[
12,24–26]
elsewhere
. For each data set, the result is a list of hklm indices with associated intensities and estimated standard deviations based on
counting statistics (Table 1).
Neutron Diffraction
Neutron powder diffraction (NPD) data has been collected at room temperature on D1B, ILL, France, using wavelength λ = 2.52 Å. About 5 g
[
23]
of the sample was put into a cylindrical vanadium can. Rietveld refinements were carried out in JANA2006. The Rietveld refinement resulted
in Rp = 0.0654, wRp = 0.0894, GOF = 0.0334 and R/wR (obs) all = 0.0571/0.0659 for N obs/all reflections = 41/44 (main: R/wR(obs)
0.0574/0.0571; order 1: R/wR(obs) = 0.0401/0.0501; order 2: R/wR(obs) = 0.1229/0.1171) (see refinement details in Table 1). Data are found
at http://doi.ill.fr/10.5291/ILL-DATA.DIR-172
6
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202006135
COMMUNICATION
In this paper, we unravel a structural feature that has remained unsolved for decades. We unveil an incommensurate
occupational modulation which creates a particular nanoscale ordering of MnAs and NiAs layers in the intermetallic
Mn0.60Ni0.40As solid solution phase. We have investigated this extraordinary phenomenon by state-of-the-art methodology; 3D
electron diffraction (PEDT), high-angle annular dark-field (HAADF) imaging, and neutron diffraction.
7
This article is protected by copyright. All rights reserved.