Photon Factory Activity Report 2017 #35 (2018)

BL-10A/ 2016G520

Single crystal X-ray diffraction study of Ca2NaCd2V3O12 garnet
Akira YOSHIASA1*, Makoto Tokuda1, Hidetomo HONGU1, Tsutomu Mashimo1, Kazuake Iishi2
and Akihiko Nakatsuka2
1
Graduate School of Sciences and Technology, Kumamoto Univ. Kumamoto 860-8555, Japan
2
Graduate School of Sciences and Technology for Innovation, Yamaguchi Univ. 755-8611, Japan1 Introduction
A garnet structure has been investigated for not only
magnetic and optical properties but also the importance ascomponent material of the Earth’s mantle. The mean
formal valences of vanadate garnets are represented by(Ca2, Na)3+1.67M 2+2V3+5O12 (M = Mg, Mn, Co, Ni, Cu,Zn). The notable feature in vanadate garnets is that theV–O bond has a large covalency comparable to Si–O
bond in silicate garnets. It is expected that the repulsion
between cations across the shared edges of polyhedra in
vanadate garnet is different from that in YAG and YIG.
For understanding of the structural stability of garnets, inthis study, we first report the structural data of
Ca2NaCd2V3O12 and discuss its structural featurescompared with previous study of vanadate garnet [1].

dodecahedral shared edge length O4–O6 in Y= Mg, Zn,and Mn is considerably longer than the unshareddodecahedral edge length O4–O7. This feature comesfrom the weak repulsion between cations in X-site and Ysite. And also, the geometric constrains derived from thesize of Ca2+ and Na+ in X-site and M cations in Y-site
makes O4–O6 distance elongate anomalously. Thisgeometric constrain can be seen with in ugrandite garnets.
On the other hands, the shared dodecahedral edge O4–O6
distance in Y = Cd become shorter than the unsharededge O4–O7 distance, as shown in Fig. 1 This result issimilar to the tendency for pyralspite garnet. The O4-O7
distance maintain constant values against size of M
cations in Y-site [1].

2 Experiment
The single crystal of Ca2NaCd2V3O12 garnet wassynthesized using a floating zone method. The
characterization of synthesized crystal was examinedusing JEOL JCMA-733 electron microprobe analyzer.
The crystal was ground into a sphere 0.12 mm in diameterfor absorption correction. Single-crystal X-ray diffraction
measurements were carried out with a four-circle
diffractometer at the BL-10A beam line of the Photon
Factory, Tsukuba, Japan, using monochromatizedsynchrotron X-ray (λ = 0.70006 Å) radiation. The unitcell parameters at each temperature were determined by
the least-squares method from a set of 25 reflections.
During the least-square refinements a correction for
isotropic extinction was applied. After several cycles ofrefinements the displacement parameters were converted
from isotropic to an anisotropic model. Final R1and wR2
values were 0.0159 and 0.0199, respectively [2].
3 Results and Discussion
The effect of ionic radius of Y-site cation causes theincrease of cation–cation distances and finally theincrease of the lattice constant a. As one of features ofvanadate garnet, cation–cation distances are long ascompared with the one of silicate garnets. For vanadate
garnets, the ionic radius of cation in X-, Y-, and Z-site are
relatively larger and cations in X- and Y-site has lessvalence electrons as compared with that of other generalgarnets[1]. Therefore, it is thought that the repulsions of(Ca, Na)–(Ca, Na) and (Ca, Na)–Cd are fairly weaker
than the repulsions of X–X and X–Y of other garnets.
We consider the comparison of the vanadate garnet (Y= Cd) with other vanadate garnets (Y = Mg, Zn, and Mn).
The first structural feature is that the dodecahedral–

Fig. 1: The shared (open circles) and unshared (opensquares) oxygen–oxygen edge lengths plotted against theionic radii in the Y-site cation (Mg, Zn, Mn and Cd).
References[1] M. Tokuda, A. Yoshiasa, T. Mashimo, K. Iishi and A.
Nakatsuka, Acta Crystallographica Section C74 (2018),
460-464 https://doi.org/10.1107/S2053229618003741* yoshiasa@sci.kumamoto-u.ac.jp