ISSN 0020-1685, Inorganic Materials, 2018, Vol. 54, No. 6, pp. 591–595. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © D.O. Savinykh, S.A. Khainakov, A.I. Orlova, S. Garcia-Granda, 2018, published in Neorganicheskie Materialy, 2018, Vol. 54, No. 6, pp. 622–627.
Preparation and Thermal Expansion of Calcium Iron Zirconium
Phosphates with the NaZr
D. O. Savinykh
*, S. A. Khainakov
, A. I. Orlova
, and S. Garcia-Granda
Lobachevsky State University, pr. Gagarina 23, Nizhny Novgorod, 603950 Russia
University of Oviedo, Calle San Francisco 1, 33003, Oviedo, Spain
Received August 14, 2017; in final form, November 27, 2017
0.5(1 + x)
phosphates have been synthesized by a sol–gel process. The individual
compounds and solid solutions obtained crystallize in the NaZr
structure (trigonal symmetry, sp. gr.
R ). Using high-temperature X-ray diffraction, we have determined their thermal expansion parameters in
the temperature range from 25 to 800°C. With increasing x, the magnitudes of their linear thermal expansion
coefficients and thermal expansion anisotropy decrease. Most of the synthesized phosphates can be rated as
low-thermal-expansion compounds and can be regarded as materials capable of withstanding thermal
Keywords: NZP, phosphate, sol–gel process, X-ray diffraction, solid solution, thermal expansion
Owing to the wide isomorphism characteristic of
(NZP) structure [1–3], structural
analogs of NZP are of interest for designing new inor-
ganic materials for a variety of purposes: radioactive
waste consolidation [4, 5], minor actinide trans-
mutation [6, 7], thermally stable ceramics [8, 9], ionic
conductors [10, 11], phosphors [12, 13], and other
Such compounds have a framework structure and
can be described by the general crystal-chemical for-
]. Their structural frame-
work is made up of TO
octahedra and XO
which share oxygens. The blocks linked in this manner
have the form of helical ribbons running along the
crystallographic axis c. The framework contains M1
and M2 voids, differing in size, which are capable of
accommodating a wide variety of cations compensat-
ing its charge [2, 3].
Various iso- and heterovalent substitutions allow
one to control the properties of the resulting com-
pounds, making them respond in the desired manner.
One such property is the thermal expansion of materi-
als. A crystal-chemical approach makes it possible to
create materials of particular compositions with low
and controlled thermal expansion, which are capable
of withstanding thermal “stress” and combining with
other materials without additional deformation.
Most studies concerned with the high-temperature
crystal chemistry of NZP-type orthophosphates deal
with double phosphates containing tetravalent ele-
ments on the T site of the framework and alkali-metal
or alkaline-earth cations on the M sites.
In the AZr
 and AHf
 (A =
Na, K, Rb, Cs) series, the magnitudes of the thermal
expansion and anisotropy coefficients decrease as the
ionic radius of the alkali metal cation increases in
going form Na to Cs; that is, the cesium-containing
orthophosphates have the smallest thermal expansion
coefficients (TECs) and lowest anisotropy .
In the B
(B = Mg, Ca, Sr, Ba) zirco-
nium phosphates, containing the doubly charged cat-
ions on the M1 site, increasing the size of the B
ion leads to a change in the sign of their thermal
expansion coefficients. In particular, the calcium-
containing phosphates have thermal expansion coeffi-
< 0 and α
> 0, whereas the strontium- and bar-
ium-containing phosphates have α
> 0 and α
< 0 .
In the Na
0.5 + x
1.5 – x
(R = Al, Fe) sys-
tems, the magnitude of the linear thermal expansion
coefficient was shown to decrease with decreasing M-
site occupancy .
Many of the NZP-type phosphates have low ther-
mal expansion [8, 9, 14–19]. This can be accounted
for in terms of the unique behavior of their structure
on heating: expansion and compression in different
crystallographic directions . In designing materi-
als stable to thermal “stress,” not only a small average
thermal expansion coefficient but also low thermal
expansion anisotropy are important.