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Chemistry Letters 2001
Flux Growth of Single Crystals of BaBPO5
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Shilie Pan,* Yicheng Wu, Peizhen Fu, Guofu Wang, Guochun Zhang, Zhihua Li, and Chuangtian Chen
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
Beijing Center for Crystal Research and Development, Chinese Academy of Sciences, Beijing 100080, P. R. China
†
(Received March 22, 2001; CL-010257)
The powder barium borophosphate BaBPO was synthe-
growth depends to a large extent on whether an appropriate flux
can be found. For this reason, efforts have been made to search
for the best flux to suit the growth of BaBPO5 crystals.
According to the choice rules of fluxes, if a surplus of con-
stituents of the compounds can act as the flux for the growth of
the crystals of that compound, it will be possible to prevent the
flux from contaminating the grown crystal. The crystals grown
in such a melt will be of high purity and of good quality. So
several self-fluxes were firstly investigated for growing
BaBPO , such as BaCO , H BO , and NH H PO . The results
5
sized by solid-state reaction techniques. Single crystals BaBPO5
with sizes up to 20 mm × 15 mm × 10 mm were grown by top-
seeded solution growth method using H BO –NH H PO as
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fluxes. The crystals and the components volatilized were char-
acterized by the method of X-ray powder diffraction.
In the last forty years the first few compounds combining
both borate and phosphate groups were synthesized and struc-
turally characterized. High-temperature syntheses have pro-
duced handful of metal borophosphates. These are the follow-
5
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4
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4
indicate that H BO –NH H PO flux system is more suitable
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than others. Several ratios of BaCO : H BO : NH H PO were
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ing: MBPO , where M= Ca, Sr, or Ba, M BP O , where
tested for growing BaBPO crystals. Taking a wider crystal-
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,5
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M=Ba or Pb, Na B P O , Co BP O , M BPO , where
lization zone and higher crystal yield into account, the suitable
molar ratios of BaCO : H BO : NH H PO for the growth of
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5
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M=Mg, or Zn.8 The main structural features in them is that
boron is trigonally or tetrahedrally coordinated by oxygen, and
that the BO or BO and PO tetrahedra share corners and build
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BaBPO crystals turned out to be 1:1.8:1.8. The growth tem-
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perature decreased with decreasing of solute concentration, and
the growth temperature at 840–915 °C proved suitable for the
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infinite chains or networks. Therefore, the considerable variety
in crystal structure of borophosphate compounds provides a
great deal objects for the study aiming at exploring new func-
tional materials.
growth of BaBPO in our experiment.
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At the beginning of our experiment, BaBPO seeds were
5
unavailable. Therefore our first seed was a Pt wire seed, the
1
The compound BaBPO was first prepared by Bauer, who
raw materials were polycrystalline form BaBPO powder, ana-
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5
defined the chemical formula as 2BaO·B O ·P O . X-ray pow-
lytical grade H BO , and NH H PO . The charges were
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5
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1
der diffraction data of this compound was reported, and the
weighed in the appropriate ratio, ground, mixed thoroughly, and
then a platinum crucible of 40 mm in height and 40 mm in
diameter containing the crystal growth charge was mounted in a
vertical, temperature programmable furnace. When the initial
charge was melted in the platinum crucible, new portions of the
starting material were added until the proper amount of melt
was made. The crucible position was fixed at the center of the
furnace. We then dipped a platinum wire into the solution, the
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structure of BaBPO was also analyzed from powder data.
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To our knowledge, all these investigations were performed on
the powder of BaBPO and never on single crystals. The pres-
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ent paper reports the growth of BaBPO crystals from H BO -
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3
NH H PO flux using the top-seeded solution growth method.
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In this work, polycrystalline samples of BaBPO were pre-
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pared by using solid-state reaction techniques. The initial sub-
stances were analytical grade BaCO , H BO , and NH H PO .
solution was slowly cooled, and then the BaBPO crystals were
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The starting materials in the stoichiometric proportion were
mixed homogeneously in an agate mortar, and then packed into
a platinum crucible. The temperature was raised to 500 °C at a
rate of 2 °C /min in order to avoid ejection of powdered raw
material from the crucible due to vigorous evolution of CO2,
NH and decomposition of H BO . After preheating at 500 °C
obtained. Most of the crystals were cracked, but parts of new
crystals were usable as seeds.
A spontaneous growth method was performed in this early
stage; however, in order to obtain larger crystals BaBPO , the
5
main efforts have been focused on top-seeded solution growth
method. The experiment processing is as follows: A platinum
crucible containing the crystal growth charge was put into the
furnace. Then the furnace was sealed with a cover that had a
hole for insertion of the seed. The furnace was heated rapidly
to a temperature of 1050 °C and maintained at this temperature
for 24 h. Then it was cooled rapidly to 920 °C. A seed crystal
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for 10 h in a muffle furnace, the products were cooled to room
temperature, and ground up again; the mixture was heated at
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00 °C for 24 h, and then cooled to room temperature. The
purity of sample was checked by X-ray powder diffraction. A
single-phase powder of BaBPO was obtained when repeated
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heat treatment caused no further changes in the X-ray powder
diffraction. The solid products were then pulverized, and
ground into fine powder. The chemical equation can be
expressed as follows:
of BaBPO attached to a platinum rod was inserted slowly into
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the crucible and kept in contact with the surface of the solution,
while a temperature of 920 °C was maintained for half an hour
to dissolve the outer surface of the seed. The growing crystal
was rotated at a rate of 20 rpm. The solution was then cooled
rapidly to the saturation temperature of 915 °C determined by
repeated seeding, and then the temperature was slowly reduced
to 840 °C at a rate of 1 °C /day until the end of the growth. The
4
Since BaBPO melts incongruently, the flux method is
5
necessary for the purpose of its crystal growth. The success of
Copyright © 2001 The Chemical Society of Japan
Pan, Shilie
