Phase relations and flux research for zinc oxide crystal growth in the ZnO-Na2O-P2O5 system

Article abstract of DOI:10.1016/j.jallcom.2007.10.112

The subsolidus phase relations of the ternary system ZnO-Na₂O-P₂O₅ were investigated by means of X-ray diffraction (XRD). There are 7 binary compounds, 4 ternary compounds and 16 three-phase regions in this system. The pha

Full text of DOI:10.1016/j.jallcom.2007.10.112

Journal of Alloys and Compounds 465 (2008) 436–441
Phase relations and flux research for zinc oxide crystal growth in the
ZnO–Na2O–P2O5 system
L.N. Jia, J.B. Lia, J. Luoa, J.K. Lianga,b,∗, J.Y. Zhanga, Y.H. Liua, G.H. Raoa
a Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
b International Center for Materials Physics, Academic Sinica, Shenyang 110016, China
Received 9 October 2007; received in revised form 23 October 2007; accepted 24 October 2007
Available online 4 November 2007
Abstract
The subsolidus phase relations of the ternary system ZnO–Na2O–P2O5 were investigated by means of X-ray diffraction (XRD). There
are 7 binary compounds, 4 ternary compounds and 16 three-phase regions in this system. The phase diagrams of the pseudo-binary sys-
tems of Na2Zn5(PO4)4–ZnO and NaPO3–ZnO were also investigated by means of XRD and differential thermal analysis (DTA) methods.
Na2Zn5(PO4)4–ZnO is an eutectic system with eutectic temperature about 872 ◦C. Only narrow composition range in the Na2Zn5(PO4)4–ZnO
system is suitable as flux to grow ZnO crystals. Two compounds, Na2ZnP2O7 and NaZnPO4, exist in the NaPO3–ZnO system. Two eutectic reac-
tions, Liquid-NaPO3 + Na2ZnP2O7 and Liquid-Na2ZnP2O7 + NaZnPO4, occur existing at about 590 ◦C and 777 ◦C, respectively. The NaZnPO4 is
formed by the peritectic reaction between liquid and ZnO at about 1007 ◦C. In the NaPO3–ZnO system, narrow composition range can be used as
flux for ZnO crystals growth below 1250 ◦C.
© 2007 Elsevier B.V. All rights reserved.
Keywords: ZnO–Na2O–P2O5 system; ZnO semiconductor; Phase diagrams; X-ray diffraction
1. Introduction
used as fluxes too, whereas the obtained ZnO were small nee-
dle crystals. Using the Group I A oxide as flux to grow ZnO
crystals, a p-type ZnO might be obtained by substituting the Zn
ion with the IA ion. Besides, the melting point of P2O5 is low
(about 580 ◦C), so it is significant to study the phase relations
of the ternary system ZnO–Na2O–P2O5 as a part of systemic
searching for a suitable flux to grow ZnO crystals.
Wurtzitic ZnO is a II–VI semiconductor with wide band gap
of 3.4 eV and large exciton binding energy of 60 meV. It has
excellent optical and electrical properties and important appli-
cations in many functional devices [1–4]. The main methods
for ZnO crystal growth are hydrothermal, vapor transport and
melt methods. The period of crystal growth by the hydrother-
mal method is long. The vapor transport method is not easy to
manipulate. The melt method, which can grow ZnO crystals at
atmospheric pressure with observable benefit, avoids the above
shortcomings. However, ZnO has high melting point of 1975 ◦C
and volatilizes seriously at high temperature. Therefore, a suit-
able flux for the melt method is desired to grow ZnO crystals at
a lower temperature. PbF2 was used as flux to grow ZnO crys-
tals, but it is noxious [5]. KOH [6] and KOH + NaOH [7] were
1.1. ZnO–P2O5 system
This system was investigated by Katnack and Hummel in
1958 [8]. Three compounds with the ZnO:P2O5 molar ratios of
3:1, 2:1 and 1:1 were obtained. Baez-Doelle [9] synthesized a
1:2 compound from the acidic melt of P2O5, H3PO4 and ZnO
at about 360 ◦C. Only the 3:1, 2:1 and 1:1 compounds were
obtained in our previous work [10].
1.2. Na2O–ZnO system
∗
Corresponding author at: Beijing National Laboratory for Condensed Matter
Four compounds were reported in this system with the
Na2O:ZnO molar ratios of 1:2, 1:1, 5:4 and 3:1 [11–15]. The
1:2 compound was prepared by heating the mixtures of the cor-
Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080,
China. Tel.: +86 10 82649084; fax: +86 10 82649531.
E-mail address: jkliang@aphy.iphy.ac.cn (J.K. Liang).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2007.10.112

L.N. Ji et al. / Journal of Alloys and Compounds 465 (2008) 436–441
437
responding binary oxides at 400–450 ◦C and the structure was
determined by single crystal XRD [11]. It crystallizes in the
monoclinic system with space group P21/c and lattice param◦-
crystallizes in the orthorhombic system with space group
P212121 and lattice parameters of a = 9.367(5), b = 5.390(2),
˚
c = 13.480(8) A [24].
˚
eters of a = 5.82(0), b = 5.95(2), c = 5.88(7) A and β = 117.6
The HT-Na3PO4 crystallizes in the cubic system with space
˚
[11]. Trinschek and Jansen [12] synthesized a new modifica-
tion of the 1:2 compound by solid-state reaction. According to
the single crystal structure determination, it crystallizes in the
tetragonal system with space group P43212 and lattice parame-
group F432 and lattice parameters a = 7.423 A [25]. Lissel [26]
reported that the room-temperature Na3PO4 belonged to the
¯
tetragonal systemwithspacegroup P421c andlatticeparameters
˚
of a = b = 10.8084(6), c = 6.8178(5) A. This phase undergoes a
ters of a = b = 6.1812(2), c = 9.4479(4) A. Trinschek and Jansen
transformation, which is complete by 300 ◦C, to a face-centred
cubic phase [26]. Belik [27] and Newsam [28] reported that the
˚
also synthesized the 1:1 compound [13] and the 5:4 compound
[14] by reacting Na2O, which was produced in situ from Na3N2
and NaNO2, with ZnO in the solid-state. According to the single
crystal structure determination, the 1:1 compound crystallizes
in the monoclinic system with space group P21/c and lattice
¯
HT-Na3PO4 belonged to the space group Fm3m with lattice
˚
˚
parameters of a = 7.424(1) A and a = 7.512(3) A, respectively.
˚
parameters of a = 7.7352(2), b = 5.9782(2), c = 5.7248(2) A and
1.4. ZnO–Na2O–P2O5 system
β = 94.934(3)◦. The 5:4 compound crystallizes in the rhombo-
¯
hedral system with space group R3m and lattice parameters
Seven compounds were reported in this system, i.e.
Na2ZnP2O7 [29–31], NaZn(PO3)3 [32–34], Na2ZnP4O12 [32],
NaZnPO4 [35,36], Na3ZnP3O10, [37] Na9Zn21(PO4)17 [38] and
Na9Zn3(PO4)5 [38].
◦
◦
˚
of a = b = 10.815(3), c = 17.930(7) A, α = β = 90 and γ = 120 .
Kastner and Hoppe [15] reported that the 3:1 compound
belonged to the hexagonal system with space group P63/mc and
˚
lattice parameters of a = b = 7.562, c = 5.859 A.
Na2ZnP2O7 crystals were obtained by slowly cooling
the molten stoichiometric mixtures of Na2CO3, ZnO and
(NH4)2HPO4 in Ref. [29]. It crystallizes in the tetragonal
system with space group P42/mnm and lattice parameters of
1.3. Na2O–P2O5 system
˚
Four compounds were reported in this system with the
Na2O:P2O5 molar ratios of 1:1, 5:3, 2:1 and 3:1.
a = b = 7.656(1), c = 10.233(2) A, Z = 4 [29]. Belharouak et al.
[30] also obtained the crystals of Na2ZnP2O7 and reported
The 1:1 compounds are sodium Kurrol salts. The crystal
structure of the type-A sodium Kurrol salt, a polyphosphate of
composition (NaPO3)x, was determined by Jost [16]. It crys-
tallizes in the monoclinic system with space group P21/n and
a large unit cell with space group P42/n and lattice parame-
ters aL = bL = 21.771(3), cL = 10.285(2) A, Z = 32 by taking into
˚
account of a great number of weak reflections. The relation
√
between the large and the small unit cell is that aL = 2 2aS,
cL = cS; hS = (hL − kL)/4, kS = (hL + kL)/4, lS = lL. Shepelev et
al. [31] reported that the space group of the Na2ZnP2O7 com-
pound was P42/mnm with lattice parameters a = b = 7.687(5),
˚
lattice parameters of a = 12.12(4), b = 6.20(2), c = 6.99(3) A and
β = 92.0(5)◦ [16]. McAdam et al. [17] refined the structure using
Jost’s data by the full-matrix least-squares program and obtained
the same results. Jost [18] also synthesized a new form of
sodium Kurrol salt (type-B), sodium meta-phosphate (NaPO3)n,
whose space group is P21/n with◦lattice parameters of a = 11.37,
˚
c = 10.275(7) A.
NaZn(PO3)3 compound was reported to have the cubic
¯
symmetry with space group I43 d and lattice parameter
¯
˚
˚
b = 6.01, c = 7.63 A and β = 85.7 [18]. Immirzi and Porzio [19]
a = 14.58 A [32], or with space group Pa3 and lattice param-
˚
refined the structure of the type-B compound, which was finely
ground using a micro-ball milling, and reported the space group
eter a = 14.2581(4) A [33]. While Aouad [34] reported that
it belonged to the orthorhombic system with space group
˚
I41/a with lattice parameters of a = b = 13.177(5), c = 5.940(3) A
Pbca and lattice parameters of a = 14.259(2), b = 14.234(3),
˚
˚
and a = b = 13.176(6), c = 5.931(3) A. Ondik [20] obtained the
c = 14.238(4) A.
(NaPO3)3 crystal by heating pure Na3P3O9·1.5H2O to about
650 ◦C and slowly cooling the melt at about 5–10 ◦C/h. It crys-
tallizes in the orthorhombic system with space group Pmcn and
The LT-NaZnPO4 was determined to have the mono-
clinic symmetry with the space group P21/n, but different
lattice parameters were reported: a = 8.656(3), b = 8.106(2),
◦
˚
˚
lattice parameters of a = 7.928(2), b = 13.214(3), c = 7.708(2) A.
c = 15.260(5) A, β = 89.80(3) in Ref. [35] ◦and a = 5.221(7),
˚
Two modifications of the 5:3 compound were reported, i.e.
the low-temperature phase (LT) and the high-temperature (HT)
phase. The crystal structure of the LT-Na5P3O10 was determined
by Davies and Corbridge in 1958 [21]. It crystallizes in the
monoclinic system with space group C2/c and lattice parame-
b = 10.019(2), c = 7.365(1) A, β = 90.25(1) in Ref. [36].
The HT-NaZnPO4 belonged to the hexagonal system with
space group P63 and lattice parameters of a = b = 5.101(3),
˚
c = 8.365(8) A [39]. The LT-NaZnPO4 underwent
a
reversible transformation to the HT-NaZnPO4 at about
ters of a = 16.00, b = 5.24, c = 11.25 A and β = 93 . Cruickshank
[22] refined the structure and obtained the same results. The
HT-Na5P3O10 crystallizes in the monoclinic system with space
group C2/c and lattice parameters of a = 9.61(3), b = 5.34(2),
887 ◦C [40].
◦
˚
Na2ZnP4O12 [32] and Na3ZnP3O10 [37] were only men-
tioned once. Only unindexed XRD patterns were reported for
Na9Zn3(PO4)5 [38]andNa9Zn21(PO4)17 [38]withoutanystruc-
tural data. According to our previous result [41], the composition
Na9Zn21(PO4)17 is the mixture of Na2Zn5(PO4)4 and NaZnPO4
phases.
◦
˚
c = 19.73(5) A, β = 112.0(5) [23].
Crystals of the 2:1 compound were grown from a melt
prepared from Na4P2O7·10H2O. At room temperature, it

438
L.N. Ji et al. / Journal of Alloys and Compounds 465 (2008) 436–441
lattice parameters of all the compounds observed in this work
were obtained using Chekcell program [42].
3.1.1. ZnO–P2O5 system
Three compounds with the ZnO:P2O5 molar ratios of 3:1, 2:1
and 1:1 were confirmed to exist in this system and indexed as
reported in our previous work [10].
3.1.2. ZnO–Na2O system
None of the reported compounds was observed in this work.
The phase identification of the sample with the Na2O:ZnO molar
ratio of 1:1 indicated that the sample was a mixture of ZnO and
Na2CO3 after sintered at 900 ◦C for 1 day. When the sample was
sintered at 900 ◦C for 3 days, the phase identification proved
that it was ZnO. This means that no compound formed in this
system in our experimental conditions, and this may be due to
the easy volatility of Na2O (decomposed from Na2CO3) at high
temperature.
Fig. 1. Subsolidus phase relations of the ZnO–Na2O–P2O5 system; (A)
Na2ZnP2O7; (B) NaZn(PO3)3; (C) NaZnPO4; (D) Na2Zn5(PO4)4; (E)
Zn3(PO4)2; (F) Zn2P2O7; (G) Zn(PO3)2; (H) NaPO3; (I) Na5P3O10; (J)
Na4P2O7; (K) Na3PO4; (ꢀ) three phases; (ꢀ) two phases; (᭹) single phase.
3.1.3. Na2O–P2O5 system
2. Experimental
The reported four compounds were all obtained in this work.
The result of the phase identification of this system was shown
in Fig. 1. The 1:1 compound belongs to the orthorhombic sys-
tem with space group Pmcn and lattice parameters a = 7.920(4),
Analytical grade ZnO, Na2CO3 and NH4H2PO4 were used to prepare the
specimens by solid-state reaction and quenching methods. While analytical
grade 5ZnO·2CO2·4H2O was used as source of ZnO in order to obtain the
pure NaZnPO4 compound. Altogether 68 specimens were prepared and their
compositions are shown in Fig. 1, among which there are 13 specimens for the
three binary subsystems and 55 specimens for the ternary system.
˚
b = 13.224(4), c = 7.703(7) A, which is in agreement with the
˚
results of a = 7.928(2), b = 13.214(3), c = 7.708(2) A in Ref. [20]
and different from those in Refs. [16–18,20]. The 5:3 compound
The powder in the nominal compositions of raw materials was mixed in an
agate mortar to get homogeneous. The mixtures of the samples containing less
P2O5 were preheated at 500 ◦C for 10 h with a slow heating rate, in order to avoid
the loss of components with the volatility of NH3, H2O and CO2. After being
pressed into pellets of 12 mm in diameter and 1–2 mm in thickness, samples
were sintered at different temperatures between 600 ◦C and 900 ◦C according to
different compositions and quenched at atmosphere. The sintered samples were
ground to powder and identified by XRD. Then the powder was pressed into
pellets again and sintered at the same temperature. The above procedure was
repeated until the XRD patterns showed no changes. The samples containing
more P2O5, of which the melting temperatures are low, were prepared by melting
the mixtures in a platinum crucible to get homogeneous. Glasses were obtained
by quenching the melts, and DTA was used to determine the crystallization and
melting temperatures of the glasses. For each sample, the glass was annealed at
a proper temperature between the crystallization and melting temperatures. The
samples were considered to be in equilibrium until the XRD patterns showed no
changes upon the successive heat treatment. The samples in the Na2O-rich area
are sintered at low temperatures to avoid the volatility of Na2O.
The XRD data were collected on an X-ray Rigaku diffractometer D/Max-
2500 with Cu K␣ radiation (45 kV × 250 mA) and a graphite monochromator
using continuous mode at a rate of 2θ = 4◦/min.
The XRD pattern for indexing was collected on an automated Pan Analyti-
cal X’pert MRD (45 kV × 40 mA) high-resolution diffractometer with Cu K␣1
radiation using a X’Celerator Retroft Detector and a Ge (1 1 1) monochromator.
The thermal analyses were conducted on a RSZ type high temperature ␮-
DTA apparatus with Pt–PtRh thermocouples. Platinum crucibles were used as
vessels and reference substances. The heating and cooling rate is 10 ◦C/min and
the highest temperature of the DTA measurement is 1250 ◦C.
belongs to the monoclinic system with space group C2/c and
˚
lattice parameters a = 9.612(1), b = 5.336(0), c = 19.692(4) A,
β = 111.9(5)◦, in agreement with the results of a = 9.61(3),
◦
˚
b = 5.34(2), c = 19.73(5) A, β = 112.0(5) in Ref. [23] and dif-
ferent from those in Refs. [21,22]. The 2:1 compound belongs
to the orthorhombic system with space group P212121 and
˚
lattice parameters a = 9.396(3), b = 5.389(5), c = 13.523(6) A,
in agreement with the result of a = 9.367(5), b = 5.390(2),
˚
c = 13.480(8) A in Ref. [24]. The 3:1 compound belongs to the
¯
tetragonal system with space group P421c and lattice parame-
˚
ters a = b = 10.829(7), c = 6.834(3) A, which is in agreement with
˚
the results of a = b = 10.8084(6), c = 6.8178(5) A in Ref. [26] and
different from those in Refs. [25,27,28].
The above results and the literature reports show the diver-
sity of the phosphate structures. The formation free energies
among the phases may be compatible, which result in the differ-
ent phases for different synthetic conditions and the existence
of complex phase transitions or metastable phases.
3.2. ZnO–Na2O–P2O5 system
3.2.1. Ternary compounds
Four ternary compounds were obtained in our synthetic con-
ditions. A new compound with chemical formula Na2Zn5(PO4)4
was successfully synthesized in this work. The Na9Zn21(PO4)17
reported in Ref. [38] was found to be the mixture of
4Na2Zn5(PO4)4 and NaZnPO4. The powder diffraction data of
the Na2Zn5(PO4)4 compound with Cu K␣ 2θ > 40◦ was listed
in Table 1, which can be used as a standard for phase analysis.
The figures of merit of indexing by DICVOL program [43] were
3. Results and discussions
3.1. Binary systems
The phase relations of the three binary systems ZnO–P2O5,
ZnO–Na2O and Na2O–P2O5 were first investigated. The refined

L.N. Ji et al. / Journal of Alloys and Compounds 465 (2008) 436–441
439
Table 1
Except for the above four mentioned ternary compounds, the
compounds with nominal compositions of Na9Zn3(PO4)5 and
Na2ZnP4O12, reported respectively by Refs. [38,32] were not
obtained in our work. The phase identification of the nominal
composition Na9Zn3(PO4)5 and Na2ZnP4O12 revealed that they
were mixtures of 3NaZnPO4 and 2Na3PO4, and NaZn(PO3)3
and NaPO3, respectively.
The interplaner distances and intensities of Na2Zn5(PO4)4 compound
h k l
dobs
dcal
Iobs
Ical
0 0 2
1 1 0
1 1 1
1 1 2
2 0 2
2 1 1
020, 113
004, 021
0 2 2
1 1 4
0 2 3
2 2 1
1 2 3
3 1 1
2 1 4
3 1 2
024, 115
1 2 4
8.248
6.566
6.100
5.142
4.392
4.275
4.243
4.134
3.779
3.501
3.365
3.224
3.202
3.144
3.023
2.987
2.963
2.849
2.824
2.758
2.665
2.611
2.595
2.574
2.543
2.532
2.475
2.458
2.377
2.342
2.314
2.280
2.264
8.284
6.580
6.115
5.152
4.398
4.281
4.254, 4.230
4.142, 4.120
3.784
3.505
3.370
3.227
3.205
3.147
3.026
2.989
2.968, 2.959
2.853
21.4
27.5
7.7
13.5
7.3
26.3
100
10.2, 7.5
12.7, 2.5
35.2
6.8
4.2
4.3
2.2
20.7
39.8
2.6
17.0, 11.8
5.6
6.3
11.1
5.9
26.7
100
7.8
17.0
33.0
7.8
3.5
5.9
3.2.2. The subsolidus phase relations
The result of the phase identification of the 68 samples
obtained at different temperatures is shown in Fig. 1. There are
7 binary compounds, 4 ternary compounds and 16 three-phase
regions in this system. There is no solid solution region between
any binary or ternary compounds.
2.6
26.4
49.7
3.0
21.1
5.6
51.5
24.3
5.9
39.5
36.2
9.4
2.2
5.5
8.4
28.9
7.6
3.3. Phase diagrams for searching fluxes for ZnO crystal
growth
From Fig. 1, we know that the region ZnO–Na2O–
Na3PO4–NaZnPO4–Na2Zn5(PO4)4–Zn3(PO4)2 in the ZnO–
Na2O–P2O5 ternary system is suitable to search for fluxes to
grow ZnO crystals. There is no compound observed in the
Na2O–ZnO system in our work, which may be due to the easy
volatility of Na2O at high temperature, so Na2O is not the suit-
able flux. Na3PO4 is also not the suitable flux because it cannot
melt until the temperature up to 1250 ◦C. Our previous result
[10] showed that Zn3(PO4)2 was not a suitable flux due to nar-
row composition range for ZnO crystal growth. NaZnPO4 melts
incongruently at 1007 ◦C and Na2Zn5(PO4)4 has rather low
melting point of 888 ◦C. So the pseudo-binary phase diagrams
of Na2Zn5(PO4)4–ZnO and NaZnPO4–ZnO were investigated.
2 2 3
2.827
46.8
313, 006, 130
106, 215, 321
0 2 5
132, 400
224
1 1 6
314, 125
4 0 2
231, 411
232, 412
2 1 6
0 2 6
1 3 4
2.772, 2.761, 2.736
2.669, 2.654, 2.650
2.614
2.598, 2.595
2.576
2.546
2.535, 2.535
2.477
2.461, 2.455
2.383, 2.378
2.343
2.316
2.283
2.5, 18.1, 2.1
5.1, 6.5, 1.6
33.0
6.6, 19.9
6.9
2.0
4.1, 1.1
6.0
25.0, 5.0
1.3, 6.9
8.1
4.0
4.2
10.2
5.9
4.6
233, 413, 126
2.269, 2.264, 2.260
5.1
1.6, 3.8, 1.8
The Iobs < 1.0 and Cu K␣ 2θ > 40◦are not shown in the table; Ical are obtained
3.3.1. Na2Zn5(PO4)4–ZnO system
by using the structural parameters from Ref. [41].
Na2Zn5(PO4)4 was prepared and used as starting material.
Eight samples were prepared in this system for different ZnO
content from 0 mol% to 70 mol%. After repeatedly sintering at
800 ◦C for 3 days to reach the equilibrium state, samples were
investigated by DTA and XRD. The results are listed in Table 2
and the phase diagram is constructed and shown in Fig. 2.
Na2Zn5(PO4)4 and ZnO form an eutectic system with the
eutectic temperature about 872 ◦C and the eutectic point at about
17 mol% ZnO. The dashed line denotes the predicted liquidus
which were not observed due to the temperature limit of 1250 ◦C
for our ␮-DTA apparatus. ZnO crystals can be obtained in the
M(20) = 58.1, F(20) = 109.2 (0.0035, 53), F(54) = 96.9 (0.0032,
176). Na2Zn5(PO4)4 crystallizes in the orthorhombic system
with space group Pbcn and lattice parameters of a = 10.381(2),
˚
b = 8.507(1), c = 16.568(3) A [41].
The space group of the Na2ZnP2O7 compound is P42/mnm
˚
with lattice parameters of a = b = 7.684(7), c = 10.264(0) A,
which is consistent with the results of a = b = 7.687(5),
˚
c = 10.275(7) A in Ref. [31]. The weak diffraction peaks
of the reported large unit cell were not observed in this
work.
The lattice parameters of the NaZn(PO3)3 compound are
a = 14.306(3), b = 14.277(0), c = 14.264(1) A with space group
Table 2
˚
Result of DTA measurements for the pseudo-binary system Na2Zn5(PO4)4–ZnO
Pbca, which are consistent with the result a = 14.259(2),
b = 14.234(3), c = 14.238(4) A in Ref. [34]. The space group of
No. Na2Zn5(PO4)4 Phase
(D) (mol%)
Eutectic temperature Melting
˚
(◦C)
temperature (◦C)
¯
¯
the NaZn(PO3)3 compound was reported as I43d and Pa3 in
Refs. [29,30], respectively. The reported disagreement may be
due to the different resolution of XRD patterns.
1
2
3
4
5
6
7
8
100
90
80
70
60
50
40
30
D
870
888
881
D + ZnO 874
D + ZnO 873
D + ZnO 876
D + ZnO 870
D + ZnO 871
D + ZnO 872
D + ZnO
1001
The space group of the NaZnPO4 compound is P21/n with
>1250
>1250
>1250
>1250
>1250
˚
lattice parameters a = 8.700(5), b = 8.156(8), c = 15.298(5) A,
β = 89.87(4)◦, which is consistent with a = 8.656(3),
◦
˚
b = 8.106(2), c = 15.260(5) A, β = 89.80(3) in Ref. [35]
and different from Ref. [36].

440
L.N. Ji et al. / Journal of Alloys and Compounds 465 (2008) 436–441
Fig. 2. Phase diagram of the Na2Zn5(PO4)4–ZnO pseudo-binary system.
Fig. 3. DTA plot of the sample NaZnPO4. Heating and cooling rate 10 ◦C/min.
region (about 17–25 mol% ZnO) in this system when the melt
cools. However, the region was so narrow that Na2Zn5(PO4)4 is
not a good flux to grow ZnO crystals.
3.3.2. NaPO3–ZnO system
NaZnPO4-ZnO pseudo-binary system is part of the NaPO3-
ZnO system, here we studied the NaPO3-ZnO phase diagram.
The DTA plot of the pure NaZnPO4 compound is shown in
Fig. 3. The cooling curve was moved a little along the exothermal
direction in order to observe the courses clearly. NaZnPO4 melts
incongruently at about 1110 ◦C. Fourteen compositions with dif-
ferent (0–70 mol%) ZnO contents were prepared by using ZnO
and NaPO3 as starting materials. NaPO3 was obtained by melt-
ing Na2CO3 and NH4H2PO4 at 800 ◦C, then annealing at 500 ◦C
for 2 days. The result of DTA and XRD analysis for the equilib-
rium samples is listed in Table 3 and the phase diagram is shown
in Fig. 4, which is different from Ref. [37]. The Na3ZnP3O10
compound was not obtained in our wok.
Fig. 4. Phase diagram of the NaPO3–ZnO pseudo-binary system.
tic system with the eutectic temperature of about 777 ◦C and
the eutectic point near 37 mol% ZnO. NaZnPO4 is the peritec-
tic resultant of Liquid and ZnO with the peritectic temperature
of about 1007 ◦C and peritectic point near 48 mol% ZnO. The
line with temperature of about 887 ◦C was corresponding to the
temperature of low- and high-temperature phase transition of
NaZnPO4. However, we did not obtain the high-temperature
Two compounds, Na2ZnP2O7 and NaZnPO4 exist in this
system. NaPO3 and Na2ZnP2O7 form an eutectic system with
the eutectic temperature of about 590 ◦C and the eutectic point
near 6 mol% ZnO. Na2ZnP2O7 and NaZnPO4 form an eutec-
Table 3
Result of DTA measurements for the pseudo-binary system NaPO3–ZnO
No.
ZnO (mol%)
Phasea
Eutectic
temperature (◦C)
Phase transition temperature
(◦C) of C
Peritectic temperature
(◦C)
Melting temperature
(◦C)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
5
H
628
H + A
H + A
H + A
H + A
A
A + C
A + C
A + C
C
C + ZnO
C + ZnO
C + ZnO
C + ZnO
ZnO
592
592
586
592
10
20
27
33.3
36
40
45
50
55
60
65
70
100
634
709
760
782
778
774
778
873
961
1100
>1250
>1250
>1250
>1250
1975
888
883
888
890
888
887
1007
1007
1006
1006
1007
aA, Na2ZnP2O7, C, NaZnPO4, H, NaPO3.

L.N. Ji et al. / Journal of Alloys and Compounds 465 (2008) 436–441
441
phase by sintering the sample at 900 ◦C for 1 day then quench-
ing at atmosphere. For the NaZnPO4-ZnO system, the liquidus
temperature cannot be observed for all the samples containing
ZnO due to the temperature limit of 1250 ◦C for our ␮-DTA
apparatus, so NaZnPO4 is not a good flux to grow ZnO crystals.
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4. Conclusions
ThephaserelationsweredeterminedintheZnO–Na2O–P2O5
ternary system, which contains 16 three-phase regions. There are
7 binary compounds and 4 ternary compounds in this system.
No solid solution region is formed between any binary or ternary
compounds. The phase diagrams of the Na2Zn5(PO4)4–ZnO
and NaPO3–ZnO systems were studied. Na2Zn5(PO4)4–ZnO is
the eutectic system with eutectic temperature about 872 ◦C and
there is only very narrow range suitable to grow ZnO crystals.
NaZnPO4 is the peritectic resultant of liquid and ZnO with peri-
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for ZnO crystals growth.
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This work was financially supported by the National Natural
Science Foundation of China (No. 50672123).
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