X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering
A few samples of nanocrystalline TiN–TiB₂ ceramics were synthesized by high-pressure (3.0 GPa) and high-temperature (t = 1300–1500°C) sintering a mixture of TiN and TiB₂ nanopowders (80 wt.% TiN and 20 wt.% TiB₂) and the microhardness of the samples was determined. Peculiarities of the chemical bond...
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| Zitieren: | X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering / A.I. Bykov, I.I. Timofeeva, A.V. Kovalev, L.P. Isayeva, A.V. Ragulya, Ya.V. Zaulychny, O.Yu. Khyzhun // Физика и техника высоких давлений. — 2007. — Т. 17, № 1. — С. 32-41. — Бібліогр.: 25 назв. — англ. |
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irk-123456789-702872014-11-03T03:01:40Z X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering Bykov, A.I. Timofeeva, I.I. Kovalev, A.V. Isayeva, L.P. Ragulya, A.V. Zaulychny, Ya.V. Khyzhun, O.Yu. A few samples of nanocrystalline TiN–TiB₂ ceramics were synthesized by high-pressure (3.0 GPa) and high-temperature (t = 1300–1500°C) sintering a mixture of TiN and TiB₂ nanopowders (80 wt.% TiN and 20 wt.% TiB₂) and the microhardness of the samples was determined. Peculiarities of the chemical bonding of the TiN–TiB₂ ceramics possessing the highest microhardness among the samples under consideration, mainly 29.65 ± 0.90 GPa, were studied in the present work using the X-ray emission and photoelectron spectroscopy methods. The X-ray emission spectra reflecting the energy distribution of the valence electronic states of the constituents (the N Kα (N 2p-like states), B Kα (В 2p-like states), Ti Lα (valence Ti s,d-like states) and Ti Kβ₅ (Ti 4p-like states) bands) were measured for the mentioned ceramics and for the initial mixture of TiN and TiB₂ nanopowders. For the above substances the X-ray photoelectron core-level binding energies were evaluated as well. It has been established that, when synthesizing the nanocrystalline TiN–TiB₂ ceramics from the initial mixture of TiN and TiB₂ nanopowders, the half-widths of the X-ray emission Ti Lα and Ti Kβ₅ bands decrease by (0.5–0.6) ± 0.2 eV. 2007 Article X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering / A.I. Bykov, I.I. Timofeeva, A.V. Kovalev, L.P. Isayeva, A.V. Ragulya, Ya.V. Zaulychny, O.Yu. Khyzhun // Физика и техника высоких давлений. — 2007. — Т. 17, № 1. — С. 32-41. — Бібліогр.: 25 назв. — англ. 0868-5924 PACS: 78.70.Dm, 78.70.En, 79.60.−i, 82.80.Ej, 82.80.Pv http://dspace.nbuv.gov.ua/handle/123456789/70287 en Физика и техника высоких давлений Донецький фізико-технічний інститут ім. О.О. Галкіна НАН України |
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A few samples of nanocrystalline TiN–TiB₂ ceramics were synthesized by high-pressure (3.0 GPa) and high-temperature (t = 1300–1500°C) sintering a mixture of TiN and TiB₂ nanopowders (80 wt.% TiN and 20 wt.% TiB₂) and the microhardness of the samples was determined. Peculiarities of the chemical bonding of the TiN–TiB₂ ceramics possessing the highest microhardness among the samples under consideration, mainly 29.65 ± 0.90 GPa, were studied in the present work using the X-ray emission and photoelectron spectroscopy methods. The X-ray emission spectra reflecting the energy distribution of the valence electronic states of the constituents (the N Kα (N 2p-like states), B Kα (В 2p-like states), Ti Lα (valence Ti s,d-like states) and Ti Kβ₅ (Ti 4p-like states) bands) were measured for the mentioned ceramics and for the initial mixture of TiN and TiB₂ nanopowders. For the above substances the X-ray photoelectron core-level binding energies were evaluated as well. It has been established that, when synthesizing the nanocrystalline TiN–TiB₂ ceramics from the initial mixture of TiN and TiB₂ nanopowders, the half-widths of the X-ray emission Ti Lα and Ti Kβ₅ bands decrease by (0.5–0.6) ± 0.2 eV. |
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Article |
| author |
Bykov, A.I. Timofeeva, I.I. Kovalev, A.V. Isayeva, L.P. Ragulya, A.V. Zaulychny, Ya.V. Khyzhun, O.Yu. |
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Bykov, A.I. Timofeeva, I.I. Kovalev, A.V. Isayeva, L.P. Ragulya, A.V. Zaulychny, Ya.V. Khyzhun, O.Yu. X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering Физика и техника высоких давлений |
| author_facet |
Bykov, A.I. Timofeeva, I.I. Kovalev, A.V. Isayeva, L.P. Ragulya, A.V. Zaulychny, Ya.V. Khyzhun, O.Yu. |
| author_sort |
Bykov, A.I. |
| title |
X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering |
| title_short |
X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering |
| title_full |
X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering |
| title_fullStr |
X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering |
| title_full_unstemmed |
X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering |
| title_sort |
x-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline tin and tib₂ after highpressure sintering |
| publisher |
Донецький фізико-технічний інститут ім. О.О. Галкіна НАН України |
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2007 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/70287 |
| citation_txt |
X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering / A.I. Bykov, I.I. Timofeeva, A.V. Kovalev, L.P. Isayeva, A.V. Ragulya, Ya.V. Zaulychny, O.Yu. Khyzhun // Физика и техника высоких давлений. — 2007. — Т. 17, № 1. — С. 32-41. — Бібліогр.: 25 назв. — англ. |
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Физика и техника высоких давлений |
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Физика и техника высоких давлений 2007, том 17, № 1
32
PACS: 78.70.Dm, 78.70.En, 79.60.−i, 82.80.Ej, 82.80.Pv
A.I. Bykov, I.I. Timofeeva, A.V. Kovalev, L.P. Isayeva, A.V. Ragulya,
Ya.V. Zaulychny, O.Yu. Khyzhun
X-RAY EMISSION AND PHOTOELECTRON SPECTROSCOPY
STUDIES OF INTERACTION OF NANOCRYSTALLINE TiN AND TiB2
AFTER HIGH-PRESSURE SINTERING
Institute for Problems of Materials Science, National Academy of Sciences of Ukraine
3 Krzhyzhanivsky str., UA-03142 Kyiv, Ukraine
A few samples of nanocrystalline TiN–TiB2 ceramics were synthesized by high-pressure
(3.0 GPa) and high-temperature (t = 1300–1500°C) sintering a mixture of TiN and TiB2
nanopowders (80 wt.% TiN and 20 wt.% TiB2) and the microhardness of the samples was
determined. Peculiarities of the chemical bonding of the TiN–TiB2 ceramics possessing
the highest microhardness among the samples under consideration, mainly 29.65 ± 0.90
GPa, were studied in the present work using the X-ray emission and photoelectron spec-
troscopy methods. The X-ray emission spectra reflecting the energy distribution of the
valence electronic states of the constituents (the N Kα (N 2p-like states), B Kα (В 2p-like
states), Ti Lα (valence Ti s,d-like states) and Ti Kβ5 (Ti 4p-like states) bands) were meas-
ured for the mentioned ceramics and for the initial mixture of TiN and TiB2 nanopowders.
For the above substances the X-ray photoelectron core-level binding energies were
evaluated as well. It has been established that, when synthesizing the nanocrystalline
TiN–TiB2 ceramics from the initial mixture of TiN and TiB2 nanopowders, the half-widths
of the X-ray emission Ti Lα and Ti Kβ5 bands decrease by (0.5–0.6) ± 0.2 eV.
1. Introduction
Transition metal (TM) borides and nitrides of group IVB of the Periodic Table
possess a unique combination of properties such as high melting point, hardness,
low electrical resistivity, high thermal conductivity, and chemical stability [1–4].
Therefore, the above compounds are of great interest both in science and in tech-
nology. The chemical bonding in TM borides and nitrides of group IVB of the Pe-
riodic Table is a superposition of the covalent, metallic and ionic components
[2,3]. As a result, the interpretation of the electronic structure of the compounds is
rather difficult [3,4].
Many of physical and chemical properties of the compounds can be predicted
and understood by considering their electronic structure. Due to the results of
band-structure calculations of TiN [3,5–12] and TiB2 [13–17] and of experimental
Физика и техника высоких давлений 2007, том 17, № 1
33
studies (using either X-ray emission, absorption or photoelectron spectroscopy
methods) of these compounds [2,12,18–20], the occupied part of the valence band
of titanium nitride and titanium diboride is determined mainly by the energy dis-
tribution of the Ti 3d-, Ti 4p- and N(B) 2p-like states. Additionally, for the above
compounds, charge transfer in the direction from titanium atoms to nitrogen (bo-
ron) atoms and a strong Ti 3d−N(B) 2p-hybridization are characteristic. The main
difference in the chemical bonding of the compounds is the existence of direct B–
B bonds in titanium diboride, while direct N–N bonds are absent in titanium
mononitride [1–4].
The purpose of this work is to investigate the character of chemical bonding in
a material obtained due to interaction of titanium mononitride with titanium di-
boride at high pressure–high temperature conditions. It is well known that TiN
crystallizes in a cubic structure of NaCl-type with lattice parameter a = 0.4244 nm,
however TiB2 in a hexagonal structure of AlB2-type with lattice parameters a =
= 0.3028 nm and c = 0.3228 nm [4,21]. For investigation of peculiarities of the
chemical bonding of a material obtained as a result of high pressure–high tem-
perature treatments of a mixture of TiN and TiB2 nanopowders, we have em-
ployed the X-ray emission spectroscopy and X-ray photoelectron spectroscopy
(XPS) methods.
2. Experimental
A mixture of ultra-fine plasmochemical powders (synthesized and certificated
by «Plasma & Ceramic Technologies» Ltd, Latvia) was chosen in the ratio 80
wt.% TiN and 20 wt.% TiB2 as a precursor for obtaining a series of nanocrystal-
line TiN–TiB2 ceramics. The powder sizes were found to be in the range 20 to 40
nm [22]. The synthesis of the ceramics was carried out in two stages. On the first
stage, the mentioned mixture of ultra-fine TiN and TiB2 powders was undergone
to high pressure (about 4 GPa, without
heating) for granulating. On the second
stage, the pressure was decreased to 3 GPa
and the granulated mixture of TiN and TiB2
was heated to 1300–1500°C for 1–5 min
in order to obtain TiN–TiB2 ceramics.
Sintering conditions for obtaining 14
samples of TiN–TiB2 ceramics are sum-
marized in Table 1. As one can see from
data listed in Table 1, the microhardness
of the TiN–TiB2 ceramics obtained due
to the above-mentioned high pressure-
high temperature treatments is within
17.48–29.65 GPa. It is well known that
the hardness of solids is determined by
peculiarities their chemical bonding.
Fig. 1. Data of X-ray diffraction analysis
of the pristine mixture of ultra-fine TiN
and TiB2 powders (1) and of the TK-4
ceramics obtained due to sintering the pow-
ders at 3.0 GPa and 1500oC for 3 min (2)
Физика и техника высоких давлений 2007, том 17, № 1
34
Therefore, for our experimental study of chemical interaction of atoms in the
TiN–TiB2 ceramics, we have chosen the one possessing the highest microhardness
among those obtained in the present high pressure–high temperature sintering,
mainly the TK-4 ceramics (see Table 1). Due to the X-ray diffraction analysis car-
ried out with a DRON-3 diffractometer using Cu Kα radiation (Fig. 1), the TK-4
ceramics consists of two phases, mainly titanium mononitride, TiN, with a lattice con-
stant а = 0.4245 nm and titanium diboride, TiB2, with lattice constants а = 0.3025 nm
and с = 0.3230 nm. The above unit-cell parameters of the TK-4 ceramics differ
slightly from those of the initial powder mixture: TiN (а = 0.4242 nm) and TiB2
(а = 0.3029 nm and с = 0.3236 nm). Microscopy studies of the TK-4 ceramics
have revealed that its grain sizes are within 90 to 120 nm [23].
Table 1
Sintering conditions and microhardness of nanocrystalline ceramics obtained due to
high pressure–high temperature treatments of the ultra-fine TiN–TiB2 powders
Sintering conditionsSpecimen pressure, GPa temperature, °C duration, min Microhardness, GPa
TK-1 3 1300 1 23.47 ± 1.00
TK-2 3 1400 3 24.93 ± 1.80
TK-3 3 1300 3 22.99 ± 1.20
TK-4 3 1500 3 29.65 ± 0.90
TK-5 3 1600 3 25.87 ± 1.40
TK-6 3 1300 3 25.30 ± 1.90
TK-7 3 1400 3 26.71 ± 0.50
TK-8 3 1500 3 27.98 ± 1.70
TK-9 3 1600 3 23.43 ± 0.80
TK-10 3 1300 1 25.40 ± 0.70
TK-11 3 1300 5 21.08 ± 1.00
TK-12 3 1300 5 20.89 ± 0.70
TK-13 3 1600 5 22.42 ± 1.30
TK-14 3 1600 5 17.48 ± 0.70
The ultrasoft X-ray emission N Kα and B Kα (K → LII,III transition) and Ti Lα
(LIII → MIV,V transition) bands reflecting the energy distribution of the N 2p-, B
2p- and valence Ti s,d-like states, respectively, in the studied mixture of the ultra-
fine TiN and TiB2 powders and in the nanosrystalline TK-4 ceramics derived by
high-temperature and high-pressure treatments of the powder mixture were ob-
tained using two RSM-500 spectrometers. The N Kα and Ti Lα emission bands
were derived using the RSM-500 spectrometer with a diffraction grating of 600
lines/mm and a radius of curvature R ≈ 6 m. In the RSM-500 spectrometer used in
the present work for studies of the B Kα band, the dispersion element was a dif-
fraction grating with 600 lines/mm and a radius of curvature R ≈ 2 m. In the both
spectrometers, the detectors were secondary electron multipliers VEU-6 with CsI
photocathodes. Operating conditions of X-ray tubes in the present experiments
were the following: accelerating voltage Ua = 4 kV and anode current Ia = 10 mA
Физика и техника высоких давлений 2007, том 17, № 1
35
when studying the B Kα bands and Ua = 5 kV and Ia = 11 mA when measuring
the N Kα and Ti Lα bands.
The fluorescent X-ray emission Ti Kβ5 bands (K → MIV,V transition), reflect-
ing the energy distribution of the valence Ti p-like states, in the ultra-fine TiN–
TiB2 powder mixture and in the TK-4 ceramics were derived using a DRS-2 spec-
trograph equipped with an X-ray BKhV-7 tube (chromium anode). The Ti Kβ5
bands were measured due to reflection from the (0001) plane of a quartz crystal
prepared according to Johann (see Ref. [20] for details). Operating conditions of
the BKhV-7 tube in the experiments were Ua = 35 kV and Ia = 70 mA.
The spectrometer/spectrograph energy resolutions were 0.2 eV in the case of
measuring the B Kα band, about 0.3 eV in the energy regions corresponding to the
positions of the N Kα and Ti Lα bands, and better than 0.4 eV in the case of
measuring the Ti Kβ5 bands.
Measurements of the XPS core-level spectra were carried out in an ion-
pumped chamber of an ES-2401 spectrometer having a base pressure less than
5·10−8 Pa. In the mentioned spectrometer, the Mg Kα radiation (E = 1253.6 eV)
was used as a source of spectra excitation. The binding energy (BE) of 84.00 ±
0.05 eV of the XPS Au 4f7/2 core-level spectrum was used as a reference.
3. Results and discussion
In titanium diboride, TiB2, with the structure of AlB2-type, boron atoms can be
viewed as those inserted into interstitials of the hexagonal lattice formed by tita-
nium atoms [4]. Therefore, similar to TiN, a typical representative of the class of
interstitial phases, titanium diboride can be also considered as a representative of
such phases. Additionally, the similarity exists in chemical interaction of titanium
atoms with boron and nitrogen atoms in TiB2 and TiN, respectively. As Sere-
bryakova and co-workers stress [4], when synthesizing titanium borides the
charge transfer occurs from titanium atoms to boron atoms and the B sp2- and B
sp3-like hybridization with the valence Ti s,d-like states takes place. The similar
effect is characteristic of titanium nitrides, however the N sp3- and N s2p6-like hy-
bridization with the metallic valence s,d-like states is characteristic of this com-
pound. Certainly, when sintering titanium diboride and titanium nitride one could
expect the formation of a TiB2–TiN solid solution. Nevertheless, it is well known
that interaction of TiB2 and TiN phases is rather difficult [4,24]. Due to studies of
interaction of titanium diboride and titanium nitride made by Huang and Chen
[25], the formation of a TiN layer on a TiB2 surface was observed at 1400°C,
however after 11 hour exposing at the mentioned temperature, in addition to TiN,
boron nitride was also synthesized. Nevertheless, changes of lattice parameters of
TiB2 during its nitriding were not studied in Ref. [25]. It is believed that, in nano-
crystalline states of TiB2 and TiN phases their interaction will increase because of
increasing defection and the surface energy of the phases in such a state [22]. Ad-
ditionally, high pressure and temperature that increase lattice energy should assist
this interaction. Such treatment was employed in the present work as it has been
Физика и техника высоких давлений 2007, том 17, № 1
36
mentioned in the Experimental section.
The presence of the interaction should be
visible upon changes of shapes of the X-
ray emission bands reflecting the energy
distribution of the valence electronic
states of the ceramic constituents and
pristine mixture of the ultra-fine TiB2
and TiN powders.
Fig. 2 shows results of measurements
of the Ti Lα emission bands in the two
specimens under study, initial mixture of
TiB2 and TiN powders and obtained from
the mixture at high pressure–high tem-
perature conditions the nanocrystalline
TK-4 ceramics. The band of pure metallic
titanium, for comparison, is also pre-
sented there. From Fig. 2 it is apparent
that the two-peak structure (features «a»
and «b») is characteristic of the Ti Lα
bands of the pristine mixture of ultra-fine TiN and TiB2 powders and of TK-4 ce-
ramics, while only one feature «a» is typical of the band of pure metallic titanium
(there are, certainly, a few additional features slightly resolved on the bands of the
ceramics and the initial mixture of ultra-fine TiN and TiB2 powders). Due to the
results of experimental studies for the electronic structure of TiN and TiB2 com-
pounds summarized in monographs [2,4], the high-energy subband «b» of the Ti Lα
band is created by the Ti 3d-like states taking part in forming the metallic compo-
nent of the chemical bonding of the above compounds, while the low-energy feature
«a» of the band in titanium diboride and titanium mononitride is created by the Ti
3d-like states taking part in the formation of the covalent dTi−pB(N) bonds due to the
Ti 3d−B(N) 2p-like hybridization. The relative intensities of the «a» and «b» sub-
bands of the Ti Lα emission band do not change significantly when sintering the
pristine mixture of TiN and TiB2 powders at high pressure–high temperature condi-
tions and obtaining the TK-4 ceramics. However, the subband «b» of the Ti Lα
band in the pristine mixture of TiN and TiB2 powders is positioned by about 0.5 eV
towards higher photon energies as compared with that in the TK-4 ceramics. It is
obvious that the Ti Lα band of the pristine powder mixture is the superposition of
the bands of constituent substances, mainly ultra-fine TiN and TiB2 compounds. On
the contrary, the Ti Lα band of the TK-4 ceramics is the spectrum representing the
energy distribution mainly of the valence Ti s,d-like states in the solid. Therefore, as
data listed in Table 2 reveal, the half-width of the band decreases by about 0.6 eV
when going from the pristine mixture of ultra-fine TiN and TiB2 powders to the
TK-4 ceramics obtained due to high pressure–high temperature sintering the pow-
der mixture.
Fig. 2. X-Ray emission Ti Lα bands of
the pristine mixture of ultra-fine TiN and
TiB2 powders (1) and of the TK-4 ce-
ramics obtained due to sintering the
powders at 3.0 GPa and 1500°C for 3
min (2); for comparison, the band of pure
metallic titanium is also presented (3)
Физика и техника высоких давлений 2007, том 17, № 1
37
Table 2
Half-widths (in eV) of the X-ray emission bands of the pristine mixture
of ultra-fine TiN and TiB2 powders and of the TK-4 ceramics obtained
due to sintering the powders at 3.0 GPa and 1500°C for 3 min
Specimen B Kα band N Kα band* Ti Lα band Ti Kβ5 band**
Pristine mixture of ultra-
fine TiN and TiB2 powders 4.5 3.3 8.7 7.0
Nanocrystalline TiN–TiB2
(TK-4) ceramics 4.3 3.2 8.1 6.5
Uncertainty ±0.2 ±0.2 ±0.2 ±0.2
*The band superimposes the inner X-ray Ti Ll line.
**Without any corrections for tails of the inner X-ray Ti Kβ1,3 line superimposing the band.
The above results for the Ti Lα band look to be in excellent agreement with
those obtained when studying the Ti Kβ5 band for the substances under consid-
eration. Results of investigation of the Ti Kβ5 bands in the pristine mixture of
TiB2 and TiN powders, the nanocrystalline TK-4 ceramics obtained from the
mixture at high pressure–high temperature conditions and, for comparison, in pure
metallic titanium are presented in Fig. 3. As Fig. 3 reveals, the main maxima «a»
of the Ti Kβ5 bands in the mixture of TiB2 and TiN powders and in the TK-4 ce-
ramics are positioned by 3.8 ± 0.2 eV
towards lower photon energies as com-
pared with that of the band of pure me-
tallic titanium. In accordance with the
above results for the Ti Lα band, the
main maximum «a» of the Ti Kβ5 band
in titanium nitrides and borides is cre-
ated by the Ti 4p-like states hybridized
with the N(B) 2p-like states, while the
high-energy feature «b», which is re-
solved on the spectrum of the TK-4 ce-
ramics, is formed by the Ti 4p-like states
taking part in the formation of the me-
tallic Ti–Ti bonds in the TiB2 and TiN
compounds [2,4]. It is obvious that the
energy position of the maximum «a» of
the Ti Kβ5 band does not change when
going from the pristine mixture of TiN
and TiB2 powders to the TK-4 ceramics.
However, the half-width of the Ti Kβ5
band is higher by about 0.5 eV in the
initial mixture of ultra-fine TiN and TiB2
powders as compared with that in the
Fig. 3. X-Ray emission Ti Kβ5 bands of
the pristine mixture of ultra-fine TiN and
TiB2 powders (1) and of the TK-4 ce-
ramics obtained due to sintering the
powders at 3.0 GPa and 1500°C for 3
min (2); for comparison, the band of pure
metallic titanium is also presented (3)
Физика и техника высоких давлений 2007, том 17, № 1
38
TK-4 ceramics studied (Table 2). Taking into account the same arguments as in
the case for the Ti Lα band, the above-mentioned decreasing the half-width of the
Ti Kβ5 band can be explained by the fact that the band of the pristine powder
mixture represents the superposition of the bands of constituent compounds (TiN
and TiB2), while the band of the TK-4 ceramics is the spectrum representing the
energy distribution of the Ti 4p-like states of a TiN–TiB2 solid.
The investigation of the N Kα bands in the initial mixture of ultra-fine TiN
and TiB2 powders and the TK-4 ceramics obtained from the powders after their
high-pressure and high-temperature sintering reveals that the N Kα band in the
both samples superimposes the inner X-ray Ti Ll line. This circumstance makes
difficulties in determination of the true shape of the band in the samples under
consideration. Results of our study reveal that the energy position of the maxi-
mum of the N Kα band does not change when going from the pristine mixture of
TiN and TiB2 powders to the TK-4 ceramics. Our results allow to conclude that
the peak intensity of the N Kα band with respect to that of the Ti Ll line is ca. 10%
higher in the mixture of TiN and TiB2 powders as compared to that in the TK-4
ceramics. For the two samples under study, the half-widths of the N Kα band are
similar (Table 2).
The X-ray emission B Kα bands of
the pristine mixture of TiN and TiB2
powders and the TK-4 ceramics under
consideration are presented in Fig. 4. For
the both samples under study, the energy
positions of the centers of gravity and of
the maxima «c» of the B Kα bands re-
main constant within the accuracy of
±0.2 eV, and the half-width of the band
does not change when going from the
powder TiN–TiB2 mixture to the TK-4
ceramics obtained by sintering the pow-
ders (Table 2). Nevertheless, as Fig. 4
shows, relative intensity of the low-
energy feature «b» of the B Kα band de-
creases from the value Ib/Ic = 0.33 ± 0.02
to Ib/Ic = 0.28 ± 0.02 and the fine-
structure feature «a» of the band becomes
more pronounced when going from the TiN and TiB2 powder mixture to the TK-4
ceramics obtained by high-pressure and high-temperature sintering the powders.
It should be mentioned that, on the first stage of sintering, mixtures of ultra-
fine TiN and TiB2 powders were undergone to high-pressure treatment at room
temperature. And only after the mentioned treatment, the samples were heated to
high temperature at high pressure as listed in Table 1. The so-called cold defor-
mation on the first stage of sintering leads to appearance in the samples under
Fig. 4. X-Ray emission B Kα bands of
the pristine mixture of ultra-fine TiN and
TiB2 powders (1) and of the TK-4 ce-
ramics obtained due to sintering the pow-
ders at 3.0 GPa and 1500oC for 3 min (2)
Физика и техника высоких давлений 2007, том 17, № 1
39
treatment of a number of defects, mainly
vacancies and dislocations, which can be
sewers for boron and nitrogen atoms in-
creasing their mobility. The creation of
vacancies in the non-metal sublattice of
titanium nitride can be considered as
«traps» for boron atoms as well as for
other atoms, e.g. oxygen and carbon,
which are present on the surfaces of
pristine TiN and TiB2 powders as the
present XPS results reveal (Fig. 5).
However, when studying the X-ray
emission Ti Kβ5 bands in the substances
under considerartion (Fig. 3), we did not
detect the presence of the so-called Ti
Kβ′′ subbands associated neither with
titanium oxide nor with titanium carbide.
Therefore, the presence of the above
non-metal impurities in the bulks of TiN and TiB2 powders and of the nanocrystal-
line TK-4 ceramics should be minor. In addition, as one can see from Fig. 4, the
well-pronounced feature «b» of the B Kα band vanishes almost completely when
going from the pristine TiN and TiB2 powder mixture to the TK-4 ceramics. As
shown in Ref. [22], the feature «b» of the B Kα band of TiB2 is created by the B 2p-
like states taking part in the formation of the B–B bonds in the compound. There-
fore, decreasing the relative intensity of the feature «b» of the B Kα band when
synthesizing the TK-4 ceramics from the ultra-fine TiN and TiB2 powder mixture
may be an indication of the formation of new B–N bonds in the TK-4 ceramics.
These phenomena can explain the rather high microhardness of the TiN-TiB2 ce-
ramics (17.48–29.65 GPa, Table 1). As it has been already mentioned, the existence
of B–B-bonds is characteristic of transition metal diborides. Substitution of some
boron atoms by nitrogen in TiB2 should lead to the formation of B–N bonds, which
are carriers of a number of very important properties, partly extremely high micro-
hardness (close to that of diamond) and plasticity. A decrease of the lattice parame-
ters a and c of TiB2 when sintering the TK-4 ceramics from the TiN and TiB2 pow-
der mixture at high pressure–high temperature conditions (3.0 GPa, 1500°C, 3 min)
may also indicate a possibility of the formation of B–N bonds in the ceramics stud-
ied. Indeed, lengths of the shortest B–B bonds in TiB2 are equal to 0.175 nm, while
those of B–N bonds in the lattice of sphalerite-like BN are about 0.157 nm. The de-
creasing half-widths of the Ti Lα and Ti Kβ5 bands when sintering the nanocrystal-
line TK-4 ceramics from the pristine TiN and TiB2 powder mixture also confirms a
statement about the creation of new bonds in the ceramic material.
It is necessary to mention that the present XPS studies indicate that the XPS N
1s and B 1s core-level binding energies do not change within accuracy of ±0.1 eV
Fig. 5. Survey of X-ray photoelectron
spectrum for the pristine mixture of ultra-
fine TiN and TiB2 powders (some addi-
tional signals originate from an aluminium
plate in which the powders were pressed)
Физика и техника высоких давлений 2007, том 17, № 1
40
when going from the pristine TiN and TiB2 powder mixture to the TK-4 ceramics.
This fact indicates that the charge state of the nitrogen and boron atoms do not
change significantly when synthesizing the TK-4 ceramics from the ultra-fine TiN
and TiB2 powder mixture. Studies of the XPS Ti 2p core-level binding energies
are in progress now. Such studies will allow us to set on a common energy scale
all the X-ray emission spectra obtained in the present paper for the pristine ultra-
fine TiN and TiB2 powder mixture and for the TK-4 ceramics and to discuss in
detail the question about the formation of new bonds in the ceramics.
4. Conclusions
It has been established that, when sintering the mixture of ultra-fine TiN and
TiB2 powders (80 wt.% TiN and 20 wt.% TiB2) at high-pressure and high-
temperature conditions (3.0 GPa, 1300–1500°C), interaction of these phases is
observed and nanocrystalline TiN–TiB2 ceramics with the microhardness of
17.48–29.65 GPa are synthesized. The crystal structure of the ceramics consists of
two phases, mainly of cubic TiN and hexagonal TiB2 components. When sintering
the TK-4 ceramics possessing the highest microhardness, mainly 29.65 ± 0.90 GPa,
the lattice parameters a and c of the TiB2 phase decrease but the lattice parameter
a of the TiN phase increases somewhat. The present X-ray emission spectroscopy
data indicate that the half-widths of the Ti Lα and Ti Kβ5 bands decrease by
(0.5–0.6) ± 0.2 eV when obtaining the nanocrystalline TK-4 ceramics from the
pristine mixture of TiN and TiB2 powders. The energy positions of the maxima
and of the centers of gravity of the N Kα and B Kα bands as well as their half-
widths remain constant within experimental errors for the both substances under
study. The present XPS core-level measurements reveal that the charge state of
the nitrogen and boron atoms do not change significantly when synthesizing the
TK-4 ceramics from the ultra-fine TiN and TiB2 powder mixture.
This work was partly supported by STCU through the projects № 1836 and
№ 3101.
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