We recorded infrared, Raman, and surface-enhanced Raman scattering (SERS) spectra of metal−string complexes Ni5(tpda)4X2 and Co5(tpda)4X2 (tpda = tripyridyldiamido, X = Cl−, NCS−) and free ligand ...tripyridyldiamine (H2tpda) to determine their vibrational wavenumbers and the strength of the metal−metal bonds. For SERS measurements, these complexes were adsorbed on silver or gold nanoparticles in aqueous solution to eliminate the constraint of a crystal lattice and to maintain the complexes in thermal equilibrium. The spectra of SERS and Raman modes show insignificant deviation in spectral features and band positions. We observe a single breathing band of pyridyl in Co5(tpda)4X2, indicating the existence of only the symmetric form, whereas split pyridyl lines are observed for Ni5(tpda)4X2 and assigned to arise because of a varied environment of coordination: square planar for the inner nickels and square pyramidal for the outer nickels in the complexes. From our analysis of the vibrational normal modes, we assign lines at 257/266 and 302/313 cm−1 to Ni5, at 287/284 and 355/360 cm−1 to Co5 symmetric stretching modes, and at 255/267 and 297/305 cm−1 and 319/323 and 391/392 cm−1 to Ni5 and Co5 asymmetric stretching, respectively, for complex with axial ligand Cl/NCS. The bonding in Ni−Ni is weaker than for Co−Co, consistent with the prediction from molecular-orbital theory.
The microwave dielectric properties and the microstructures of the (1
−
x)Mg
4Nb
2O
9–
xSrTiO
3 ceramic system prepared by the conventional solid-state route were investigated. SrTiO
3 was employed ...as a
τ
f
compensator and was added to Mg
4Nb
2O
9 to achieve a temperature-stable material. Corundum-structured Mg
4Nb
2O
9 and perovskite-structured SrTiO
3 were coexisted and the two-phase system was confirmed by the XRD and EDX analysis. Dielectric properties are correlated to the sintering temperature and the compositional ratio of the specimens. Although the
ɛ
r
of the specimen could be boosted by increasing amount of SrTiO
3, it would instead render a decrease in the
Q
×
f. The
τ
f
value is strongly correlated to the compositions and can be controlled through the existing phases. In fact,
τ
f
could be adjusted to near-zero by mixing 60
mole% Mg
4Nb
2O
9 and 40
mole% SrTiO
3. A dielectric constant (
ɛ
r
) of 21.02, a high
Q
×
f value of 112,000
GHz (measured at 9.7
GHz) and a temperature coefficient of resonant frequency (
τ
f
) of 1.6
ppm/°C were obtained for 0.6Mg
4Nb
2O
9–0.4SrTiO
3 sintered at 1300
°C for 4
h. It is proposed as a very promising dielectric material for low-loss microwave and millimeter wave applications.
The microwave dielectric properties and the microstructures of the (1
−
x)(Mg
0.95Co
0.05)TiO
3–
x(Na
0.5Nd
0.5)TiO
3 (0.1
≤
x
≤
0.18) ceramic system have been investigated. The two phase system was ...confirmed by XRD and EDX analysis throughout the entire experimental range. In this system, the microwave dielectric properties can be effectively controlled by varying the
x value. The dielectric constant ranged from 18.3 to 25.4 as the
x varies from 0.1 to 0.18. With the increase of sintering temperature, the
Q
×
f increased to a maximum and decreased thereafter. A maximum
Q
×
f
∼
112,000
GHz (where
f
=
8.6
GHz, is the resonant frequency) was achieved for samples with
x
=
0.1. For practical applications, a new microwave dielectric material, 0.84(Mg
0.95Co
0.05)TiO
3–0.16(Na
0.5Nd
0.5)TiO
3, is suggested and possesses a good combination of dielectric properties:
ɛ
r
∼
24.39,
Q
×
f
∼
70,000
GHz,
τ
f
∼
1.6
ppm/°C. It is proposed as a suitable candidate dielectric for GPS patch antennas and passive components in wireless communication system.
Solid solutions of (Mg
1−
x
Ni
x
)Al
2
O
4
(
x
=0–1) have been prepared using the solid‐state reaction method and their dielectric properties were measured at microwave frequencies. Formation of ...single‐phase spinel‐structured solid solutions was confirmed by X‐ray diffraction analysis throughout the entire compositional range, and the measured lattice parameters varied linearly from 8.0810 Å at
x
=0 (MgAl
2
O
4
) to 8.0445 Å at
x
=1 (NiAl
2
O
4
) leading to a linear decrease in the unit cell volume from 527.71 to 520.59 Å
3
. The ionic polarizability obtained, however, increased with the increase of
x
to a maximum at
x
=0.25 and decreased thereafter. It shows only a small variance in the ɛ
r
with Ni substitution for Mg and a maximum ɛ
r
of 8.21 was achieved for (Mg
0.75
Ni
0.25
)Al
2
O
4
in response to the highest ionic polarizability and relative density. However, the
Q
×
f
value can be significantly promoted up to a maximum value of 130 000 GHz (measured at 15.4 GHz) at
x
=0.25. In addition, substitution of Mg by Ni also helps to decline the τ
f
value from −65 ppm/°C at
x
=0 to −53.5 ppm/°C at
x
=0.25.
Solid solutions of (Mg...Ni...)Al...O... (x=0-1) have been prepared using the solid-state reaction method and their dielectric properties were measured at microwave frequencies. Formation of ...single-phase spinel-structured solid solutions was confirmed by X-ray diffraction analysis throughout the entire compositional range, and the measured lattice parameters varied linearly from 8.0810 ... at x=0 (MgAl...O...) to 8.0445 ... at x=1 (NiAl...O...) leading to a linear decrease in the unit cell volume from 527.71 to 520.59 ... The ionic polarizability obtained, however, increased with the increase of x to a maximum at x=0.25 and decreased thereafter. It shows only a small variance in the ... with Ni substitution for Mg and a maximum ... of 8.21 was achieved for (Mg...Ni...)Al...O... in response to the highest ionic polarizability and relative density. However, the Q...f value can be significantly promoted up to a maximum value of 130 000 GHz (measured at 15.4 GHz) at x=0.25. In addition, substitution of Mg by Ni also helps to decline the ... value from -65 ppm/...C at x=0 to ...53.5 ppm/...C at x=0.25. (ProQuest: ... denotes formulae/symbols omitted.)
The microwave dielectric properties and microstructure of the two-phase (Mg
0.95Zn
0.05)TiO
3–CaTiO
3 ceramic system were investigated. Dielectric properties of (Mg
0.95Zn
0.05)TiO
3 ceramics could ...be effectively promoted by adding CaTiO
3 to the specimen. At 1300 °C, 0.95(Mg
0.95Zn
0.05)TiO
3–0.05CaTiO
3 ceramic possesses good combination of microwave dielectric properties; a dielectric constant
ε
r of ∼
20.4, a
Q
×
f value of ∼
109,300 GHz (at 10 GHz), and a
τ
f value of ∼
−
12.42 ppm/°C. The τ
f value is strongly correlated to the compositions and can be controlled through the compositional ratio. With
x
=
0.07, a dielectric constant
ε
r of ∼
22.6, a
Q
×
f value of ∼
93,200 GHz (at 10 GHz), and a
τ
f value of ∼
−
2.62 ppm/°C was obtained for 0.93(Mg
0.95Zn
0.05)TiO
3–0.07CaTiO
3 ceramic sintered at 1300 °C for 4 h.
The microwave dielectric properties and microstructures of the new (1
−
x)MgTiO
3–
xCa
0.6La
0.8/3TiO
3 ceramic system, prepared using a mixed oxide route, were investigated. Combination of MgTiO
3 ...(MT) and Ca
0.6La
0.8/3TiO
3 (CLT) forms a two-phase system and leads to a near-zero
τ
f
. With increasing
x, the microwave
Q
×
f decreased and
ε
r
increased. A microwave dielectric material having a
ε
r
of 25.45, a
Q
×
f of ~
82,500 GHz (at 8.5 GHz), and a
τ
f
of ~
0.5 ppm/°C can be obtained from the compound 0.85MgTiO
3–0.15Ca
0.6La
0.8/3TiO
3 sintered at 1275 °C for 4 h. It is proposed as a candidate material for ISM band components and GPS antennas.
The dielectric properties and microstructures of 0.92(Mg sub(0.95)Co sub(0.05)) sub(2)TiO sub(4)-0.08(Ca sub(0.8)Sr sub(0.2))TiO sub(3) ceramics with B sub(2)O sub(3) additions have been ...investigated. The sintered 0.92(Mg sub(0.95)Co sub(0.05)) sub(2)TiO sub(4)-0.08(Ca sub(0.8)Sr sub(0.2))TiO sub(3) ceramics were characterized by using X-ray diffraction spectra, scanning electron microscopy (SEM), backscattering electron image (BEI) and energy dispersive X-ray (EDX). The dielectric properties are strongly dependent on the densifications and the microstructures of the specimens. The decrease of Q x f value at high-level B sub(2)O sub(3) addition was owing to the inhomogeneous grain growth and the high-dielectric-loss of the liquid phase. In comparison with that of pure 0.92(Mg sub(0.95)Co sub(0.05)) sub(2)TiO sub(4)-0.08(Ca sub(0.8)Sr sub(0.2))TiO sub(3) ceramics, specimen with 0.5 wt% B sub(2)O sub(3) addition possesses a substantial fine combination of dielectric properties (an inline image sub()rof 18.07, a Q x f of 95,000 GHz at 9.5 GHz and a t sub()fof -4.7 ppm/C) at a lower sintering temperature of 1200 C for 4 h. Moreover, a band-pass filter is also designed and simulated on the proposed dielectric to study its performance.
A theoretical analysis and design technique that can be employed in the fabrication of inhomogeneous coupled-stripline resonator bandpass filters is presented. The technique is also suitable for bulk ...dielectric ceramic bandpass filters that are modified from quasi-coupled striplines.
Low‐loss ceramics in the system (Mg 1− x Ni x ) 2 TiO 4 ( x =0.02–0.1) have been prepared using the conventional solid‐state ceramic route. The formation of (Mg 1− x Ni x ) 2 TiO 4 ( x =0.02–0.1) ...solid solutions was confirmed by the EDX analysis and the lattice parameters measured, which linearly varied from Mg 2 TiO 4 ( a = b = c =8.4410 Å) to (Mg 0.9 Ni 0.1 ) 2 TiO 4 ( a = b = c =8.4335 Å). The X‐ray diffraction analysis also confirmed the coexistence of a cubic‐structured (Mg 1− x Ni x ) 2 TiO 4 and an ilmenite‐structured second phase (Mg 1− x Ni x )TiO 3 . By increasing x , not only could the Q × f of the (Mg 1− x Ni x ) 2 TiO 4 solid solution be considerably increased from 150,000 GHz at x =0 to a maximum 238,000 GHz at x =0.05, the highest ɛ r ∼16.43 could also be obtained simultaneously. This was mainly due to the uniform grain morphology and the highest density of the specimen. A good combination of microwave dielectric properties (ɛ r ∼16.43, Q × f ∼238,000 GHz at 9.8 GHz, and τ f ∼−55 ppm/°C) can be achieved for a specimen using (Mg 0.95 Ni 0.05 ) 2 TiO 4 sintered at 1400°C for 4 h.
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