1. G. brown, M.A.A. Issa and K.N.R. Taylor
“Anomalous nuclear resonance behaviour of 59Co in GdCo2”
J. Phys. F: Metal Phys., 1, L10-L12 (1971).
2. E. Dormann, K.H.J. Buschow, K.N.R. taylor,
G. Brown and M.A.A. Issa
“A study of the lineshape of the NMR spin echo spectra of the
compounds Cd1-x Yx Al2 and Gd1-x Lax Al2”
J. Phys. F: 3, 220-232 (1973).
3. P. Miles, M.A.A. Issa, K.N.R. taylor and G.J. Bowden
“Spin adjustment in (Ga, Dy) Al2”
J. Phys. F: Metal Phys. Vol.7, No.11, 242-2429 (1977).
4. S. Hedewy, M.A.A. Issa and M. Isskander
“E.S.R. Study of Some Copper (11) – Aray1 hydrazone –
Spectroscopy letters, 11(11) – 901-912 (1978).
5. S. Hedewy and M.A.A. Issa
“E.S.R. Study of Coper (11) – Doped Triglycine Selenate T.G. Se”
Spectroscopy letter, 1(12), 987-995 (1978).
6. N.M. Molokhia and M.A.A. Issa
“dielectric properties of BaTiO3 modified with ZrO2”
Pramana Vol.11, No.3, 289-293 (1978).
7. A.S. El-Hiti and M.A.A. Issa
“Structural anisotropy factor for basal reflections of Bentonite”
Central Glass and Ceramic Bulletin, Vol.25, No.1, 25-27 (1978).
8. N.M. Molokhia and M.A.A. Issa
“The Dielectric Behaviour of Graphite Doped BaTiO3”
J. Fac. Sci. Riyadh Univ., vol.9, 207-216 (1978).
9. M.A.A. Issa, A.S. El-Hiti and M.H. Wahabah
“The Chemical and the X-Ray Analysis of Some Saudi Arabia Minerals”
T.I.Z. Fachberichte, Vol.104, No.11, 751 (1980).
10. A.S. El-Hiti, M.A. Issa and M.H. Elboragy
“X-Ray Identification of Saudi Arabian Clay”
Sprechsaal, Vol. 113, No.4 275 (1980).
11. A.H. Bassyouni, M.A.A. Issa and A.F. Hafez
“Effect of A Magneitc Field On Lorentz Collisions In Acetylene – Air Flames”
J. Quant. Spectrosocpy Radiat. Trasfer. Vo.23, 503-512 (1980).
12. L.B. Chiu, P.R. Elliston, A.M. Stewart, K.N.R. Taylor and M.A.A. Issa
“Electron Spin Resonance of Gd(Cox Al1-x)
J. Phys. F: Metal Phys., 10, 2297-2303 (1980).
13. E.M. Sayed, M.A.A. Issa and M.A. Abdelmomen
“Investigation of the magnetic properties of I 116”
Atomkernenergie Vol. 37, No.1(63-64) (1981).
14. A.S. El-Hiti, N. Molekhia and M.A.A. Issa
“Electrical and x-Ray Diffraction Studies of Some New Organic Compounds)
Dirasat: J. Coll. Educ., King Saud Univ., Vol.4, 53-66 (1982).
15. M.A.A. Issa, N.M. Molokhia and Z.H. Dughaish
“Effect of cerium oxide (Ce O2) additives on the di-electric properties of BaTiO3 ceramics.
J. Phys. D: Appl. Phys., 16, (1109-1114) (1983).
16. M.A.A. Issa, N.M. Molokhia and S.A. Nasser
“Factors affecting the permittivity of Gd-doped BaTiO3”
J. Phys. D: Appl. Phys., 17, 571-578 (1984).
17. M.A.A. Issa, A.M. Hassib and Z.H. Dughaish
“A study of the BaTiO3: CeO2 Crystal structure by EPR”
J. Phys. D: Appl. Phys. 17, 2037-2046 (1984).
18. N.M. Molokhia, M.A.A. Issa and S.A. Nasser
“Dielectric and X-Ray Diffraction Studies of Barium titanate Doped with Ytterbium”
J. Am. Ceram. Soc. Vol. 67, No.4 (289-291) (1984).
19. A.M. Hassib, A.A.S. Musmus and M.A.A. Issa
“Conduction Electron Spin Resonance”
Phys. Stat. Sol.(a) 89, (147-153) (1985).
20. F.A.A. Amin, M.A.A. Issa, A.M. Hassib and Z.H. Dughaish
“Hot pressing of isothermally solidified Ge-Si thermoelectric alloys”
J. Mater. Sci. 20(1985) 4130-4138.
21. M.A.A. Issa, F.A.A. Amin, A.M. Hassib and Z.H. Dughaish
“Preparation of heavily doped n-type Ge-Si thermoelectric alloys”
J. Mater. Sci. 20(1989) (2300-2304).
22. F.A.A. Amin, A.S.S. Al-Ghaffari, M.A.A. Issa and A.M.Hassib
“Thermoelectric properties of fine grain (75% Sb2Te3 – 25% Bi2 Te3)
P-type and (90% Bi2 Te3 – 5% Sb2 Te3) n-type alloys”
J. Mater. Sci. 27(1992) (1250-1254).
23. M.A.A. Issa
“Electrical Properties of Polycrystalline PTCR Barium Titanate”
J. Mater. Sci. 27(1992) (3685-3692).
24. M.A.A.Issa, A.M. Hassib and F.A.A. Al-Hasson
“A Study of the Temperature Dependence of the Resistivity and Permittivity of n-type Semiconducting Barium Titanate: PrO2 Ceramics”
J. King Saud University, Sci., 1, 6 (1994) (3-29).
The abstracts of the above Publications are:
A study of the BaTiO3:CeO2 crystal structure by EPR
M A A Issa, A M Hassib and Z H Dughaish
J. Phys. D: Appl. Phys. 17 No 10 (14 October 1984) 2037-2046
Dept. of Phys., King Saud Univ., Riyadh, Saudi Arabia
Abstract. The crystal structure of BaTiO3:CeO2 was studied using the ESR spectrum of Fe3+ ions, contaminating pure BaTiO3, in the temperature range -160 degrees C to +160 degrees C. The observed powder spectra are classified into three parts: pure, lightly doped (0.05-0.5 mole% CeO2), and heavily doped (1-3 mole% CeO2)BaTiO3. The EPR spectrum of pure BaTiO3 showed five resonance lines, at room temperature, around g=2. On lowering the temperature, the five lines tend to converge towards the central line. The lightly doped EPR spectra reflected that the crystal fields experienced by Fe3+ ions are highly inhomogeneous and g-values in all the range g=12 to g=1.8 may be observed. The heavily doped samples reflected an obvious stabilisation of crystal structure with variation of temperature. The g-value reflected the effect of the dopant concentration and showed little or no variation with temperature. All observations confirm the possibility of observing crystallographic phase changes in ferroelectric polycrystalline BaTiO3 with different CeO2 concentrations by observing the EPR spectra of high spin (Fe3+) ions in polycrystalline BaTiO3 at various mperatures.
Factors affecting the permittivity of Gd-doped BaTiO3
J. Phys. D: Appl. Phys. 17 No 3 (14 March 1984) 571-578
M A A Issa, N M Molokhia and S A Nasser
Phys. Dept., King Saud Univ., Riyadh, Saudi Arabia
Abstract. The permittivity of BaTiO3 doped with small concentrations of Gd2O3 (0.01 approximately 0.1 mol.%) are found to be remarkably dependent on the type of the solid solution formed between Gd2O3 and BaTiO3. The decrease of permittivity at the Curie peak with decreasing grain size for BaTiO3 doped with concentrations of Gd2O3 from 0.5 approximately 3 mol.% is attributed to the formation of defective non-ferroelectric grain boundary layers of low permittivity.
Effect of cerium oxide (CeO2) additives on the dielectric properties of BaTiO3 ceramics
M A A IssaN M MolokhiaZ H Dughaish
J. Phys. D: Appl. Phys. 16 No 6 (14 June 1983) 1109-1114
Dept. of Phys., King Saud Univ., Riyadh, Saudi Arabia
Abstract. The effect of adding 0.05 to 16.2 mol.% CeO2 on the dielectric properties and loss tangent of sintered BaTiO3 was investigated at different temperatures. The permittivity increased with CeO2 additions up to 0.5 mol%, then decreased with increasing concentrations. In the samples doped with 5.6 and 16.2 mol.% CeO2 the curves show a slight increase in the permittivity with temperature, without any significant tendency to a peak value, down to room temperature. Smaller additions of CeO2 (0.05 to 2 mol.%) lower the Curie temperature to 92 degrees C. The loss tangent maximum (tan delta )max at the Curie temperature was less than 0.035 for pure BaTiO3 and 0.0120 for samples containing 16.2 mol.% CeO2. X-ray measurement shows that the lattice parameters change with the concentration of additive, the a axis expanded while the c axis shrank, approaching a cubic structure at room temperature for 5.6 mol.% CeO2(c/a=1.001249). Shrinking of the c axis reached its maximum at 16.2 mol.% CeO2 (c/a=0.994341).
Electron spin resonance of Gd(CoxAl1-x)2
L B ChiuP R EllistonA M StewartK N R TaylorM A A Issa
J. Phys. F: Met. Phys. 10 No 10 (October 1980) 2297-2303
School of Phys., Univ. of New South Wales, Sydney, NSW, Australia
Abstract. Electron spin resonance measurements for the pseudobinary system Gd(CoxAl1-x)2 with x<or=0.6 are reported. The results indicate a change of sign of the Gd-conduction-electron interaction parameter J at x approximately=0.3. This is shown to be consistent with a variation of the Curie temperature with x.
Spin adjustment in (Gd,Dy)Al2
P MilesK N R TaylorG J BowdenM A A Issa
J. Phys. F: Met. Phys. 7 No 11 (November 1977) 2421-2429
School of Phys., Univ. of New South Wales, Kensington, NSW, Australia
Abstract. Spin echo measurements have been used to establish the way in which the magnetic moments in GdAl2 adjust themselves to the presence of dysprosium ions introduced substitutionally into the lattice. The dysprosium moments favour a (100) easy magnetisation direction in contrast to the (100) of the GdAl2 lattice. The results suggest that the gadolinium moment directions change gradually from the (111) direction and a model is examined for spherical volumes of gadolinium ions about each dysprosium.
A study of the lineshape of the NMR spin echo spectra of the compounds Gd1-xYxAl2 and Gd1-xLaxAl2
E DormannK H J BuschowK N R TaylorG BrownM A A Issa
J. Phys. F: Met. Phys. 3 No 1 (January 1973) 220-232
Abstract. NMR spin echo spectra of Gd1-xYxAl2 and Gd1-xLaxAl2 (0<or=x<or=0.30) were studied in the ferromagnetically ordered state at 4.2 K. The Al resonance line profiles were analysed under the assumption of various models for the spatial extent of the conduction electron polarization and general confirmation of a RKKY like oscillatory polarization was found. Slowly decreasing nonoscillatory polarization functions are shown to be unable to explain the observed spectra. The line shape is shown to depend rather critically on the value of the Fermi wavevector kF. The polarization seems to decrease less strongly with distance than might be expected from the RKKY function.
Anomalous nuclear resonance behaviour of 59Co in GdCo2
G BrownM A A IssaK N R Taylor
J. Phys. F: Met. Phys. 1 No 2 (March 1971) L10-L12
Department of Physics, University of Durham, South Road, Durham.
Abstract. Spin echo measurements of the 59Co nuclear resonance in GdCo2 have revealed a rapid decay of the spin-echo amplitude with temperature up to 40 K followed by a further growth up to 79 K and subsequent decay above this temperature.
E. P. R Study Of Copper (II) - Doped Triglycine Selenate (TGSe)
S. Hedewy a; M. A. A. Issa a
Spectroscopy letters, 11(12), 987-995 (1978)
a Faculty of Sciences, University of Riyad, Saudi Arabia
The angular dependence of EPR of the Cu2+ ion in the ferroelectric TGSe crystal has been investigated. The coordination of the Cu2+ ion and the number of complexes were found to be the same as in the isomorphous copper doped TGS crystal. The spin density on the central metal ion indicates a more covalent nature of the Cu-ligand bond in TGSe. The spectroscopic splitting factor exhibits an anomaly near the ferroelectric transition point.
M. A. A. Issa1
J. Mater. Sci. 27(1992) (3685 – 3692)
Materials Study Group, Department of Physics, Faculty of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia
Abstract Semiconducting n-type barium titanate with a positive temperature coefficient of resistance (PTCR) has been made by doping BaTiO3 with 0.4 mol% Ho2O3. The d.c. resistivity, a.c. resistivity (1.2 kHz) and relative permittivity (1.2 kHz) at different temperatures between room temperature and 523 K have been measured. The high relative permittivity and the PTCR effect are attributed to the existence of potential barriers at the grain boundaries as proposed by Heywang. The height of the potential barrier has been calculated as a function of temperature on the basis of the Heywang model, using the measured resistivity versus temperature and relative permittivity versus temperature above the Curie temperature. Several different kinds of electrode have been used to study the effect of the contact on measurements of resistivity and relative permittivity.
Thermoelectric properties of fine grained (75% Sb2Te3-25% Bi2Te3)p-type and (90% Bi2Te3-5% Sb2Te3-5% Sb2Se3)n-type alloys
F. A. A. Amin1, A. S. S. Al-Ghaffari1, M. A. A. Issa1 and A. M. Hassib1
J. Mater. Sci. 27(1992) (1250 – 1254)
Materials Group, Department of Physics, Faculty of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia
Abstract The thermoelectric properties of fine-grained alloys prepared by either cold pressing and sintering or hot pressing in the range 5–50 µm are compared with single-crystal best-direction values. It is shown that for thep-type alloy, almost the entire thermoelectric properties are recovered, i.e. the figure of merit for the finest grain size is almost the same as the best single-crystal value. The same trend is observed in then-type alloy except that 90% of the single-crystal figure of merit is recovered. These results are discussed in terms of a model which suggests that degradation of favourable thermoelectric properties by powdering the alloys is compensated by (1) decrease of thermal conductivity due to scattering of phonons at grain boundaries for grain sizes that are comparable to the mean free path of phonons; and (2) retention of some of the anisotropic properties of the single crystal in the fine-grained compacts.
Hot pressing of isothermally solidified Ge-Si alloys
F. A. A. Amin1, M. A. A. Issa1, A. M. Hassib1 and Z. H. Dughaish1
J. mater. sci. 20(1985) 4130 - 4138)
Materials Study Group, Department of Physics, Faculty of Science, King Saud University, PO Box 2455, Riyadh, Saudi Arabia
Abstract Germanium-silicon alloys of nominal composition Ge50-Si50 atomic fraction have been prepared by isothermal solidification and hot-pressing at temperatures up to 1350 K and pressure of 178 MPa. It is shown that high degree of homogenization can be obtained in the final compact. This work lends further evidence for the plastic flow mechanism of the sintering of these alloys.
Preparation of heavily doped n-type Ge-Si thermoelectric alloys
M. A. A. Issa1, F. A. A. Amin1, A. M. Hasstb1 and Z. H. Dughaish1
J. mater. sci. 20(1989) (2300 - 2304)
Materials Study Group, Department of Physics, Faculty of Science, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia
Abstract Germanium-silicon alloys doped with phosphorus were prepared in vacuum by rapidly pouring the molten alloy into cooled copper moulds containing the phosphorus dopant. Without any further treatment, the ingots are milled into powder of grain size (L≤5 µm) and hot pressed. It is shown that a high degree of homogenization of the alloy constituents can be obtained in the final compacts, thus eliminating the need for zone-levelled starting material. It is also shown that this work is in agreement with the plastic flow model of sintering known as the Mackenzie-Shuttleworth-McClelland model. Electrical measurements indicate that the dopant is effectively and uniformly incorporated into the alloy.
Dielectric and X-Ray Diffraction Studies of Barium Titanate Doped with Ytterbium
N. M. MOLOKHIA1, M. A. A. ISSA1 and S. A. NASSER1
J. am. ceram. Soc.67(4) 289 - 291 (1984)
Physics Department, King Saud University, Riyadh, Saudi Arabia