Title of Invention

A PROCESS FOR THE MANUFACTURE OF MICROWAVE DIELECTRIC CERAMIC MATERIALS.

Abstract

Disclosed herein is a process for the manufacture of microwave dielectric ceramic materials with very high quality (Q) factors and negligible temperature coefficient of relative permitivity from the raw materials such as described herein which are taken in powder form, mixed thoroughly in stoichiometric proportions, pre calcined, wet-mixed and then subject to various stages of the sintering to get the desired products characterized in that pre calcined powders which are wet-mixed with required amounts of dopants and further substituents such as described herein.

Full Text

FIELD OF TECHNOLOGY This invention relates to the field of dielectric ceramics. Further this invention relates to a method of manufacture of microwave dielectric ceramics with very high quality (Q) factors and negligible temperature coefficient of relative permitivity. DESCRIPTION OF PRIOR ART Dielectric ceramic materials have been studied for decades due to their application in important technologies. Recent revolutions in microelectronics and, in particular, wireless communication technologies have elevated the importance of materials with the unusual combination of high dielectric constant, low dielectric loss and the least possible temperature coefficient of dielectric constant. The innovations in microwave wireless communications are the most dramatic changes in technology in the past decade. As in all technological systems, at the base of revolutionary changes in wireless communications are mainly due to the advances in materials. The materials used in the circuitry of microwave wireless devices have many features in common with materials for other microelectronics-based technologies. These unique innovations demand materials that have their own specialized requirements and functionalities. Applications of dielectric ceramics include microwave oscillators, narrowband microwave filters, radar detectors, cellular telephones, up or down linking microwave antenna substrates and global positioning satellite (GPS) devices. In many of these devices, the ceramic specimens used are designed to be dielectric resonators, functioning at the frequency of the carrier signal to allow that signal to be efficiently separated from other signals in the microwave band. The resonant frequency of the devices depends on the dielectric constant of the ceramics. The size of the resonator at any particular resonant frequency depends on the inverse of the square root of the dielectric constant of the material; thus, the larger the dielectric constant, the smaller size of the ceramic component needed. Unfortunately, there are other requirements for the resonators, which make almost all the materials with high dielectric constants, such as ferroelectrlcs. impossible to use for these applications. To be useful in microwave communication devices the dielectric constant of the material must not strongly depend on temperature. The practical requirement is that for a temperature range from -40 to 80° Q, the change in dielectric constant as a function of temperature should be as low as possible,_preferably less than 15 ppm / °C, Xhe dielectric loss of the material also should be very low with a quality factor, Q (defined as 1/dielectric loss tangent) better than 10,000. These requirements in combination eliminate the use of many conventional high dielectric constant materials such as ferroelectrlcs. The high dielectric constant at microwave frequencies, low temperature coefficient of dielectric constant and low dielectric loss are almost always mutually exclusive in dielectric materials. Further, the demands of mass production of the devices require reliable, reproducible processing of the ceramics, with tolerances of only a fraction of a ppm / °C in the temperature coefficient of dielectric constant and ±1% in dielectric constant from one component to the next. OBJECTS OF THE INVENTION The primary object of the invention is the manufacture of dielectric ceramic materials with a characteristic features of least changes in dielectric constant as a function of temperature change and with a high quality, factor (Q) to minimise the dielectric loss of the materials. It is another object of the invention is to select the raw materials for the manufacture of dielectric ceramic materials to achieve the desired characteristic features of the first object of the invention. It is another objective of this invention to invent a process of manufacture of the said dielectric ceramic material of the present invention. It is yet another objective of the invention to select and add dopants to the solid solutions of ilmenite-type and perovskite-type crystal structures for high miscibility of the two phases thereby lowering the temperature coefficient of dielectric constant (TCK) with almost no changes m the relative permittivity (Sr) and the dissipation factor (tan 5) of the ceramic materials of the present invention. In one of the embodiments by the process of the invention, the sintered density of the dielectric ceramic materials obtained should be greats than 98% of the single crystal values with zero porosity. This invention thus provides a process for the manufacture of microwave dielectric ceramic materials with very high quality (Q) factors and negligible temperature coefficient of relative permitivity from the raw materials such as described herein which are taken in powder form, mixed thoroughly in stoichiometric proportions, pre calcined, wet-mixed and then subject to various stages of the sintering to get the desired products characterized in that pre calcined powders which are wet-mixed with required amounts of dopants and Anther substituents such as described herein. Brief Description of the Accompanying Drawings: F1g.l X-ray diffraction patterns of (a) phase pure MgTiOj calcined at 1250oC for 4h(b) phase pure CaTiOs calcined at 1250'C for 3h and (c) solid solution,(Mg o.9Ca o.OTiOj calcined at 1200'C for 6h. Fig:2 The dielectric constant of the (Mgi.iCax)Ti03 as a fimction of the calcium contents at a frequency of 2 GHz. Fig3 The effect of frequency on the dielectric constant of the solid solution, (Mgi.x Cax)Ti03 for x= 0.05,0.1 and 0.15. Fig 4 Dissipation factor (tan 5 ) as a ftmction of measiuing fiuency for ceramics with 5,10 and 15 mol% calciirai. Fig.5 X-ray diffraction patterns of (MgcgCao.OTiOs cCTamics sintered at HOO'CC 1 h) with (a)no additive,(b)5 mol% AI2O3 ,(c)10 mol% AiiOs and (d) 20 moiro AlaOa. Fig. 6 X-ray diffraction patterns of (Mgo.gCaoOTiOs ceramics with 5 mol.% AI2O3 sintered at 1400°C for (a) 1 hour and (b) 3 hours. Fig. 7 The dielectric constant at a frequency of 2 GHz as a function of the amount of AI2O3 added for ceramics with 5, 10 and 15 mol.% calcium. Fig. 8 X-ray diffraction pattern of phase pure magnesium aluminium titanate (Mg4Al2Ti9025), calcined at 1250°C for 4 hours. Fig.9 XRD patterns of ceramic samples of (Mgo.5Cao.5)Ti03 sintered at 1400°C containing La203 and AI2O3 in different concentrations. Fig.10 Dielectric constant as a function of temperature at a frequency of 2 GHz for samples with 5-75 mol.% calcium and of Mg4Al2Ti9025. Fig.11 The change in temperature coefficient in electrical permittivity (TCK) with 'x' for the solid solution ,Mgi,xCaxTi03 ,for x = 0 to 1. Inset shows the effect of alumina addition. Fig.12Change in TCK with the addition of AI2O3 for (Mgi.x Cax)Ti03 solid solutions with 5. 10 and 15 mol.% calcium. Fig.13 Change in the temperature coefficient of permittivity (TCK) with addition of La203 + AI2O3 to (Mgi.xCa>i)Ti03 ceramics for different x-values. Fig.14 XRD patterns of ceramic samples of {Mgo,25Cao7)Ti03 sintered at 1425°C containing different La203 and AI2O3 concentrations. DETAILED DESCRIPTION OF INVENTION The detailed description of the process of manufacture of microwave dielectric ceramics with very high quality (Q) factors and negligible temperature coefficient of relative permittivity is described below and the description shall include the following: 1. Raw Materials Selection 2. Preparation of necessary chemicals 3. Ceramic Processing 4. Dielectric Characteristics 5. Effect of Dopants 6. Effect of Substituents in combination 7. Temperature coefficient of dielectric constant 8. Examples and 9. Figures (1 to 14) Raw Materials Selection Selection of raw materials with respect to chemical purity, particle size and reactivity are important in obtaining ceramics with phase-singularity and the desired densification characteristics. All the physical properties of the ceramics, particularly the dielectric losses are greatly affected by the raw materials. The titanates are prepared from titanium dioxide and carbonates of magnesium and calcium. Purity is an important factor to be considered. The carbonates are commonly contaminated with alkali halides especially sodium chloride. Alkali ions exhibit relaxational behaviour in titanate lattices and exhibit ionic conductivity of low magnitude, which in turn, increases the dielectric losses to unacceptable magnitudes, particularly at high frequencies. The selected powders have to be fine - grained so that the unreacted oxides should not be present in the final ceramics. Further, prevalence of mixed titanate phases is undesirable, with ilmenite-type (e.g. MgTiOs) as well as perovskite-type {e.g. CaTlOa) phases coexisting. In general, choice of appropriate raw materials is very critical in realizing high performance of the dielectric ceramics. Preparation of magnesium carbonate: Very high purity magnesium carbonate was prepared, wherein the high purity was attained by the method of fractional precipitation. The prepared compound is generally a mixed salt of magnesium carbonate and magnesium hydroxide in varying ratios, i.e. [MgCOaJi-x [Mg(0H)2]x (0 Magnesium chloride hexahydrate is used to prepare the carbonate. An approximately 1M solution of the magnesium chloride is prepared. 1.5M to 2M solution of ammonium carbonate is used for the precipitation. Fractional precipitation is initially done to remove the impurities present. In this method, ~ 5% of the magnesium is precipitated out first. The metal ion impurities present will also preferentially be precipitated along with the early formed magnesium carbonate. This is filtered off and the filtrate is heated to about 80°C and complete precipitation is carried out. The hydroxy carbonate of magnesium obtained is washed free of chloride. Since it has a solubility of - 0.3 g/litre, a saturated solution of magnesium hydroxy carbonate, or alternatively, aqueous ethanol is used for washing. It is then dried initially at 100°C and subsequently at 200°Cfor12-15hours. Because the carbonate/hydroxide ratio varies according to preparative conditions, estimation of the magnesium content Is done for every batch, which ranges from 50.2 to 54.6 wt %. Preparation of calcium carbonate: The same procedure employed for preparation of magnesium carbonate is followed. Calcium chloride dihydrate was used. Unlike the previous case, calcium forms readily the pure anhydrous carbonate. Preparation of magnesium titanate (MgliOO Magnesium titanate was prepared using magnesium carbonate and titanium dioxide. To prepare IGOOg of MgTiOs, 641g of magnesium hydroxy carbonate containing 52.3%MgO and 665g TIO2 were homogeneously mixed by a planetary mill using agate container with agate balls. Ethyl alcohol was used as the medium. Milling was done for 6 to 8 hours. The powder was then calcined initially at a temperature of 1100- 1150°Cfor4 to 5 hours, then milled again and subsequently calcined further at 1200 - 1250°C for 4 hours. The powder thus obtained was highly crystalline and phase-pure magnesium titanate with the ilmenite structure (Fig.1}. Preparation of magnesium calcium titanate (MgiCa,TiO,) Magnesium calcium titanate of varying Mg/Ca ratio is prepared the same way as magnesium titanate by the procedure described above. For example, to prepare 1000g of the composition with x = 0.1, 83.4g CaCOs, 570g magnesium hydroxy carbonate and 656g Ti02 are mixed homogeneously. It is then calcined at 1100 - 1200°C for 4 hours, milled again and calcined at a temperature between 1180 and 1250°C for 3 to 4 hours. The calcination temperature is varied based on the Mg/Ca ratio taken (Fig.1). Ceramic processing Processing includes various steps from the pre-calcined powders that result in polycrystalline ceramics with densities of > 98% of the corresponding single crystal values. Pre-treated powders are wet-mixed along with the required amounts of dopants, an organic binder, deflocculant and deionized water. 1 wt.% of polyvinyl alcohol is used as the organic binder added as an aqueous solution and 0.5 wt.% polyethylene glycol is used as the deflocculant. The mixture is dried at 60°C with continuous stirring. The granulated dry mixture is sieved through nylon meshes (60 to 200 mesh, IS). The granules are pressed in a die to the desired green strength having about 65% of theoretical density. The disks are sintered in a high temperature electrical furnace under the following schedule: 200°C/h 150°C/h 300-450°C/h R.T ► 600°C(1h) > The substrates used for sintering are platinum foils laid on to alumina plates. The organic matter present as binder and deflocculant is burnt out in a preliminary operation at about 600°C for 1 hour. The specimens are sintered at the selected temperature ranging from 1300 to 1450°C depending upon the amount of calcium present. The rate of heating is 120- 200°C/hour. The dwell time varied from 1 to 3 hours. The ceramics are then cooled at the rate of 300 - 450°C/ hour. Dielectric characteristics Tailoring the dielectric constant The relative permittivity, Sr, of polycrystalline magnesium titanate is 16.7 and that of calcium titanate is 180. Solid solutions of (Mgi-xCax)Ti03 have values of £, between these two values. It was found that the value of Sr increases linearly with 'x' as seen in Fig.2. This makes it possible to tailor the dielectric constant of the ceramic to any predetermined value using the linear regression relation. However, for calcium content above 3 mol.%, the TCK is strongly negative. Effect of frequency Some dielectric materials show higher dispersion, i.e. the dielectric constant and the dissipation factor increases as the frequency is lowered. This is highly undesirable because lower frequency dissipation can lead to material heat-up even when the applied a.c. field is of higher frequency through sub - overtones. The high frequency dispersion can be eliminated totally by improved processing conditions as well as material purity. The materials processing includes appropriate calcination at temperatures between 1150 and 1250°C, to yield sinterable, phase-pure powders. The sintering conditions and parameters are extremely important. The sintering temperature varied from 1300 to 1450°C with dwelling period between 1 to 3 hours, depending on the amount of calcium present. It is important that the ceramics achieve a density of > 98% of the theoretical density with zero porosity. Even a porosity of - 0.5% will significantly increase the dielectric losses. The presently prepared ceramics exhibited flat behaviour of Sr with respect to frequency (Fig.3) especially at lower frequencies where the space charge polarization dominates. The dissipation factor {tanS} was also very low, even at low frequencies as shown in Fig. 4. These ceramics have the Q value {1/tan8) of 30,000 to 50,000. Effect of dopants Magnesium titanate has ilmenite-type crystal structure and calcium titanate has perovskite structure. From X-ray diffraction studies, it was observed that the solid solutions of (Mg,Ca)Ti03 showed the presence of two phases: an ilmenite-type, magnesium-rich phase and a perovskite-type, calcium-rich phase. For the solid solutions considered here, the Mg-rich phase is the major one. However, the presence of even small amounts of the Ca-rich minor phase can significantly increase the TCK. Therefore, in order to bring the TCK to low levels, miscibility of the two phases is critical. It was found that the addition of aluminium oxide brought in very good miscibility of the two phases. Gamma phase of aluminium oxide was used in order to achieve high reactivity. On the addition of AI2O3, the TCK of these solid solutions were tremendously brought down to very low values, with almost no changes in the relative permittivity (Er) as well as the dissipation factor (tanS). For the compositions, [(Mgi.j \ of these process parameters are dependent on the amount of calcium present in the solid solutions. The XRD patterns in Fig. 5 correspond to those of the solid solution with 10 mol% calcium, sintered at 1400°C for 1 hour. Fig. 5(a) is the XRD pattern without additive. It shows the existence of the calcium-rich minor phase along with the magnesium-rich major phase. In Fig. 5 (b) it is seen clearly that the addition of 5% AI2O3 brings in miscibility of the two phases. This results in a reduction of TCK to - 3 ppm / °C from - 244 ppm / °C. However on further increase in alumina content, the MAT as well as the Ca-rich phase segregated out. This is seen clearly from Fig. 5 (c) and (d) corresponding to 10 and 20 mol.% AI2O3 respectively. Further, the amount of the MAT increases with alumina, as indicated by the increased intensity of the corresponding XRD peaks. Higher intensities of (121) and (002) peaks corresponding to the Ca-rich phase is explained on the basis that with more magnesium being taken away to form the MAT phase, there is increased segregation within the titanate solid solutions to Mg-rich ilmenite and Ca-rich perovskite. Fig, 6 shows the XRD patterns of the same solid solution sintered at 1400'C with increasing dwell time. Fig. 6 (a) has a dwell time of 1 hour, where complete miscibility is attained. Fig.6 (b) shows the diffraction pattern on increasing the dwell time to 3 hours. The MAT and the Ca-rich phases are clearly present. These phases have segregated out of the once miscible titanate solid solution. This is undesirable, as it will lead to increase in tan6 as well as TCK. The effect of increase in alumina content on the relative permittivity is shown in Fig. 7. it was seen that although the required amount of alumina is larger for higher Ca-containing compositions, there is only a marginal decrease of 0.5 to 1.5% in the value of relative permittivity. In order to study its dielectric properties, the MAT phase,Mg4Al2Ti9025, was synthesized separately. It was prepared by homogeneously mixing magnesium carbonate, y-AOa, and Ti02 in the required ratio and calcining at a temperature of 1250'C for 4 hours. Fig. 8 shows the X-ray diffraction pattern of the phase-pure powder so obtained. The powder was compacted and sintered at 1330°C for 2 hours. The ceramics obtained were found to have a relative permittivity of 16.7 and a TCK of - 4 ppm / °C. It has a Q value of 20,000 at a measuring frequency of 2 GHz, which can be further increased to 100,000 by post-sinter annealing. It showed very low dispersion particularly at lower frequencies. Effect of Substituents in Combination The results from the alumina addition indicated that the substitution of Ti* by AP"*" ions takes place in the titanate structures. Since the latter has one positive charge less (+3) than the ion which it replaces (+4), formation of the new phase such as MAT takes place. This can be avoided by having the simultaneous substitution of a higher valent cation at Mg- or Ca- sites. Thus, La, Nd, Sm, Gd or Y have been substituted together with equivalent amounts of Al* or Ga*. Thus, 0 to 20 mole% of AI2O3 or Ga203 was added together with the equivalent quantity of 13263, Nd203, Sm203, Gd203 or Y2O3 in Mg(i-x)CaxTi03 where x = 0,2 to 0.75. To this end. the raw materials were mixed and pre-calcined at 1150°C. Substitution of AP* or Ga* ions at Ti'** sites produces the anion (oxygen) vacancies for charge compensation so that the electro-neutrality is maintained. However, large concentrations of vacancies render the solids unstable so that second phase{s) such as MAT is formed. Substitution of La*, Sm*, etc at the Mg or Ca" sites produces cation vacancies, again for reasons of charge compensation. When equivalent concentrations of anion and cation vacancies are formed, they are mutually annihilated so that no second phase is generated. The phase-singular solids of the composition: (Mgi.(x-.y)Ca(x)Lay)(Tii.yAly)03 (x aluminium is replaced by gallium.With increase in x-value {Ca'Content)to >0.3,the crystal structure changes to rhombohedral or orthorhombic perovskite as the La and Al contents are increased i.e. y > 0.20. The relative permitivity of the ceramics, [Mgi.(j(+y)Ca(x)Lay]|Tii-y(AI/Ga)y]03 ranged from 25 to 50 with high Q-values of 30,000 to 60,000 when measured at 2GHz. The corresponding TCK varied from -A to +5 ppm/°C. Further, the dielectric constant is independent of frequency even at lower frequency ranges. The Q-values as well as TCK showed minimal changes on varying the sintering as well as the post-sinter annealing conditions. Temperature coefficient of dielectric constant /TCK) The temperature coefficient of dielectric constant is a very important factor to be considered for selecting the suitable dielectric material. For microwave applications, the value of TCK should be within 20 ppm / *C, for a temperature range of - 40°C to 100°C. Fig. 10 shows the effect of temperature on the dielectric constant for Mg4Ai2Ti9025 (MAT) as well as for the alumina added (Mg, Ca)Ti03 ceramics. These ceramics exhibit flat behaviour throughout the temperature range of utility in electronics devices. The TCK of the end-member magnesium titanate is +100 ppm / °C whereas that of calcium titanate is -1800 ppm / °C. Fig. 11 shows the TCK versus calcium content for the solid solution (Mgi-yCax)Ti03 for x = 0 to 1 without alumina addition; and the inset shows the effect of alumina addition at lower ranges of Ca-contents (x This clearly indicates that for a given amount of calcium, the corresponding amount of alumina required, as well as the temperature and duration of sintering have to be carefully optimized to bring in maximum miscibility and to retain this metastable state so as to realize ceramics with the lowest possible values of TCK. However such limitations of critical optimization of the processing conditions do not exist when alumina substitution is simultaneous to that of M2O3 (M = La, Nd, Sm, Gd or Y). Further, calcium contents can be raised to higher values i.e. x > 0.75. Fig. 13 shows that TCK diminishes with increasing y-value in (Mgi. (x+y)Ca(x)LaY){Tii.xAly)03 for a given calcium content. TCK reaches near zero values at the critical y-values, above which the TCK remain nearly invariant. At higher Ca-content, the critical value of y is shifted to the right hand side in Fig. 13. Example 1 (Mgo.95Cao,o5)Ti03 The powder was prepared from carbonates of magnesium and calcium, and Ti02 as described earlier. The first calcination was done at 1150°C and the second at 1230°C. The sintehng temperature was 1440°C for 1 hour. This solid solution gives a relative permittivity of 20. The Q value is 46,200. The TCK without any dopant is - 130 ppm / °C. This is brought down to 0 ppm / °C by the addition of 2 mol.% AI2O3 whereas the Q value is 55,000. Fig. 3 shows that the effect of frequency on the dielectric constant is negligible. Fig. 12 gives the TCK as a function of the amount of alumina added. At 2% AI2O3, the TCK is 0 ppm / °C, and further increase in AI2O3 mai Example 2 (Mgo.gCao.ijTiOs The first and second calcinations are carried out at 1150°C and 1200°C respectively. The temperature of sintehng is optimized at 1400°C for 1 hour. This gives a relative permittivity of 24.0. The Q value is 41,600. The TCK without any dopant is - 240 ppm / °C. This was brought to - 3 ppm / "C by the addition of 5mol,% AI2O3. As seen from Fig. 3 the dielectric constant is nearly independent of frequency. The addition of 5 mol.% AI2O3 lowers the relative permittivity only marginally {-1.3%) as shown in Fig. 7. Example 3 (Mgo.85Caoi5)TI03 The first calcination is done at 1150°C, followed by milling and subsequent calcination at 1200°C. The temperature of sintering is optimized at 1400°C for 1 hour. The solid solution has an Sr of 27.8, The Q value is 41,000. The TCK is brought down to -11 ppm / °C from -560 ppm/ °C with the addition of 9 mol.% AI2O3. Example 4 (Mgo.55Cao.3Lao.i5)(Tii].85Alo.i5)03 The powder is prepared from carbonates of magnesium and calcium, TiOa, gamma-alumina and La202C03. The first calcinations was at 1150°C and then remitted after cooling. The second calcination was at 1250°C. The sintering of the disc was at 1400°C for 3 hours. The solid solution was phase singular with the ilmenite-type structure. The relative permittivity is 37 at 25°C and the Q-value is around 58,000. The TCK is around +12 ppm/°C. All the measurements were performed at 2GHz frequency. Example 5 {Mgo,4Cao.35l-ao.25){Tio.75Alo.25)03 The powder was prepared by calcination as in Example 4. The sintering was carried out at 1450°C and the product was of rhombohedral perovskite-type structure with phase singularity. The relative permittivity is 43 (25°C) and the Q-value is 52.000. The TCK is around -8 ppm/°C; all values being measured at 2GHz. Example 6 (Mgo.7Cao.2Lao.i) (Tio.9Gao,i)03 The powder was prepared by calcination as in Example 4. The sintering was carried out at 1420°C. Phase-singular product of rhombohedral perovskite-type XRD pattern was obtained. All the measurements were done at 2GHz frequency. The relative permittivity is 29.2 at 25°C with a Q-value of 43.000. The TCK is -18 ppm/°C which is improved to +5 ppm/°C when reannealed at 1050°C for 8 hours. Example 7 (Mgo.i4Cao.4iLao.45) {Tlo.55Alo.45)03 The powder was prepared by calcination as in Example 4. The sintering was carried out at 1425°C. Phase-singular products with rhombohedral perovskite-type structure as per the XRD pattems were obtained (Fig.14). Dielectric measurements were carried out at 2GHz frequency. The relative permittivity is 47.5 at 25°C with a Q-value of 50,000. The TCK is -10 ppm/°C which is improved to +2 ppm/°C when reannealed at 1050°G for 8 hours. I Claim 1. The process for the manufacture of microwave dielectric ceramic materials with very high quality (Q) factors and negligible temperature coefficient of relative permitivity from the raw materials such as described herein which are taken in powder form, mixed thoroughly in stoichiometric proportions, pre calcined, wet-mixed and then subjected to sintering to get the desired products characterized in that pre calcined powders which are wet-mixed with required amounts of dopants and alongwith or without substituents such as described herein. 2. The process as claimed in claim 1, wherein the raw materials are MgCOs and CaCOs, oxides of titanium and aluminium taken in pure form. 3. The process as claimed in claim 2, the pure raw materials are obtained from their respective chlorides and made by removing the impurities present by the method of fractional precipitation 4. The process as claimed in claim 1, wheein the said ceramic materials are prepared by using phase-pure magnesium titanate and its solid solutions as (Mgi-iCax)Ti03 prepared by homogeneously mixing magnesium carbonate, calcium carbonate and titanium dioxide by ball milling and calcining at a temperature betweenl 150" to 1250 to yield a phase pure reactive powder. 5. The process as claimed in claim 1, wherein the ceramic materials obtained as dielectric constant randing from 16 to 50 when measured in the microwave frequencies. 6. The process as claimed in preceding claims, wherein the dielectric constant of the said ceramic materials is capable of being tailored to any required value between 16 and 50 by suitably varying 'x' value from 0 to 0.45 in the solid solution (Mgi-xCajJ Ti03 form the raw materials. 7. The process as claimed in claim 1, wherein the dopant is gamma AI2O3. 8. The process as claimed in claim 7, wherein the gamma aluminium oxide is added in the range of 5 to 20 mol.%. 9. The process as claimed in claim 1, wherein the substituents are added in desired amounts from which the formation of new phase such as Magnesium Alumino Titanate (MAT) is avoided. 10. The process as claimed in claim I, wherein the substituents are selected from La, Nd, Sm, Gd, Ga, Y tjv- DTt-ide* thereof. 11. The process as claimed in claims 9 and 10, wherein the amount of substituents varies from 0 to 30 mol.%. 12. The process as claimed in claims 9 and 10, wherein the miscibility between magnesium titanate and calcium titanate is extended to x <_0.8 when substituted additives in combination are used e.g. ai2o3 gaoa etc. up to mol. the resulting phase has ilmenite-type changing over rhombohedral or orthorhombic peiovskite structure and sinterable high density ceramics.> 13. The process as claimed in claims 12, wherein the said ceramics obtained have dielectric constants of 30-50 in the microwave frequencies with Q-values upto 50,000 and TCK of 14. The process as claimed in any one of preceding claims, where the dielectric constant of the said ceramics increases in a near linear fashion from 16 to 50 with 'x-values ranging from 0 to 0.45'. 15. The process as claimed in any one of preceding claims, wherein the said dielectric ceramics have very high Q(l/tan5) of 30,000 to 60,000 at a frequency of 2 GHz. 16. The process as claimed in any one of preceding claims, wherein the dielectric constants of the said ceramics are constant within a frequency range of 100OHz and 2 GHz. 17. The process as claimed in any one of preceding claims, wherein the said ceramics have the temperature coefficient of dielectric constant (TCK) is 18. The process as claimed in any one of preceding claims, wherein the y-AI2O3 so added along with magnesium and titianium forms Mg4Al2Ti9025 (MAT), the ceramics from mat have dielectric constant around 16.5 and TCK of-4 ppm/C at 2 Ghz an the Q-values are as high as 100,000 after. , annealing the sintered disks in static air at 1100°C for 12 hours and cooled to room temperature at 30°C/hour. 19. The process as claimed in claim 1, wherein the dielectric constant of the said ceramics can be tailored to any required value between 16 and 50 by • varying 'x values 0 to 0.45' in the solid solution (Mg1-xC) Ti03. 20. The process for the manufacture of microware dielectric ceramic with very high quality (Q) factors and negligible temperature coefficient of relative permitivity substantially described herein exemplified and illustrated with the accompanying drawmgs.

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