BaO-xTiO2 dielectric ceramic composition

Abstract: Disclosed is a BaO-xTiO₂ dielectric ceramic composition (x = 3.5 to 4.5) containing BaTi₄O₉ and Ba₂Ti₉O₂₀, wherein the content ratio of Ba₂Ti₉O₂₀ {Ba₂Ti₉O₂₀/(BaTi₄O₉ + Ba₂Ti₉O₂₀) } obtained by a X-ray diffraction maximum peak height integration method described below is less than 0.19. content ratio of Ba₂Ti₉O₂₀ = {a peak height ascribed to the (421) face of Ba₂Ti₉O₂₀ + a peak height ascribed to the (222) face thereof) /[ { a peak height ascribed to the (200, 140) face of BaTi₄O₉ + a peak height ascribed to the (121) face thereof + a peak height ascribed to the (230, 150) face thereof } + {a peak height ascribed to the (421) face of Ba₂Ti₉O₂₀ + a peak height ascribed to the (222) face thereof} ]. In the above dielectric ceramic composition, it is possible to prevent the occurrence of hexagonal pattern cracks and hence to improve the yield.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a BaO-xTiO 2 dielectric ceramic composition, aid more particularly, to a BaO-xTiO 2 dielectric ceramic composition having Ba 2 Ti 9 O 20 /(BaTi 4 O 9 + Ba 2 Ti 9 O 20 ) ratio of less than 0.19 for preventing the occurrence of hexagonal pattern cracks. The present invention is applicable for the impedance matching or the like in a dielectric resonator (particularly, one with a large size of 50mm⊘ or more), a microwave integrated circuit board or impedance matching in various microwave circuits in a microwave region. The Related Art of the Invention There have been known various BaO-xTiO 2 dielectric ceramic compositions, for example, disclosed in Japanese Patent Publication No. hei 1-37807, Japanese Patent Laid-open No. sho 61-10806. Japanese Patent Laid-open No. sho 61-10807, Japanese Patent Laid-open No. sho 63-117957 and the like. However, the conventional dielectric ceramic compositions described above have the disadvantage of causing hexagonal pattern cracks on the surface of the resonator in a baking process thereby significantly reducing the yield. In particular, the large size resonator has such a tendency to be prone to the above cracks. SUMMARY OF THE INVENTION To solve the above problem, the present invention has been made, and an object is to provide a BaO-xTiO 2 dielectric ceramic composition capable of preventing hexagonal pattern cracks while achieving the practical characteristics. The present applicants have examined the mechanism for the occurrence of the hexagonal pattern cracks in the BaO-xTiO 2 dielectric ceramic composition, and consequently have found the fact that there is a correlation between the content ratio of Ba 2 Ti 9 O 20 and the occurrence of the cracks. Namely, in a preferred mode of the present invention, there is provided a BaO-xTiO 2 dielectric ceramic composition containing BaTi 4 O 9 and Ba 2 Ti 9 O 20 (X = 3.5 to 4.5), wherein the content ratio of Ba 2 Ti 9 O 20 {Ba 2 Ti 9 O 20 /(BaTi 4 O 9 + Ba 2 Ti 9 O 20 ) } obtained by a X-ray diffraction maximum peak height integration method is in the range of 0.10 to 0.19. In the above, the following five specified peak values are used in the above X-ray diffraction maximum peak height integration method: the first and second peak values respectively ascribed to the (421) face and (222) face of Ba 2 Ti 9 O 20 ; the third, fourth and fifth peak values respectively ascribed to the (200, 140) face, the (121) face, and the (230, 150) face of BaTi 4 O 9 . Thus, each maximum peak height is obtained, and thereby the content ratio of Ba 2 Ti 9 O 20 { Ba 2 Ti 9 O 20 /(BaTi 4 O 9 + Ba 2 Ti 9 O 20 ) } is calculated. In addition, the value of [0.19 ] appearing in the wording [ the content ratio of Ba 2 Ti 9 O 20 is less than 0.19] means the value obtained by the X-ray diffraction maximum peak height integration method. Accordingly, even using the same sample, in the case of obtaining the content ratio of Ba 2 Ti 9 O 20 by another method of, for example, integrating the area of the specified peak, the value of [0.19], that is, the boundary value is changeable to another value depending on the method. When the variable "x" is less than 3.5, the temperature coefficient of the resonance frequency (hereinafter, referred to as τ f ) is 50ppm/ °C or more. When the variable "x" is more than 4.5, τ f tends to approach the value of 0 but the unloaded Q (hereinafter, referred to as Qu) is reduced. Accordingly, any case is unfavorable in practical use. Also, when the content ratio of Ba 2 Ti 9 O 20 is not less than 0.19, unfavorably, there occurs the hexagonal pattern cracks. Also, the composition of the present invention may contain at least one kind of 5 to 20 pts. wt. of ZnO and 0.5 to 1 pts wt. of Ta 2 O 5 relative to 100 pts. wt. of BaO and TiO 2 . It is well known that the addition of ZnO shifts the value of τ f to the negative side while reducing the relative dielectric constant (hereinafter, referred to as ε r ). However, when the content of ZnO is less than 5 pts. wt., the above function is small and thus the value of τ f is made larger. Meanwhile, when the content of ZnO is more than 20 pts. wt., conversely, the value of τ f is made excessively small in the negative side. Also, the addition of Ta 2 O 5 is effective to improve the Qu value. When the content of Ta 2 O 5 is less than 0.5 pts. wt., the Qu value is almost similar to the case of no addition, whereas when being more than 0.5 pts. wt., the Qu value is preferably increased 1. 3 to 1.4 times as much as the case of no-addition. Also, in excess of 1 pts. wt., the additional effect is saturated. In addition, by the suitable addition of both the components, it is possible to balance the values of ε r , Qu, and τ f . Further details of the preferred embodiments are to be seen in the dependent claims The ceramic composition of the present invention may be manufactured by the steps of mixing specified starting materials at respective specified amounts and of sintering the mixture. For example, a powder to be transformed into BaO after sintering and a TiO 2 powder in respective amounts corresponding to the desired composition are mixed, calcinated and pulverized. The pulverized powder thus obtained are further mixed with a ZnO powder, a Ta 2 O 5 powder and the like in respective amounts corresponding to the desired composition, as required, and then calcinated and pulverized. The resultant calcinated powder is formed in a specified shape, and then baked. In the dielectric ceramic composition of the present invention, it is possible to prevent the occurrence of hexagonal pattern cracks and hence to improve the yield. Also, the composition of tile present invention which may contain at least one kind of 5 to 20 pts, wt. of ZnO and 0.5 to 1 pts. wt. of Ta 2 O 5 relative to 100 pts. wt. of BaO and TiO 2 , is excellent in the performances of ε r , Qu, and τ f , and has practical and balanced performance. Further, even in a large size of dielectric ceramic body having an outside diameter of 50mm⊘ or more, there occurs no cracks. Therefore, it is possible to utilize the dielectric ceramic body as a large size dielectric resonator and may be practical and excellent in quality and strength. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the result of X-ray diffraction on the surface of a sample No. 1 in Example; Fig. 2 is a graph showing the result of X-ray diffraction on the surface of a sample No. 2 in Example; Fig. 3 is a graph showing the result of X-ray diffraction on the surface of a sample No. 5 in Example; Fig. 4 is a graph showing the result of X-ray diffraction on the surface of a sample No. 8 in Example; Fig. 5 is a graph showing the result of X-ray diffraction on the surface of a sample No. 10 in Example; Fig. 6 is a graph showing the result of X-ray diffraction on the surface of a sample No. 22 in Example; and Fig. 7 is a graph showing the result of X-ray diffraction on the surface of a sample No. 23 in Example; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. The present invention will be more clearly understood with reference to the following example: [Example] (1) Preparation of Sample Powders of BaCO 3 and TiO 2 of 99.9% purity were weighed and mixed in specified amounts corresponding to each composition of [(BaO-xTiO 2 ), X; 3.8, 3,5, 4,1, 4,4]. After that, the mixture was primarily pulverized and dry mixed by a mixer, and then calcined at 1100 °C in air for 2 hrs. and pulverized, to thus manufacture the first calcinated powder. Further, in the case of further addition of powders of ZnO, Ta 2 O 5 , MnO 2 and WO 3 , as required, the ZnO powder and the like were added to the first calcined powder, and then mixed and calcined in the same manner as described above, to thus manufacture the second calcined powder. In addition, each added amount of ZnO, Ta 2 O 5 , MnO 2 and WO 3 is represented as weight (pts. wt. ) to the whole BaO-xTiO 2 (100 pts. wt.). The addition compositions are shown in Tables 1 to 3. Table 1 shows compositions where "x" is 3.8 and ZnO and Ta 2 O 5 are not present. Table 2 shows compositions where "x" is 3.5, 4.2 and 4.4. and ZnO and Ta 2 O 5 are not present. Table 3 BaO-3.8TiO 2 dielectric ceramic composition No sample(resonator) shape baking condition observed portion crack occurrence state content ratio of Ba 2 Ti 9 O 20 1 200 mm⊘ 100 mmH 1230°C × 15 hr temperature rise 15°C/hr surface hexagonal pattern crack 0.30 2 50 mm⊘ 20 mmH 1hr/charge surface OK 0.15 3 1230°C × 15 hr temperature rise 15°C/hr surface hexagonal pattern crack 0.25 4 100 mm⊘ 40 mmH 1230°C × 15 hr temperature rise 15°C/hr surface hexagonal pattern crack 0.31 5 OK 0.16 6 200 mm⊘ 100 mmH 1170°C × 8 hr temperature rise 15°C/hr surface hexagonal pattern crack 0.19 7 surface hexagonal pattern crack 0.22 8 ditto 2hrs/charge surface OK 0.14 9 ditto 4hrs/charge surface hexagonal pattern crack 0.20 10 ditto 1230°C × 7 hr temperature rise 26.4°C/hr surface OK 0.18 BaO-xTiO 2 dielectric ceramic composition No x sample shape baking condition observed portion crack occurrence state content ratio of Ba 2 Ti 9 O 20 11 3.5 200 mm⊘ 100 mmH 1330°C × 15 hr temperature rise 15°C/hr surface hexagonal pattern crack 0.28 12 ditto 1330°C × 15 hr temperature rise 17.5°C/hr surface absence 0.14 13 4.2 ditto 1240°C × 8 hr temperature rise 15°C/hr surface hexagonal pattern crack 0.38 14 ditto 1240°C × 8 hr temperature rise 17.5°C/hr surface absence 0.10 15 4.4 ditto 1220°C × 10 hr temperature rise 20°C/hr surface hexagonal pattern crack 0.42 16 ditto 1220°C × 10 hr temperature rise 25°C/hr surface absence 0.12 BaO-3.8TiO 2 dielectric ceramic composition No assistant sample shape baking condition observed portion crack occurrence state content ratio of Ba 2 Ti 9 O 20 17 ZnO 6wt.pts. 200 mm⊘ 100 mmH 1250°C × 4 hr temperature rise 20°C/hr surface absence 0.14 18 ZnO 15wt.pts. ditto 1250°C × 4 hr temperature rise 20°C/hr surface absence 0.18 19 Ta 2 O 5 0.5 wt.pts. ditto 1270°C × 4 hr temperature rise 20°C/hr surface absence 0.16 20 Ta 2 O 5 1wt.pts. ditto 1270°C × 4 hr temperature rise 20°C/hr surface absence 0.17 21 ZnO 6wt.pts. ditto 1250°C × 4 hr temperature rise 20°C/hr surface absence 0.15 Ta 2 O 5 0.5 wt.pts. ditto 1230°C × 6 hr temperature rise 25°C/hr surface absence 0.14 22 MnO 2 0.2 wt.pts. ditto 1230°C × 7 hr temperature rise 26.4°C/hr surface absence 0.15 23 WO 3 0.5 wt.pts. ditto 1230°C × 6 hr temperature rise 25°C/hr surface absence 0.15 24 MnO 2 0.2 wt.pts. WO 3 0.2 wt.pts. ditto 1230°C × 7 hr temperature rise 26.4°C/hr surface absence 0.15 25 ZnO 20wt.pts. ditto 1250°C × 4 hr temperature rise 20°C/hr surface absence 0.18 shows compositions where "x" is 3.8 and ZnO and/or Ta 2 O 5 , and further MnO 2 or WO 3 are present. The above first or second calcined powder was added with an organic binder in a suitable amount and an ion exchange water (260 to 500g), being secondarily pulverized using alumina balls of 20mm⊘, and then pelletized by spraying and drying. Subsequently, the pelletized powder was formed at a pressure of 1000kg/cm 2 into a cylindrical shape having the size corresponding to the diameter (outside diameter) and the height shown in each Table after baking (incidentally, inside diameter: changeable within the range of 10 to 60mm ⊘). Next, the compact thus obtained was baked in air under the condition shown in each of Tables 1 to 3, and finally ground in the size shown in each Table, to thus form each of sample Nos. 1 to 25. In addition, Tables 1, 2 and 3 show the results in the case that "x" of (BaO-xTiO 2 ) is [3.8], [3.5, 4.2 and 4.4] and [3.8], respectively. Further, in Table 3, ZnO, Ta 2 O 5 , MnO 2 or WO 3 is added. (2) Performance Estimation In each sample, the state of causing cracks on the surface was observed by an optical microscope and an scanning electron microscope. Further, the surfaces (upper surface and barrel surface) were subjected to X-ray diffraction, and thus the content ratio of Ba 2 Ti 9 O 20 ( Ba 2 Ti 9 O 20 /(BaTi 4 O 9 + Ba 2 Ti 9 O 20 ) } was obtained by a maximum peak height integration method. Each intensity of the X-ray diffraction was measured at room temperature under the condition that the time constant was 0.5 sec. and the rotational speed of the goniometer was 2 = 1 ° /min using a CuKα ray which was generated at a tube voltage of 50KV and a tube current of 80mA and was made to pass through a slit of 1 ° , 1 ° and 0.15mm and a Ni foil filter. In this case, as described above, With respect to Ba 2 Ti 9 O 20 , the peak intensities respectively ascribed to the (421) face and the (222) face were represented by the maximum peak heights from the background. Also, with respect to BaTi 4 O 9 , the peak intensities respectively ascribed to the (200, 140) face, (121) face and the (230, 150) face were represented by the maximum peak heights from the background. Thus, the content ratio of Ba 2 Ti 9 O 20 was obtained by the following equation: Content of Ba 2 Ti 9 O 20 = (I (421) + I (222) )/(I (421) + I (222) + I (200,140) + I (121) + I (230,150) ) The calculation of the above content ratio on the basis of, for example, the result shown in Fig. 4 is as follows: content ratio of Ba 2 Ti 9 O 20 = (A1 peak height + A2 peak height)/(A1 peak height + A2 peak height + B1 peak height + B2 peak height + B3 peak height) . These calculated results are shown in Tables 1 to 3. Also, the graphs showing the results of X-ray diffraction on the sample Nos. 1, 2, 5, 8, 10, 22 and 23 are shown in Figs. 1, 2, 3, 4, 5, 6 and 7, respectively. Characteristics of BaO-xTiO 2 dielectric ceramic composition No sintered density (g/cm 3 ) relative dielectric constant ε r Qu value (4.5GHz) temperature coefficient of resonance frequency τ f (ppm/°C) 2 4.692 34.5 4100 0 12 4.609 39.2 3060 +16.2 17 4.682 36.0 3100 +6.0 18 4.694 33.8 3200 0 20 4.690 38.5 4000 +18.0 21 4.658 35.8 3250 +6.8 22 4.698 34.6 4100 0 23 4.690 34.5 4300 0 24 4.608 34.5 4300 0 25 4.703 33.0 3000 -8.4 Further, in each sample shown in Table 4, sintered density was measured by an Archimedes' method, and also the values of ε r , Qu, and τ f are measured by a parallel conductive plate type dielectric cylinder resonator method (TE 0 11 mode). The results are shown in Table 4. In addition, the resonance frequency lies near 4.5GHz. As a result, there occurs hexagonal pattern cracks for the content ratio of Ba 2 Ti 9 O 20 not less than 0.19; but there occurs no hexagonal pattern crack for that less than 0.19. Even in a cylindrical sample having an outside diameter of 50mm ⊘ or more, particularly, of 200mm⊘, there occurs no cracks. In the terms of this point, the ceramic composition of the present invention is highly excellent in quality as compared with the conventional one. Also, even in the further larger size ceramic composition having an outside diameter of 280mm⊘ and a height of 130 to 140mm, there occurs no crack. In addition, as shown in Table 1, Ba 2 Ti 9 O 20 is a high temperature stable phase as compared with BaTi 4 O 9 , and thus tends to be excessively baked, and consequently Ba 2 Ti 9 O 20 is increased which promotes the tendency of causing the hexagonal pattern cracks. Also, it is considered that the occurrence ratio of Ba 2 Ti 9 O 20 is related to the heat quantity in high temperatures including not only the baking temperature (maximum value) and holding time but also the temperature rising speed. Further, as shown in Table 4, each sample is excellent in the balance of the performances. Particularly, the following samples are preferable: ZnO (Nos. 17, 18 and 25); Ta 2 O 5 (No. 20); ZnO and Ta 2 O 5 in suitable amounts respectively (No. 21); MnO 2 (No. 22), WO 3 (No. 23); and MnO 2 and WO 3 (No. 24) in a suitable amount. Also, each of the sample Nos. 22, 23 and 24 has the large sintered density, and is excellent in degree of sintering. Further, by addition of ZnO, it is possible to freely adjust the τ f , particularly, to be a small value near 0. The above samples are practical because of causing no crack and being excellent in the practical performances. In addition, the present invention is not limited to the above example; but may be variously modified according to the objects and applications within the scope of the present invention. Namely, the baking temperature, baking time, temperature rising speed and the like may be variously modified. Also, the starting material for producing BaO may includes peroxide, hydroxide and nitrate and the like other than the above BaCO 3 . Further, by use of a sintering assistant (for example, at least one kind of MnO 2 , WO 3 , ZrO 2 , SnO 2 and the like), it is possible to improve the degree of sintering while keeping the above dielectric ceramic characteristics and preventing the occurrence of cracks.

Claims: A dielectric ceramic composition comprising Ba0-xTi0 2 , wherein x is 3.5 to 4.5, containing BaTi 4 0 9 and Ba 2 Ti 9 0 20 , having a ratio of 0.10 ≦ Ba 2 Ti 9 O 20 BaTi 4 O 9 + BA 2 Ti 9 O 20 < 0.19 wherein Ba 2 Ti 9 0 20 is the peak height of the (421) face + the peak height of the (222) face of Ba 2 Ti 9 0 20 , and BaTi 4 0 9 is the peak height of the (200,140) face + the peak height of the (121) face + the peak height of the (230,150) face of BaTi 4 0 9, said ratio being obtained by an X-ray diffraction maximum peak height integration method. The dielectric composition of claim 1, wherein said ratio is in the range of 0.10 to 0.18, the dielectric constant is 34.5 to 39.0, the Qu value (4.5 GHz) is 3200 to 4100, and the temperature coefficient of the resonance frequency is 0 to +10 ppm/°C. The dielectric ceramic composition of claim 1 or 2, further comprising at least one of Zn0 and Ta 2 0 5 , wherein the content of Zn0 is 5 to 20 parts by weight and/or the content of Ta 2 0 5 is 0,5 to 1 parts by weight, relative to 100 parts by weight of Ba0 and Ti0 2 . The dielectric ceramic composition of claim 3, wherein said ratio is in the range of 0.10 to 0.18, the dielectric constant is 33.8 to 38.5, the Qu value (4.5 GHz) is 3100 to 4000, and the temperature coefficient of the resonance frequency is -9 to +10 ppm/°C. The dielectric ceramic composition of any of claims 1 to 4, which contains at least one sintering assistant selected from Mn0 2 , WO 3 , Zr0 2 and Sn0 2 . The dielectric ceramic composition of any of claims 1 to 5, which has the form of a cylindrical body having an outside diameter of 50 mm or more. The dielectric ceramic composition of claim 6, wherein the diameter of said cylindrical body is 50 to 200 mm.

Inventors: MIZUNO FUMIO, SATO MANABU, MIZUNO, FUMIO, SATO, MANABU, Mizuno, Fumio, c/o NGK Spark Plug, Co., Ltd., Sato, Manabu, c/o NGK Spark Plug, Co., Ltd.
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO., LTD
Application year: 1992
Main classification: C04B35
IPC codes: H01B3, C04B35