Optically  clear,  as  visually  observed,  natural

quartz  crystals  of  Brazilian  and  Arkansas  origins,  which exhibit  Al–OH–-centers  in  their  as-received  conditions,have been measured for their low temperature ESR spectra to  see  the  presence  of  Al-hole  centers.  The  ESR  spectra revealed   the   presence   of   Al-hole   centers   in   their   as-received  conditions.  These  centers  showed  an  increase  in their  strength  upon  irradiation  with  a 60 C0  source.  Such observations were exhibited by Al–OH-centers as noticed earlier. The crystals were thus noticed to exhibit the presence  of  Al–OH– -centers  and  also  Al-hole  centers  in  their

as-received  conditions.  The  observations  match  with  the results  on  cultured  quartz  where  irradiation  breaks  away the  Al-alkali  centers  into  a  mixture  of  Al–OH–-  and  Al-hole centers. It is thus concluded that the natural crystals,which  exhibit  the  presence  of  these  centers  in  their  as-received  condition,  have  been  irradiated  in  nature  with  a low dose

Bahadur, Harish

Tissoux, Helene

Toyoda, Shin

Usami, Teruo

IR@NPL

Radiation effects in natural quartz crystalsHarish Bahadur Æ He´le`ne Tissoux Æ Teruo Usami ÆShin ToyodaReceived: 15 May 2007 / Accepted: 20 August 2007 / Published online: 25 September 2007 Springer Science+Business Media, LLC 2007Abstract Optically clear, as visually observed, naturalquartz crystals of Brazilian and Arkansas origins, whichexhibit Al–OH–-centers in their as-received conditions,have been measured for their low temperature ESR spectrato see the presence of Al-hole centers. The ESR spectrarevealed the presence of Al-hole centers in their as-received conditions. These centers showed an increase intheir strength upon irradiation with a 60C0 source. Suchobservations were exhibited by Al–OH–-centers as noticedearlier. The crystals were thus noticed to exhibit the pres-ence of Al–OH–-centers and also Al-hole centers in theiras-received conditions. The observations match with theresults on cultured quartz where irradiation breaks awaythe Al-alkali centers into a mixture of Al–OH–- and Al-hole centers. It is thus concluded that the natural crystals,which exhibit the presence of these centers in their as-received condition, have been irradiated in nature with alow dose.1 IntroductionAlpha quartz continues to be of scientific interest. Themajor stimulus in research in quartz crystals is due tothe varied technological applications for which quartzis uniquely suited, such as in optics, clocks formicroprocessors, temperature and mass sensors, acceler-ometers, and a variety of electronic devices includingcrystal oscillators and filters for precision frequency con-trol, communications and generally in signal processing incomputers. Recent development of Quartz Crystal Micro-balance (QCM) has added a new dimension to theapplication of quartz crystals wherein almost every con-ceivable aspect in the analytical measurements can beperformed by using a quartz crystal resonator. In thepresent day technology, the name ‘Quartz’ has become asymbol of quality for a variety of precision equipment.Until about a half century before, the use of quartz crystalin industry was mainly supported by the ready availabilityof large amount of single optical grade natural quartzmaterial. Continued efforts on hydrothermal synthesis ofcultured quartz during last over four decades have come toa stage that much of the present industrial demand of quartzcrystal is satisfied by the man made material except wherea radiation-resistant quartz is required for aerospaceapplications. It would thus be technologically veryimportant to process quartz crystals for their low radiation-sensitivity.The presence of impurities in quartz, such as aluminum,alkalis like Na or Li and also hydrogen, limits the Q(quality factor) and therefore affect nearly every applica-tion of it as a device. Because of its various technologicalapplications, quartz is also grown in the laboratory undercontrolled conditions for specific applications. Addition-ally, some post growth treatment may also be given toquartz stone which may change its composition for somespecial applications. The cultured quartz is grown hydro-thermally and therefore hydrogen is an ubiquitous impurityin quartz. Further, natural quartz is almost always used asthe starting material for the hydrothermal synthesis ofcultured quartz. Thus, the natural quartz continues to be aH. Bahadur (&)National Physical Laboratory, New Delhi 110012, Indiae-mail: hbahadur@mail.nplindia.ernet.inH. Tissoux  T. Usami  S. ToyodaDepartment of Applied Physics, Okayama University of Science,Okayama 700-0005, Japan123J Mater Sci: Mater Electron (2008) 19:709–713DOI 10.1007/s10854-007-9388-0subject matter of serious scientific study. Point defects innatural and cultured quartz have been have been underinvestigation for over five decades. Still, there remains a lotto investigate for corroborating the various complex issuesrelating to these defects and their role in the device per-formance. Much of our present day understanding hascome from the study of radiation effects and monitoring thespectroscopic signals coming from the radiation-inducedchanges in the configuration of point defects of the post-irradiated quartz. An analysis of the signal from the post-irradiated defects helps in deriving the structure of theirprecursors. It is known [1–7] that each quartz has trivalentaluminum (as Al3+) at substitutional sites of Si4+. Theelectron excess defect of Al3+ center is compensated by thepresence of interstitial monovalent impurity either alkalis(M+) such as Na+, Li+, or protons near aluminum in theopen c-axis channels parallel to the growth direction of thecrystals. When exposed to ionizing radiation, the Al–M+centers break away into a mixture of Al-hole and Al–OH–-centers [1–7].We present here results of our further investigations onnatural quartz crystals of Arkansas and Brazilian origins.These crystals are those on which near infrared investiga-tions coupled with sweeping and irradiation have beenreported earlier in many publications [8–13]. These crystalshave nearly same concentration of aluminum impurity buthave widely different H-levels. The Arkansas quartz haslow-H while Brazilian quartz has high-H levels. In the as-received conditions, both the crystals showed the presenceof Al–OH–-centers [8–13].We expect that the natural irradiation could be one ofthe causes to produce the Al–OH centers in natural crys-talline quartz. Additionally, if the Al–OH–-centers areformed due to irradiation, it should be accompanied by theAl-hole centers as well. This expectation has been verified.2 Experimental procedureNatural quartz crystals were investigated in their as-received condition and after irradiation with an accumu-lated dose of 1.21 kGy. The dose rate was 3.0 C/kgh(101 Gy/h) of 60C0 source at Takasaki Research Instituteof Japan Atomic Energy Research Institute. The electronspin resonance method was used to detect the presence ofAl-hole centers in these samples of quartz crystals. Mea-surements were done at liquid nitrogen temperatures tomonitor the impurity-related defects. The ESR spectrom-eter, JEOL PX 2300 of Okayama University of Science,Okayama, Japan was used. The crystals were crushed,powdered, and sieved through a mesh of less than 217 lmand greater than 140 lm. The particles in this size rangewere collected. A quantity of 100 mg of both the samplesof Brazilian and Arkansas quartz was collected in a glasstube which was transferred to the microwave cavity of thespectrometer for the measurements.3 Results and discussionAs mentioned before, the crystals studied in the presentwork have been studied earlier [8–13] for their radiationeffects using near infrared absorption spectroscopy. For aready reference, Fig. 1 shows the near IR spectra for boththe crystals in their as-received condition. In the figure, thebands at 3,367 and 3,306 wave numbers are known to bedue to the presence of Al–OH–-centers with proton locatedat long- and short-Al–O bonds, respectively. Many of theother bands still remain unidentified. Irradiation effects onthese crystals were studied [10–13] by irradiating them at77 K before and after 300 K. It was noticed that the77 K-irradiation did not increase the strength of Al–OH–-centers but in most cases transferred the protons from thelong bond Al–OH– to the short-bond to Al–OH– so thatboth the bands become equally populated with protons.There was however, no net increase of Al–OH–-centers at77 K irradiation. This was so because at this temperature,the alkalis from the aluminum centers would not be able tomove away so that protons may replace them. Upon irra-diation at 300 K, these crystals showed an increase in theAl–OH–-centers. This was due to breakaway of Al-alkalicenters into a mixture of Al-hole and Al–OH–-centers. Onthe other hand, in the case of cultured quartz (such as inFig. 2), there is no evidence of Al–OH–-centers in the as-grown condition. It is known [4] that the Al–OH–-centersin cultured quartz can be produced either by sweeping inH-ambient or by irradiation beyond 200 K. In the case ofFig. 1 Near IR spectra of natural quartz crystals of Brazilian andArkansas origin in their as-received conditions (after Bahadur [9]). Itmay be noticed that the bands at 3,367 and 3,306 wave numbers occurin their as-received (or as-grown) conditions710 J Mater Sci: Mater Electron (2008) 19:709–713123sweeping of cultured quartz, the protons from the H-ambient will get trapped at Al-sites to replace alkalis whichhave moved from Al centers during sweeping under theeffect of electric field and the high temperature. If thesweeping is complete, all the Al-alkali centers will getconverted to Al–OH– because all the aluminum ions will becharge compensated with protons. In such a case, there willnot be any permanent effect of 300 K-irradiation [5]. In thecase of natural quartz also, H-sweeping increases thestrength of Al–OH–-centers to the maximum to compensateall aluminum with protons if the sweeping is complete [9,10]. In both the cases of natural as well as cultured quartz,the Al-hole centers will not be produced by sweeping underH-ambient. The Al-hole centers get produced only whenthe quartz is irradiated at temperatures beyond 200 K. Thiscenter is usually observed by ESR techniques. The lineshape of the ESR signal depends upon the crystal sym-metry and orientation with respect to the magnetic field[14, 15]. A representative ESR spectrum of quartz for theAl-hole centers for a crystalline quartz parallel to themagnetic field [6] is shown in Fig. 3. For a powderedquartz samples [16, 17], Fig. 4 depicts a representativeESR spectrum. In the ESR spectra of Al-hole centers inquartz crystals, a number of hyperfine lines are observed[14, 15, 18–20] due to the nuclear spins and quadruplesplitting Q[Iz2–(I/3)(I + 1)] of 27Al. Figures 5 and 6 depictthe ESR spectra in quartz samples corresponding to the Al-hole centers of Brazilian and Arkansas origin respectivelyobserved at 80 K in their as-received conditions. The nearIR spectra for these crystals in their as-received conditionsare shown in Fig. 1. These spectra also show the presenceof Al–OH–-centers in them in their as-received conditions.Figures 7 and 8 show the expanded view of the ESRspectra for the Al-hole centers taken from Figs. 5 and 6,respectively. The occurrence of Al-hole centers, asobserved in the ESR spectra and Al–OH–-centers asobserved in their near infrared spectra, in their as-receivedcondition suggests that the crystals have received theradiation dose. The source of radiation could perhaps besome radioactive element in the vicinity of the locationwhere these crystals were grown in nature.We have investigated the effect of irradiation on theAl-hole centers on these crystals. As mentioned earlier, theirradiation facility of 60C0 source at Takasaki ResearchInstitute of Japan Atomic Energy Research Institute wasused. The dose rate was 3.0 C/kgh (101 Gy/h). The crystalswere irradiated for the maximum dose of 1.21 kGy. Fig-ures 9 and 10 and depict the results for the Brazilian andArkansas samples after irradiation with a dose of 1.21 kGy.As expected, it was noticed that the strength of the Al-holecenters increased after irradiation. It has been describedearlier [1–8] that the Al–OH–-centers also show an increaseafter irradiation.Fig. 2 Near IR spectra of cultured quartz crystal in its as-growncondition. It may be noticed that there is no appearance of the bandsat 3,367 and 3,306 wave numbers in its as-received or as-growncondition (after Bahadur [8])Fig. 3 ESR signal of Al-hole centers for a quartz crystal withmagnetic field parallel to c-axis (after Halliburton et al. [6])Fig. 4 The low temperature (*77 K) ESR spectrum of powderednatural quartz samples representing the Al-hole centers (after Toyoda[16])J Mater Sci: Mater Electron (2008) 19:709–713 711123It is important to note here that here that the culturedcrystals do not show the evidence of Al–OH–-centers intheir as-grown conditions (Fig. 2). Thus, in the as-growncultured quartz, none of the aluminum centers are com-pensated with protons. However, when the cultured crystalare irradiated, the Al–OH–- and Al-hole centers are formedwhich can be monitored by near infrared absorption andESR techniques respectively. In general, the formation ofAl–OH–- and Al-hole centers occur simultaneously whenthe Al-alkali centers break away under the influence ofFig. 5 The ESR spectrum of the Brazilian quartz crystals in itsas-received condition observed at 80 K. The spectrum represents thequadruple splitting of 27Al nuclei. In addition, a strong signalcorresponding to the spectrum of E10is seen in this case alsoFig. 6 The ESR spectrum of the Arkansas quartz crystals in its as-received condition observed at 80 K. The spectrum represents thequadruple splitting of 27Al nuclei. In addition, a strong signalcorresponding to the spectrum of E10is also seenFig. 7 Expanded view of the ESR spectrum of Al-hole centers in theas-received Brazilian quartz samples for which the complete spectrumis shown in Fig. 5Fig. 8 Expanded view of the ESR spectrum of Al-hole centers in theas-received Arkansas quartz samples for which the complete spectrumis shown in Fig. 6Fig. 9 ESR spectrum for the Al-hole centers in the Brazilian naturalquartz after irradiating at 300 K with a dose of 1.21 kGy. Thespectrometer parameters were; Microwave Fre-quency = 8934.143 MHz, Mod. Freq. = 100 kHz modulationwidth = 0.1 mT, time const. = 0.03, microwave power = 5 mW,sweep time = 30 s. CH1 amplitude = 1,000712 J Mater Sci: Mater Electron (2008) 19:709–713123irradiation. Both types of crystals, when swept in hydrogenatmosphere show only an increase of Al–OH centers. Insuch a case, the protons from the ambient replace alkalis,mostly Li in cultured crystals and some Na also in the case ofnatural crystals. That the Na is present in natural quartz hasbeen observed by the acoustic loss measurements of Martin[1, 2]. The present results confirm that the formation ofAl-hole in natural quartz also proceeds in the way as in thecase of high purity cultured quartz, where irradiation breaksaway the Al–M+ centers into a mixture of Al-hole andAl–OH–-centers [3–7]. Our measurement show that thesecrystals have received natural radiation during growth. Dosedependence of these centers will be reported later.4 Summary and conclusionsWe have investigated natural visually optically quartzcrystals of Brazilian and Arkansas origins. These crystalswere earlier studied for the near infrared absorption mea-surements and exhibited the presence of Al–OH–-centerswhich increased upon irradiation. In the present work, wehave investigated the presence of Al-hole in these crystalsin their as-received condition and after irradiation. Thecenters were found to show an increase after irradiation. Adiscussion has been presented which supports the view thatthe natural crystals showing the presence of Al–OH–-cen-ters in their as-received condition have received a radiationdose during their growth. This was verified by the presenceof Al-hole centers in their as-received condition. Thus, ashas been established for the cultured quartz that Al-alkalicenters break away under the influence of radiation into amixture of Al-hole and Al–OH–, the mechanism is alsoapplicable for natural quartz as well. The only differencebetween the natural and cultured quartz appears to beforthcoming is that while it is important to irradiate cul-tured quartz in laboratory for producing the Al-hole andAl–OH–, such centers in natural quartz exist because theyalready have received the irradiation in nature.Acknowledgments The authors are thankful to Dr. Vikram Kumar,Director, National Physical Laboratory, New Delhi for his encour-agement in the work and Okayama University of Science for thesupport. This work was also supported by the Japan Society forpromotion of Science (JSPS) by way of an award of invitation fel-lowship to Harish Bahadur. He´le`ne Tissoux was a JSPS post doc atOkayama University of Science. T. Usami is a research studentsupported by JSPS at OUS. The authors also thank Professor JoelMartin of Oklahoma State University and Dr. J.C. King of SandiaNational Laboratories, Albuquerque, NM (now retired) for the gift ofArkansas and Brazilian crystals and their encouragement to investi-gate natural quartz.References1. J.J. Martin, J. Appl. Phys. 56, 2536 (1984)2. J.J. Martin, in Proceedings of the 38 th Annual Frequency Con-trol Symposium (1984), p. 16. Copies available from NationalTechnical Information Service (NTIS), 5285 Port Royal Road,Sills Bldg., Springfield, VA 221613. L.E. Halliburton, J.J. Martin, W.A. Sibley, in Study of DefectsProduced by Growth, Post Treatment and Fabrication of Quartz(Oklahoma State University, RADC-TR-81-276, Oct. 1981).Copies available from Rome Air Development Command,Hanscom, AFB, MA 017314. L.E. Halliburton, N. Koumvakalis, M.E. Markes, J.J. Martin, J.Appl. Phys. 52, 3565 (1981)5. L.E. Halliburton, Cryst. Lattice Defects Amorph. Mater. 12, 163(1985)6. L.E. Halliburton, M.E. Markes, J.J. Martin, in Proceedings of the34th Annual Frequency Control Symposium (1980), pp. 1–8.Copies available from National Technical Information Service(NTIS), 5285 Port Royal Road, Sills Bldg., Springfield, VA221617. J.J. Martin, B.H. Hwang, H. Bahadur, G.A. Berman, J. Appl.Phys. 65, 4666 (1989)8. H. Bahadur, J. Appl. Phys. 66, 4973 (1989)9. H. Bahadur, J. Appl. Phys. 73, 7790 (1993)10. H. Bahadur, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 41,820 (1994)11. H. Bahadur, J. Appl. Phys. 75, 1421 (1994)12. H. Bahadur, IEEE Trans. Nucl. Sci. 39, 2170 (1992)13. H. Bahadur, IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 47,1190 (2000)14. R.H.D. Nuttall, J.A. Weil, Can. J. Phys. 59, 1696 (1981)15. R.H.D. Nuttall, J.A. Weil, Can. J. Phys. 59, 1709 (1981)16. S. Toyoda, in Production and Decay Characteristics of Para-magnetic Defects in Quartz: Applications to ESR Dating. Ph.D.Thesis, Osaka University, Toyonaka, Osaka, Japan, 199217. M. Ikeya, in New Applications of Electron Spin Resonance,Dating, Dosimetry and Microscopy (World Scientific, Singapore,New Jersey, London, Hong Kong, 1993)18. M.C.M. O’Brien, M.H.L. Pryce, in Defects in Crystalline Solids(Bristol Conference, London, Phys. Soc. London, England,1955), p. 8819. M.C.M. O’Brien, Proc. R. Soc. Lond. A231, 404 (1955)20. J.A. Weil, Phys. Chem. Minerals 10, 149 (1984)Fig. 10 ESR spectrum for the Al-hole centers in the Arkansas naturalquartz after irradiating at 300 K with a dose of 1.21 kGy. Thespectrometer parameters were identical as for the Fig. 9 except for theCH1 amplitude set at 700J Mater Sci: Mater Electron (2008) 19:709–713 713123

Radiation effects in natural quartz crystals

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