Measurements of dielectric properties, pyroelectricity, and the electron paramagnetic resonance spectrum of Gd3+ as a function of temperature have been used to examine the phase transitions in CsPbCl3. The results indicate the presence of five phase transitions and the loss of a center of symmetry at 194 K. The results together with the apparent order of the transitions, and published data, enable the Landau criterion to be used so that the point group of each phase may be identified. A reasonable choice of space group is also made.
We re port on the pre paration of a sta ndard re fe re nce ma te ri a l (S RM) , mad e of s ing le-crystal c hromium-doped corundum (synth e ti c ruby), for use as a n in te ns it y s tandard in e lectron param agne ti c reso nan ce (EPR) ex pe rim e nt s . Th e S B.M ca n be used to measure, b y compari son, th e number of SI)ins in an unknown tes t sa mpl e.We se lecte d the above mat e ria l for the s tanda rd because its magne tic resona nce prope rti es are we ll understood and because it is phys ica ll y and c he mi ca ll y stab le und e r common laboratory condit ion s. To pre pa re sa mpl es whi c h ga ve sa ti s factory EPR s igna ls, it was necess ary to perform annea lin g and chemi ca l etchin g afler cUllin g. This removed strain s and surface damage. Aft er trea tm ent, th e C,':3+ resonance lin es we re sharper and th e int ensiti es we re in good ag reeme nt with the theore ti ca ll y predi c ted va lues. To a id in app lica ti on, th e theore ti ca l resona nce fi e ld s a nd li n e int e ns iti es we re ca lc ul ated and tabulated for arbi trary ori entation s ortlle sa mpl e, at se vera l com monl y used mi crowave frequ encies . Th e concentrat ion of C,"+ in the sa mpl es was de te rmin ed by measure me nt of th e sta ti c suscep ti bilit y. A quantitative EPR int ensit y ex perim ent , ba sed on measurin g th e mi crowav e power absorbed during reso nance, gave th e sa me conce nt ra tion . This proves, th at within ex perim enta l errol' th e EPR ex pe rime nt de tec ts a ll th e C ,~+ ion s in the sa mpl e, whi c h mak es the ru by a usefu l S RM.Key word s: Ab solute mea surement ; inte nsit y stalld ard ; para magnet ic reso ll ance; sp in con centra ti on; s tand a "d refe re nce mate ri a l (SRM); ruby.
Single crystals of TiC>2:Cu 2+ have been investigated at 20 K using the technique of electron paramagnetic resonance. The major features of the EPR spectra can be attributed to divalent copper (3d 9 ) in substitutional (Ti 4+ ) sites. Information has been gained about both isotopes of copper and about the interactions which concern this ion. For the substitutional site, the spin-Hamiltonian parameters in the S=i, / = f manifold are: g x =2.109, &, = 2.094, g z = 2M6, A x *= + 18.7X10" 4 cm" 1 , A y ™= +27.2X10" 4 cm" 1 , A t * = -87.5X10-4 cm" 1 , A x^= +18.8X10" 4 cm" 1 , A v « b = + 28.7XK)-4 cm" 1 , A z **= -93.7X10" 4 cm" 1 , P x = -2.56X 10~4, P v =-2.37X 10~4, and P z = +4.93X 10~4 cm' 1 . The magnitudes and relative signs of these parameters have been determined experimentally, while the absolute signs have been predicted theoretically from a model which gives a consistent picture of the ordering of the d 9 electronic states. In addition, the theoretical treatment gives a satisfactory estimate of P. Departure from tetragonality was taken into account. The covalency parameter a 2 which measures the fraction of the hole wave function on the Cu 2+ ion is found to be 0.71, and the factor K giving rise to isotropic hyperfine structure is found to be 0.31.
The electron-spin-resonance spectrum of Mo 6+ in the host lattice of Ti02 was determined. Both the hyperfine lines due to the coupling with Mo nuclei, and the superhyperfine lines due to the coupling with the next nearest neighbors, Ti nuclei, were observed. The sign of the g factor of Mo 5+ was found to be positive by observing the resonance with circularly polarized microwave radiation. The theory of Bleaney and O'Brien cannot be applied in this case, probably because the crystalline field is not strong enough and/or covalent bonding is appreciable.
This publication contains the analyses of three surveyquestionnaires to assess the needs and markets for standards in Raman spectroscopy, electron paramagnetic resonance, and magnetic moment measurements. These analyses give the requirements and suggest the strategies to be followed for making each of the above three measurement methods more quantitative than they are at present.Some of the requirements are data cataloging, standards for data presentation, standard reference materials, and standard reference data.
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