Barium Manganese Fluoride, a New Crystal for Microwave Ultrasonics

Spencer, E. G.; Guggenheim, H. J.; Kominiak, G. J.

doi:10.1063/1.1653410

Cited by 41 publications

(7 citation statements)

References 4 publications

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“…And even when they do signal a phase transition, its nature is not revealed in any direct way. A rather good example in ferroelectrics is the work of Spencer and Kominiak [6] on the antiferroelectric incommensurate transition in BaMnF 4 [7,8]. Their ultrasonic data were for some years the only evidence of a phase transition, and such skepticism surrounded these data that they were not cited in subsequent work on BaMnF 4 from the same laboratory.…”

Section: Ultrasonic Techniquesmentioning

confidence: 95%

Interpretation of elastic anomalies in SrTiO3 at 37K

Scott

Ledbetter

1997

Zeitschrift für Physik B Condensed Matter

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Section: Ultrasonic Techniquesmentioning

confidence: 95%

Interpretation of elastic anomalies in SrTiO3 at 37K

Scott

Ledbetter

1997

Zeitschrift für Physik B Condensed Matter

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“…The melting temperatures range between 720 and 965°C; the Curie-Weiss temperatures can be extrapolated from the temperature dependence of the dielectric constants and range between 810 and 1320°C. 11 In BaMnF 4 an additional structural phase transition occurs at ϳ255 K. 12 The resulting low-temperature structure is incommensurate along the c axis. 13 To facilitate a systematic comparison between the different BaMF 4 systems we do not consider this low-temperature structure of BaMnF 4 in the present study and instead use perfect Cmc2 1 symmetry for all systems.…”

Section: Introductionmentioning

confidence: 99%

Origin of ferroelectricity in the multiferroic barium fluoridesBaMF4: A first principles study

2006

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We present a first-principles study of the series of multiferroic barium fluorides with the composition BaMF 4 , where M is Mn, Fe, Co, or Ni. We discuss trends in the structural, electronic, and magnetic properties, and we show that the ferroelectricity in these systems results from the freezing in of a single unstable polar phonon mode. In contrast to the case of the standard perovskite ferroelectrics, this structural distortion is not accompanied by charge transfer between cations and anions. Thus, the ferroelectric instability in the multiferroic barium fluorides arises solely due to size effects and the special geometrical constraints of the underlying crystal structure.

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“…For a(T)> 0 the equilibrium of the system is at Qi 0= #2 0==0 > while for «(T)<0 there are two possible situations depending on the relative magnitudes ofb 1 …”

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confidence: 97%

“…1 Ryan and Scott 2 investigated the transition by Raman scattering and showed that it is antiferrodistortive and involves a doubling of the unit cell. Recently the author 3 reported ultrasonic velocity measurements for the pure modes propagating along the principal axes and showed that there are sharp velocity dips for the longitudinal mode propagating along the c axis (v cc ) and for the shear mode propagating along the c (orb) axis and polarized along the b (or c) axis {v ch = v bc ).…”

mentioning

confidence: 99%

“…The purely elastic part of the free energy involving the coupled strains only is ^^i)=i(Ci^i 2 + C 22^2 2 +C 33^3 2 + C 44 x 4 2 ) + C 12 x 1 x 2 + C 13 x 1 x 3 + C 23 x 2 x 3 . (1) To minimize the total free energy, which is the sum of Eqs. (1), (6), and (7), the usual procedure 11 of first minimizing with respect to the strain variables and then eliminating the strains and minimizing with respect to the Q x may be followed.…”

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confidence: 99%

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Ultrasonic Attenuation and Mechanism for the 250°K Antiferrodistortive Transition in BaMnF4

Fritz¹

1975

Phys. Rev. Lett.

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Critical attenuation measurements are reported for two anomalous acoustic modes near the 250°K transition of BaMnF 4 . A mechanism for the transition involving rotations of the MnF 6 octahedra about the orthorhombic b axis is proposed, with a pair of phonons at the Brillouin zone S points 7r(0,1/6 ,± 1/c) being the soft modes. This mechanism, which suggests strong two-dimensional correlations, appears consistent with previous work on BaMnF 4 as well as with the ultrasonic data.I report here measurements of ultrasonic attenuation in the vicinity of the 250°K antiferrodistortive transition of BaMnF 4 . These yield the first determination of critical attenuation exponents for an antiferrodistortive transition in a material not of the perovskite structure and thus provide a new test of recent general theories of ultrasonic anomalies associated with this important class of structural phase transitionSo I also present a proposed mechanism for the transition which appears consistent with the experimental work done so far on BaMnF 4 . In particular, this mechanism suggests critical fluctuations which are strongly correlated in two dimensions, and this provides an explanation for the observed longitudinal-mode attenuation exponent being significantly larger than in the perovskites.The 250°K transition was first observed in ultrasonic attenuation studies by Spencer, Guggenheim, and Kominiak. 1 Ryan and Scott 2 investigated the transition by Raman scattering and showed that it is antiferrodistortive and involves a doubling of the unit cell. Recently the author 3 reported ultrasonic velocity measurements for the pure modes propagating along the principal axes and showed that there are sharp velocity dips for the longitudinal mode propagating along the c axis (v cc ) and for the shear mode propagating along the c (orb) axis and polarized along the b (or c) axis {v ch = v bc ). There has not been a direct experimental determination of the structure of the low-temperature phase, so that the actual mechanism of the transition is not established.In the present work the attenuation of the two modes with sharp velocity anomalies was measured by the pulse-echo technique for temperatures between 190 and 300°K. Within about 0.5°K of the transition the data exhibit rounding effects, presumably due to sample imperfections. 4 Data were obtained at frequencies between 14 and 90 MHz. For the shear mode (a cb ) data were obtained and analyzed both above and below the transition temperature T 0 . For the longitudinal mode (a cc ) the data could only be analyzed above T 0 because of domain effects below T Q0 Typical critical attenuation data are shown in Fig. 1, which is a log-log plot of the longitudinalmode critical attenuation versus reduced temperature e for T > T 0 . The critical attenuation exponent rj defined by a =A (co)e T) is r) = ^7 CC > = 2.2 ± 0.3. The frequency dependence A(w) of the attenuation (at fixed temperature) does not appear to follow 50

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Barium Manganese Fluoride, a New Crystal for Microwave Ultrasonics

Abstract: Frequency and temperature dependence of the microwave elastic properties and the velocities of propagation are reported for BaMnF4. A sharp anomaly in attenuation indicates that a crystallographic phase transition occurs at T=255°K.

Cited by 41 publications

References 4 publications

Interpretation of elastic anomalies in SrTiO3 at 37K

Interpretation of elastic anomalies in SrTiO3 at 37K

Origin of ferroelectricity in the multiferroic barium fluoridesBaMF4: A first principles study

Ultrasonic Attenuation and Mechanism for the 250°K Antiferrodistortive Transition in BaMnF4

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