Electrical and magnetic properties of La1-xAgxMnO3 (0 ≤ x ≤ 0.5) polycrystalline ceramics by combination of first principles calculations and experimental methods

Article abstract of DOI:10.1016/j.jallcom.2019.151709

In this work, electrical and magnetic properties of La_1-xAg_xMnO₃ (LAMO, 0 ≤ x ≤ 0.5) polycrystalline ceramics with double?exchange (DE) effect and Jahn?Teller (JT) distortion were studied using a combination of first principles calculations and experimental methods. The GGA + U method was used to correct the self-interaction error (SIE) that was encountered in first principles calculations. With the increasing of Ag, energy band gaps (E_i or E_d) of LAMO ceramics and the JT effect decreased, while the DE effect was enhanced. LAMO polycrystalline ceramics (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by conventional sol?gel method in order to verify the calculation results. The X?ray diffraction revealed that the structure of LAMO ceramics transformed from single phase to multiphase as x was increased. The ρ?T curves suggested that the metal to insulator transition temperature (T_p) and DE effect were improved as x increased, which was in good agreement with the first principles calculations. In addition, the temperature coefficient of resistance (TCR) at the peak temperature (T_k) and magnetoresistance (MR) at the peak temperature (T_m) were obtained with different x. For x = 0.5, the value of TCR and MR reached 8.58% K^?1 and 21.6%, and the T_p, T_k and T_m were 304, 291 and 298 K, respectively, implying that the electrical and magnetic devices of LAMO ceramics could operate at room temperature (300 K). XPS results indicated that the concentration of Mn⁴⁺ ion increased with increasing x. The ratio of Mn⁴⁺/Mn³⁺ reached 1 ∶ 2, which had the strongest DE and magnetoelectric coupling effect for x = 0.5.

Full text of DOI:10.1016/j.jallcom.2019.151709

Journal Pre-proof
Electrical and magnetic properties of La Ag MnO (0 ≤ x ≤ 0.5) polycrystalline
-x
1
x
3
ceramics by combination of first principles calculations and experimental methods
Shuai Zhang, Tao Sun, Fuquan Ji, Gang Dong, Yang Liu, Zhidong Li, Hui Zhang,
Qingming Chen, Xiang Liu
PII:
S0925-8388(19)32942-1
DOI:
https://doi.org/10.1016/j.jallcom.2019.151709
JALCOM 151709
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 24 April 2019
Revised Date: 31 July 2019
Accepted Date: 4 August 2019
Please cite this article as: S. Zhang, T. Sun, F. Ji, G. Dong, Y. Liu, Z. Li, H. Zhang, Q. Chen, X.
Liu, Electrical and magnetic properties of La Ag MnO (0 ≤ x ≤ 0.5) polycrystalline ceramics by
-x
1
x
3
combination of first principles calculations and experimental methods, Journal of Alloys and Compounds
2019), doi: https://doi.org/10.1016/j.jallcom.2019.151709.
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Electrical and magnetic properties of La Ag MnO
1
-x
x
3
(
0 ≤ x ≤ 0.5) polycrystalline ceramics by combination
of first principles calculations and experimental
methods
Shuai Zhang, Tao Sun, Fuquan Ji, Gang Dong, Yang Liu, Zhidong Li, Hui Zhang,
*
Qingming Chen, Xiang Liu
(School of Material Science and Engineering, Kunming University of Science and
Technology, Kunming 650093, Yunnan, China)
Abstract
In this work, electrical and magnetic properties of La Ag MnO (LAMO, 0 ≤ x ≤
1
-x
x
3
0
.5) polycrystalline ceramics with double−exchange (DE) effect and Jahn−Teller (JT)
distortion were studied using a combination of first principles calculations and
experimental methods. The GGA + U method was used to correct the self-interaction
error (SIE) that was encountered in first principles calculations. With the increasing of
Ag, energy band gaps (E or E ) of LAMO ceramics and the JT effect decreased, while
i
d
the DE effect was enhanced. LAMO polycrystalline ceramics (x = 0, 0.1, 0.2, 0.3, 0.4
and 0.5) were prepared by conventional sol−gel method in order to verify the
calculation results. The X−ray diffraction revealed that the structure of LAMO
ceramics transformed from single phase to multiphase as x was increased. The ρ−T
*
Corresponding author
E-mail address: lxjim@sina.com

curves suggested that the metal to insulator transition temperature (T ) and DE effect
p
were improved as x increased, which was in good agreement with the first principles
calculations. In addition, the temperature coefficient of resistance (TCR) at the peak
temperature (T ) and magnetoresistance (MR) at the peak temperature (T ) were
k
m
-1
obtained with different x. For x = 0.5, the value of TCR and MR reached 8.58% K
and 21.6%, and the T , T and T were 304, 291 and 298 K, respectively, implying
p
k
m
that the electrical and magnetic devices of LAMO ceramics could operate at room
4
+
temperature (300 K). XPS results indicated that the concentration of Mn ion
4
+
3+
increased with increasing x. The ratio of Mn /Mn reached 1 ∶ 2, which had the
strongest DE and magnetoelectric coupling effect for x = 0.5.
Keywords: Electronic structure; Double−exchange (DE) effect; Temperature
coefficient of resistance (TCR); Magnetoresistance (MR)
1
. Introduction
Doped manganite based on R A MnO (R = rare−earth ion, such as La, Pr, Nd and
1
-x
x
3
A = divalent elements, such as Ca, Sr, Ba) polycrystalline ceramics have been
intensively studied [1-6] due to their interesting physical properties such as colossal
magnetoresistance (CMR) [7], metal−insulator (M-I) transition at room temperature,
thermoelectric properties [8-10], data storage and magneto refractive effect [11-13].
The double−exchange (DE) mechanism [14, 15] based on the Hund coupling of the eg
and t electrons played a key role in the understanding of perovskite magnetic and
2
g
3
+
4+
electrical properties, and hopping of e electrons between Mn and Mn ions.
g
However, Millis et al. [15] argued that the CMR in R A MnO polycrystalline
1
-x
x
3

ceramics could not be interpreted by DE alone, and various other factors such as
Jahn−Teller (JT) effect need to be considered. The JT effect changed the Mn−O bond
lengths and also introduced distortion in the MnO octahedron.
6
Recent studies have focused on divalent doping in LaMnO (LMO) polycrystalline
3
ceramics [2, 16, 17], However, compared with divalent doped manganites,
monovalent metal doping (such as Ag, Na, K) still need further investigation ascribing
to its significant electrical and magnetic properties. In addition, the monovalent
doping in LMO has similar CMR and M−I transition properties compared to divalent
doping, but different charge, spin and lattice interactions due to differences in valence
and ion size. The temperatures of M−I transition (T ) have also been studied from
p
1
80~340 K for La A MnO (A = Na, K, Ag) in previous studies [4, 12, 13, 18].
1
-x
x
3
However, among these polycrystalline ceramics in La A MnO , there haven’t been
1
-x
x
3
detailed studies focusing on room temperature T or the combination of DE and JT
p
effects. Thus, in this paper, the effect of Ag doping LMO on structural and electronic
transport properties were studied using a combination of experimental methods and
first principles calculations. High TCR and MR near room temperature were obtained
for La Ag MnO (LAMO) polycrystalline ceramics. The Cambridge sequential total
1
-x
x
3
energy package (CASTEP) code, and general gradient approximation (GGA) with
Perdew−Burke−Ernzerhof (PBE) from first principles were carried out [19]. In order
to correct for the self-interaction error (SIE), the GGA + U approach [20-24] was
adopted to improve the accuracy of calculations, with U = 2.5 eV being applied in the
Mn 3d state. The total and partial electronic densities of states (DOS, PDOS)

suggested that the DE and J−T effect intensified and diminished with increasing x,
respectively, which was in consistent with the experimental ρ−T curves.
2
. Method and details
.1. Computation details
2
Fig.1. Schematic of unit cell structure of LAMO (x = 0, 0.3, 0.5) for first principles calculations.

(a) x = 0.3
a
b
g
c
d
e
-
23578.20
-23578.50
x = 0.3
f
h
-
-
-
-
23578.80
23579.10
23579.40
23579.70
i
a
a
b
c
d
e
f
g
h
(b) x = 0.5
Structure
a
b
c
d
e
-
-
-
-
-
-
-
26601.30
26601.60
26601.90
26602.20
26602.50
26602.80
26603.10
x = 0.5
f
g
a
b
c
d
e
f
Structure
Fig.2. La/Ag relative configurations structures and energy as a function of structure for LAMO (x
0.3, 0.5) ceramics, respectively. (a): x = 0.3, different Ag atom location structure (a ~ h) and
=
energy versus structure curves (i) for LAMO ceramics. (b): x = 0.5, different Ag atom location
structure (a ~ f) and energy versus structure curves (g) for LAMO ceramics. Here, La and Ag
atoms represent in green and dark red colors, respectively.
As shown in Fig 1, the sol−gel method was used for experiments and calculations
were performed based on density functional theory (DFT) for LAMO crystal
rhombohedral structure with space group R3c . The electronic structure of LAMO

was investigated theoretically by first principles using the GGA + U approach. In
order to obtain the most stable structure from first principles calculations, different
La/Ag ratios were considered for LAMO (x = 0.3, 0.5) ceramics, as shown in Fig 2.
The energy as a function of structure was also studied, as shown in Fig 2 (a) i and (b)
g. Since the structures of d for x = 0.3 and c for x = 0.5 had the lowest energy, and
they were chosen for the calculations for this work. The different proportions of La
atoms in the A site were substituted by Ag for LAMO perovskite structure [17, 20].
All calculations were carried out by the CASTEP code, and utilizing the GGA (PBE)
with Coulomb correlations (U = 2.5 eV). We employed a 1×1×1 unit cell LAMO
rhombohedral perovskite with lattice parameters a = b = 5.518 Å and c = 13.355 Å,
which contained 12 La atoms, 16 Mn atoms and 18 O atoms, as shown in Fig 1. The
cut−off energy of 500 eV and a 5 × 4 × 5 Monkhorst−pack k−point mesh in the
Brillouin zone were employed to obtain the reliable calculation results. In addition,
the electronic and ionic convergence tolerance for geometry optimization was set to 5
-6
×
10 eV and 0.01 eV/Å, respectively. The maximum stress within 0.02 GPa, and the
-4
max displacement using 5 × 10 Å.
.2. Experimental method
Bulk polycrystalline LAMO (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) ceramics were
prepared by the sol−gel method. The starting materials composed of La(NO ) ·nH O
2
3
3
2
(
99.99%, from sinopharm chemical reagent), Mn(NO ) aqueous solutions (50% by
3 2
mass, from sinopharm chemical reagent) and AgNO (from sinopharm chemical
3
reagent), were dissolved in 200 ml deionized water under continuous stirring. Citric

acid and ethylene were used as complexing and polymerizing agents, respectively.
The mixture was heated until a foamed gel was formed by magnetic stirrers. Then, the
foamed gel was dried at 140 °C for 12 h and ground into powders. The powders were
then pre−sintered at 900 °C for 12 h and pressed into pellets at a pressure of 16 MPa.
Finally, pellets were synthesized at 1100 °C for 12 h.
The structure of the prepared LAMO ceramics was characterized by X−ray
diffraction (XRD, Rigaku Ultima IV) measurements with Cu K radiation. The grain
α
sizes and morphology were examined by field emission scanning electron microscopy
(FESEM, HITACHI, SU8010). The electromagnetic performance indicators were
measured by conventional four−probe method at temperature ranging from 100 to 320
K and external field of 1 T using Keithley Instruments. X−ray photoemission
spectroscopy (XPS) was employed to study the stoichiometry and valence state of
polycrystalline ceramics.
3
. Results and discussion
.1. Calculation of electronic structure
3

LaMnO3
La Ag MnO
La Ag MnO
0.5 0.5 3
0.7
0.3
3
4
2
0
2
4
4
2
4
2
0
0
-
-
-2
-4
-2
-4
G
F
Q Z
G
G
F
Q Z
G
G F
Q Z
G
Fig.3. Band structure for La Ag MnO (x = 0, 0.3, 0.5)
1
-x
x
3
1
8
9
0
9
(a)
(b)
(c)
-
-
-
-
18
1
8
9
0
9
-
18
1
8
9
0
9
-
18
-4
0
4
8
Energy (eV)
Fig.4. Density of states (DOS) of different Ag doping level for LAMO: (a) LaMnO , (b)
3
La Ag MnO and (c) La Ag MnO .
0
.7
0.3
3
0.5
0.5
3

3
2
1
0
1
2
3
2
Ag 3d & 4s
Ag 3d & 4s
4
2
0
2
4
8
4
0
1
0
-
-
-
-1
-2
-
-
3
8
-3
8
O 2p
O 2p
O 2p
4
0
4
8
8
4
0
4
8
4
0
-
-
-4
-8
6
-4
-8
6
Mn 3d & 2p
Mn 3d & 2p
Mn 3d & 2p
3
3
0
0
-
-
-3
-6
-3
-6
-
6
-3
0
3
6
-6
-3
0
3
6
-6
-3
0
3
6
Energy (eV)
Energy(eV)
Energy(eV)
(a) LaMnO3
(b) La Ag MnO
(c) La Ag MnO
0.5 0.5 3
0.7
0.3
3
Fig.5. Partial DOS (PDOS) of LAMO (x = 0, 0.3, 0.5): (a) LaMnO , (b) La Ag MnO , and (c)
3
0.7
0.3
3
La Ag MnO . For Ag and Mn orbital DOS, the black and the red curves represents the 4d, 4s
0.5
0.5
3
and 3d, 2p orbitals, respectively.
Table.1.
Indirect (E ) and direct energy band gap (E ), Mn magnetic moment and average atomic partial
i
d
charge (q) from band analysis for LAMO (x = 0, 0.3, 0.5) polycrystalline ceramics.
x (mol%)
Ei (eV)
0
0.3
0.5
1.29
1.51
4.06
0.62
0.0
0.37
0.79
3.63
0.68
0.22
0.06
0.23
3.33
0.74
0.38
Ed (eV)
µMn (µB)
qMn (e)
qAg (e)
The band structure, Mn magnetic moment and average atomic partial charge (q)
obtained from first principles for LAMO (x = 0, 0.3 and 0.5) are shown in Fig 3 and
Table 1. From the band structure it is evident that all the structures exhibited
insulating characteristics. The direct band gap (E ) was ~1.51, ~0.79 and ~0.23 eV
d

for x = 0, 0.3 and 0.5, respectively. This decrease of band gap with increasing x can be
attributed to the change of spin polarization that resulting in a faint splitting of Mn 3d.
Meanwhile, E of 1.51 eV for LMO was in good agreement with previous
d
experimental reports, which were in the range of 1.1~2.0 eV [25, 26], and also similar
to the previous calculation studies which reported values of 1.427 eV [24], 1.21 eV
[
27] and 1.64 eV [23]. In addition, as x increased, the Mn magnetic moment (µB)
decreased from 4.06 to 3.33 µB. The average atomic partial charge (q ) increased
Mn
from 0.62 to 0.74 e with Ag contents increasing, indicated that Ag doping results the
4
+
concentration of Mn3+ decreased and Mn enhanced.
The DOS and PDOS (Ag, O, Mn) for the different of x are shown in Fig 4 and Fig 5.
1
2
By combining with Fig 3, it was clear that the Mn e ( eg and eg↑ ) splitting
g
↑
reduced with increasing x, and hybridization between Ag 4d and O 2p orbitals
1
g↑
2
enhanced. The Mn
e
and eg↑ orbitals located at the top of valence and the
3
bottom of conduction band, and O 2p orbitals above Mn t2 states dominated the
g
3
valence band. Mn t2 orbitals shifted to low energy in valence and conduction band.
g
2
1
g↑
In addition, the energy separation of E( eg↑ ) – E(
e
) resulted from the JT splitting
) corresponded to the indirect
2
1
g↑
band based on previous work [28]. E(eg↑ ) – E(
e
band gap (E ) and decreased from 1.29 to 0.06 eV, which suggested that the JT effect
i
diminished with increasing x. The DE effect based on the Hund coupling between Mn
3
2 g
eg and
t
electron was also studied as a function of x, as shown in Fig. 5. Due to
3
2 g
the strong orbital overlap of Mn e and O 2p, the energy difference between Mn
t
g
3
and O 2p orbital was regarded as the energy difference between Mn t2 and e . As a
g
g

3
result, Mn t2 and O 2p were respectively shifted to low energy and high energy in
g
valence band as x increased. This indicated that the energy difference between Mn
3
t2 and O 2p orbital was augmented. Therefore, the energy difference of the Hund
g
3
2 g
coupling between e and
t
increased, and indicated DE effect was enhanced.
g
3
.2.
Analysis of structural
La Ag MnO ceramics
∗ : Ag (PDF#04-0783)
(
a) 1-x
x
3
s : Mn O4 (PDF#24-0734)
3
*
x = 0.5
∇
*
*
x = 0.4
x = 0.3
x = 0.2
x = 0.1
x = 0.0
Mn O4
3
Ag
20
30
40
50
60
70
80
2θ (°)

(
b)
x = 0.5
x = 0.4
x = 0.3
x = 0.2
x = 0.1
x = 0
31.5
32.0
32.5
33.0
33.5
34.0
2
θ (°)
La Ag MnO ceramic
0
.9
0.1
3
(c)
Yobs
Ycal
Bragg position
Ydiff
2
0
30
40
50
60
70
80
2
θ(°)
Fig.6. (a). X-ray diffraction patterns of the LAMO (x = 0~0.5) polycrystalline ceramics. (b).
Enlarged plot of main peaks in the 2θ range of 31.5~34 °. (c). Rietveld refined X−ray diffraction
pattern of La Ag MnO polycrystalline ceramics.
0
.9
0.1
3
Table.2
The experiments and calculation for LAMO (x = 0, 0.3, 0.5) structure parameters lattice constant,
cell volume, Mn−O bond length and angles and the R−factors of Rietveld
LaMnO3
Exp/Cal
La Ag MnO
La Ag MnO
0.5 0.5 3
0.7
0.3
3
Structure parameters
Exp/Cal
Exp/Cal

a (Å)
b (Å)
c (Å)
5.518/5.663
5.518/5.662
13.355/13.577
352.227/383.069
1.36
5.513/5.654
5.513/5.654
13.358/13.669
351.630/371.071
1.34
5.509/5.540
5.509/5.539
13.359/13.743
351.011/364.652
1.32
3
V (Å )
rA> (Å)
<
dMn-O (Å)
ꢀMn-O-Mn (°)
Rp (%)
Rwp (%)
Rb (%)
χ
1.967/2.089
162.184/155.500
4.411
1.965/1.985
162.187/154.496
4.708
1.964/1.984
162.188/159.833
5.912
5.797
6.400
8.075
5.389
5.416
5.291
1.158
1.397
2.320
XRD was performed for LAMO (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) polycrystalline
ceramics. As seen in Fig 6 (a), unmarked peaks belong to perovskite structure LAMO,
and marked peaks correspond to metal Ag with Mn O phase. It was clear seen that
3
4
the Mn O (PDF⋕24-0734) phase occurs in the LAMO compound by Ag doping. At
3
4
low Ag contents (0 ≤ x ≤ 0.2), the structure was mainly composed of perovskite
structure phase and Mn O phase. However, for x≥0.3, the metal Ag phase
3
4
(
PDF⋕04-0783) occurs in LAMO ceramics were composed of perovskite, Mn O and
3
4
metal Ag phase. These results suggested that the solubility limit of silver was around
.3, which was in accordance with the different works of the literature had reported
13, 18, 29]. All polycrystalline ceramics exhibited rhombohedral perovskite phases
0
[
with R3c space group, as shown in Fig 6 (b). The XRD Rietveld spectra of
La Ag MnO were studied, as shown in Fig 6 (c). Also, the results for Rietveld
0
.9
0.1
3
R−factors and structural parameters for LAMO (x = 0, 0.3, 0.5) ceramics are shown in
Table 2. The LAMO structure (ICSD, 153552) to was used to fitting the XRD spectra

of x ≤ 0.2. At high Ag contents (0.3 ≤ x ≤ 0.5), the LAMO structure (153552, from
ICSD), metal Ag phase (PDF⋕04-0783) and Mn O (PDF⋕24-0734) phase were used
3
4
3
+
+
to fit the XRD result, respectively. Since La ion (1.36 Å) was substituted by Ag ion
(
1.28 Å), the average radius of A−site cation <r > decreased from 1.36 Å (x = 0) to
A
1
.32 Å (x = 0.5). Meanwhile, the parameters a, b and Mn−O bond length were slightly
shortened, whereas the parameter c and Mn−O bond angles showed minor expansion.
This resulted in a smaller volume of the LAMO crystal structure due to doping of Ag.
As the proportion of Ag doping enhanced, the changing of lattice parameters were
consistent with previous studies [29]. Moreover, the average size of B−site cation was
4
+
4+
reduced with the increase of Mn contents, since Mn ion (0.53 Å) is smaller than
3
+
Mn ion (0.645 Å). The change in
τ
τ
, is defined as:
rA + rO
=
(1)
2
(r + r )
B O
Where r represents the radius of i ions, also play an importance role in Mn−O bond
i
angles, leading the distortion of MnO octahedron. Meanwhile, the parameters a, b
6
and c based on DFT calculation of bulk structure LAMO (x = 0, 0.3 and 0.5) are also
presented in Table 2. Comparing experiment with calculation results showed that a
and b decreased from 5.518 to 5.510 and 5.663 to 5.540 Å for experiment and
calculation results, respectively, as x varied from 0 to 0.5. The parameter of c showed
a minor increase. As a result, the trend change of parameters calculations was in a
good agreement with our experimental results.

(a)
(c)
(e)
x = 0
(b)
(d)
(f)
x = 0.1
2
µm
2
µm
x = 0.2
x = 0.3
2
µm
2 µm
x = 0.4
x = 0.5
2
µm
2 µm
Fig.7. SEM images of La Ag MnO samples. (a)~(f) represent x = 0~0.5, respectively.
1
-x
x
3
The surface morphologies of La Ag MnO (0 ≤ x ≤ 0.5) samples at the same
1
-x
x
3
magnification of 2 μm as shown in Fig 7(a)-(f). All samples displayed preferable
compactness with few pores, and fine crystalline was obtained. The crystallinity was
improved with Ag doping. The grain sizes were controlled by the doping addition,
+
which the increased of grain sizes with Ag doping increases were observed. In
addition, the grain sizes have an effect on the number of grain boundaries, in turn

change the resistivity of La Ag MnO samples.
1
-x
x
3
3
.3.
Electrical transport and magnetic properties
0
0
0
0
0
0
.55
.44
.33
.22
.11
.00
0
0
0
0
0
0
.0 ( 251 K, 0.52)
.1 ( 274 K, 0.46)
.2 ( 293 K, 0.16)
.3 ( 295 K, 0.12)
.4 ( 301 K, 0.10)
.5 ( 304 K, 0.04)
0.16
0
0
0
0
.12
.08
.04
.00
9
0
120
150
180
210
240
270
300
330
T (K)
Fig.8. Plot of electrical resistivity as a function of temperature at 0 T for LAMO (x = 0~0.5).
The resistivity as a function of temperature for LAMO ceramics in the temperature
range of 100 to 320 K is shown in Fig 8. The peaks value of resistivity also listed in
Fig 8. All ceramics exhibited ferromagnetic metallic property at low temperatures
(dρ
/dT > 0) and paramagnetic insulator characteristics at high−temperatures (d
ρ/dT <
0
). The polaronic effect made the e and t electrons to have the same spin alignment
g
2g
and displayed ferromagnetic metallic behavior at low−temperature. In contrast, for
paramagnetic insulator behavior, the spin electrons were disordered between e and t2g
g
orbitals at high−temperature. Furthermore, as x was increased, the Mn e electrons
g
transitioned from localized state to delocalized state, thereby leading to an increase in
the conduction electron density of polycrystalline ceramics. It should be noted that the
resistivity occurs sharp decrease at x ≥ 0.2. The reasons might be caused by the

uniformly of grain sizes and grain boundaries. In Fig 7, we can see that the grain sizes
were much uneven for x = 0 and 0.1. As x increasing (0.2 ≤ x ≤ 0.5), the grain sizes
grow more evenly than low Ag contents, thereby might be result the reduction of the
grain boundaries and grain boundaries scattering. The resistivity of LAMO decreased
from 0.52 for x = 0 to 0.04 for x = 0.5. Meanwhile, the T increased from 251 K for x
p
=
0 to 304 K (room temperature 300 K) for x = 0.5. Based on previous studies [30, 31],
the JT and DE effect play an important role in insulators and metallic behavior,
respectively. T improved with increasing x, and the JT and DE effect receded and
p
enhanced, respectively. It was also in a good agreement with our calculation results.
8
(
291 K, 8.58 %)
x = 0.5
x = 0.4
x = 0.3
0
8
(
288 K, 7.03 %)
0
4
0
(280 K, 4.62 %)
(278 K, 3.78 %)
4
0
x = 0.2
x = 0.1
x = 0
4
0
(267 K, 3.89 %)
4
0
(244 K, 4.46 %)
220
240
260
280
300
320
T (K)
Fig. 9. The TCR (%) as a function of temperature for LAMO (x = 0~0.5) polycrystalline ceramics.
The TCR (%) as a function of temperature for LAMO (x = 0~0.5) ceramics is
shown in Fig 9. The TCR is defined as follows:
1
dρ
TCR = ( ×
)×100%
(2)
ρ
dT

where, ρ and T are resistivity and temperature, respectively. With increasing of x, the
TCR peak temperatures (T ) increased from 244 K for x = 0 to 291 K for x = 0.5. The
k
values of TCR decreased first and then increased, from 4.46 % for x = 0 to 8.58 % for
x = 0.5. At x = 0.5, the TCR reached a maximum value of 8.58% and T reached room
k
temperature (291 K). The peak TCR value depends on many factors, including
sintering temperature, preparation method, grain sizes, the tolerance factor τ and the
resistivities of the samples. At low Ag contents (0 ≤ x ≤ 0.2), the reduction of TCR
values might be caused by the replacement of La ion by Ag results in a decrease of the
tolerance factor τ. As Ag content increased to a certain extent (x > 0.2), the influence
of resistivity and grain sizes play a dominant role in the peak TCR values. The
samples resistivities significant reductions and grain sizes were improved, which
leaded to the peak TCR values increased. In addition, the Ag occurs in the form of the
second phase at grain boundaries and interfaces open a new channel for the electron
transport, which leading to decreases the
ρ of the samples and TCR increased.
Meanwhile, based on previous reports [32], increasing the conductivity along with an
enhanced DE effect should gradually increase TCR. These data suggested that high
TCR value of this report polycrystalline ceramics could potentially impact their
applications in uncooled bolometers or infrared detectors at room-temperature.
The MR is defined as:
ρ0 − ρH
MR(%) = (
)×100%
(3)
ρ0
where, ρ0 and ρH are resistivity at 0 and 1 T magnetic field, respectively. The MR

versus temperature for LAMO (x = 0~0.5) is shown in Fig 10. A magnetic field of 1 T
3
+
4+
resulted in the increased ordering of electron spins of Mn and Mn , and it was
3
+
4+
easier for electrons to transition between Mn and Mn ions as compared to the 0 T
case. Thus, the resistivity at 0 T was higher than 1 T. The MR curve displayed a
similar variation with increasing temperature, which it initially increased and then
decreased. T increased from 248 K (x = 0) to 298 K (x = 0.5), which was obtained at
m
room temperature. The values of MR decreased from 31.3% (x = 0) to 21.6% (x = 0.5)
at room temperature. Two types of MR have been confirmed in perovskite manganites
oxides, intrinsic and extrinsic MR, which induced by DE effect and tunneling effects
between the grain boundaries (GBs), respectively. It was noted that the spin−polarized
tunneling phenomenon for GBs play a key role in the MR properties, because of the
values of MR were decreases gradually with GBs increasing. Meanwhile, based on
previous research [1, 33], the spin−polarized tunneling phenomenon could have an
important influence on MR, and the enhanced spin disorder with increasing x led to
lower MR. Meanwhile, the diamagnetic feature of Ag was also one of factor for the
lowering of MR.
30
(
a) x = 0
(b) x = 0.1
30
24
18
12
0.5
0.4
0.3
0.2
0.1
0.0
0
0
0
0
.5
.4
.3
.2
0 T
25
0 T
1
T
1
T
20
0.1
.0
0
15
150
200
T (K)
250
100
150
200
T (K)
250
300
10
180
200
220
T (K)
240
260
180
200
220
240
260
280
T (K)

2
1
1
4
8
2
6
(
c) x = 0.2
(d) x = 0.3
2
4
6
8
0
0
.12
0.16
0
1
T
T
0 T
1 T
0.12
0.08
0.08
0.04
0.00
1
0
.04
0.00
1
00 150 200 250 300 350
T (K)
100 150 200 250 300 350
T (K)
1
60
200
240
280
320
150
200
250
T (K)
300
T (K)
2
4
6
8
0
(
e) x = 0.4
(f) x = 0.5
2
0
0
0
0
0
0
.10
.08
.06
.04
.02
0
1 T
T
0.040
0
1
T
T
0.032
0.024
0.016
1
15
10
0.008
0.00
1
00 150 200 250 300 350
T (K)
1
00 150 200 250 300 350
T (K)
5
200
250
300
350
200
250
T (K)
300
350
T (K)
Fig. 10. The MR (%) as a function of temperature for LAMO (x = 0 ~ 0.5) samples at 1 T
magnetic field. (a~f) represent the doping x = 0~0.5, respectively. The inset graph is ρ−T curves
under different magnetic field (0 T, 1 T).
A summary of the T , T , T , TCR and MR with the different of x level is shown in
p
k
m
Table 3. Results indicated that the T , T , T , TCR and MR could be controlled by the
p
k
m
doping x level. With the increasing x, the T , T , T and TCR were augmented but MR
p
k
m
declined. At x = 0.5, the high TCR (8.58 %) and MR (21.6 %) were obtained at room
temperature, which means that the LAMO ceramics could be used for photoelectric or
magnetic devices at room temperature.
Table. 3.
The values of T , T , T , TCR and MR for LAMO (x = 0 ~ 0.5) polycrystalline ceramics.
p
k
m
x (mol%)
(K)
0.0
251
0.1
0.2
0.3
0.4
0.5
T
p
274
293
295
301
304

TCR (%)
Tk (K)
4.46
244
31.3
248
3.89
267
28.5
272
3.78
278
22.1
284
4.62
280
23.8
286
7.03
288
21.7
292
8.58
291
21.6
298
MR (%)
Tm (K)
3
.4 Analysis of XPS results
The XPS spectra of Mn 2p and Ag 3d levels shown in Fig 11 indicate that the
doping of Ag was successful in the LMO ceramics. For Fig 11 (a), as x = 0, the
binding energies (BE) of Mn 2p1/2 and Mn 2p orbital were 653.38 eV and 641.73 eV,
3/2
respectively. For x = 0.5, the BE of Mn 2p1/2 and Mn 2p3/2 levels were 653.13 eV and
6
41.63 eV, respectively, as shown in Fig 11 (b). Compared to x = 0, the BE of Mn
p1/2 and Mn 2p3/2 orbitals for x = 0.5 shifted to lower energy. In addition, as shown in
2
Fig 11 (a) and (b), the value of BE Mn 2p3/2 level was between the Mn O (641.4 eV)
2
3
4+
3+
and MnO (641.8 eV), which was indicative of Mn ions existing as Mn and Mn .
2
The fitting curve for different of x level doping was also measured. The concentration
4
+
3+
4+
of Mn in (Mn + Mn ) was estimated to 20.54% and 33.29% for x = 0 and 0.5,
4
+
3+
respectively. Thus, ratio of Mn /Mn was characterized from 1 : 4 for x = 0 to 1 : 2
4
+
for x = 0.5, which indicated that the concentration of Mn increased and DE effect
enhanced with the increasing of x. Furthermore, the volatilization of Ag might leading
to the formation of the vacancies on La and O sites, these also play an important role
in the valence state of Mn. Meanwhile, the XPS spectra for x = 0 and 0.5
polycrystalline ceramics was determined, the different elements orbital were labeled
in Fig 11 (c). The replacement of La ion by Ag results in a decrease of the La 3d and
3
/2
0
+
3
d level for x = 0.5, And the Ag and Ag level occurs for x = 0.5 compared to x = 0,
5/2

which was good agreement with XRD results. Otherwise, in order to obtained the
existence form of Ag for x = 0.5, the Ag 3d level spectrum was measured for x = 0.5
as seen in Fig 11 (d). The BE of Ag 3d3/2 and Ag 3d5/2 orbitals were 374 eV and 368
eV, respectively. Based on previous studies [34-36], the BE of Ag 3d5/2 was between
0
+
the value for Ag (368.7 eV) and Ag (367.6 eV), which indicated that the metal Ag
+
and Ag coexisted for x = 0.5. Meanwhile, the difference of binding energy between
Ag 3d3/2 and Ag 3d5/2 was 6.0 eV, which indicated that the metal Ag existed in x = 0.5
[
37]. This was also in agreement with XRD patterns.
Expt Data
Expt Data
(
a) x = 0
(b) x = 0.5
3+
3+
Mn
Mn
Mn
Mn2p3/2
Mn2p3/2
4+
4+
Mn
Backgnd
Fitting Curve
Backgnd
Fitting Curve
Mn2p1/2
Mn2p1/2
660
655
650
645
640
635
630
660
655
650
645
640
635
630
Binding energy (eV)
Binding energy (eV)
x = 0
x = 0.5
(
c)
(d) x = 0.5
Ag3d
△
E = 6.0 eV
Ag3d5/2
3
68 (eV)
Ag3d3/2
3
74 (eV)
1000
800
600
400
200
0
380
375
370
365
360
Binding Energy (eV)
Binding energy (eV)
Fig. 11. (a), (b) Mn 2p levels spectra and fitting curve for LAMO (x = 0 and 0.5), respectively. (c)
XPS spectra for LAMO (x = 0 and 0.5) and (d) Ag 3d level spectra for LAMO (x = 0.5).

4
. Conclusions
In summary, the electronic structures of LAMO (x = 0, 0.3, 0.5) polycrystalline
ceramics with rhombohedra structure were calculated by CASTEP with DFT by first
principles calculations method, using the GGA + U within PBE approach. The band
gap and DOS were also studied for LAMO ceramics. For x = 0, 0.3 and 0.5, the E and
i
Ed were 1.29, 0.37, 0.06 eV and 1.51, 0.79, 0.23 eV, respectively. The PDOS indicated
2
1
g↑
that the energy difference of E( eg↑ ) – E(
e
) decreased and Hund coupling between
Mn e and t increased with increasing x. Correspondingly, the JT and DE effect
g
2g
decreased and enhanced, respectively. LAMO (x = 0~0.5) polycrystalline ceramics
were prepared by the sol−gel method in order to verify the first principles calculations
results. The structure, electrical and magnetic properties of LAMO samples were
studied in details. XRD results showed that all polycrystalline ceramics were
rhombohedra structure with R3c space group, and a single phase to multiphase
transition was observed. For x < 0.3, the ceramics were only composed of perovskite
phase. For x ≥ 0.3, multiphase characteristics were obtained with perovskite phase,
metal Ag and Mn O . The experimental and calculations results on the crystal
3
4
structure suggested that the doping of Ag led to a volume reduction of LAMO
ceramics, wherein the Mn−O bond length was found to decrease and angles were
expanded. In addition, ρ−T curves were studied as a function of x. Results showed
that the T improved and DE effect enhanced, which was in good agreement with the
p
calculation results. Furthermore, as x increased, T , T and T increased, the TCR
p
k
m
decreased first and then increased, and the MR declined gradually. At x = 0.5, T , T
p
K

4+
3+
and T were 304, 291 and 298 K near room temperature. Furthermore, the Mn /Mn
m
4
+
amount was studied by XPS, where an enhanced concentration of Mn was obtained
4
+
3+
with increasing of x. The value of Mn /Mn was 1 : 4 for x = 0 and 1 : 2 for x = 0.5.
This indicated that LAMO ceramics had the strongest DE effect at doping level x =
4
+
3+
4+
3+
0
.5, where Mn converted into Mn (Mn /Mn ratio at 1:2). These results suggest
promising applications of LAMO polycrystalline ceramics in photoelectric or
magnetic devices at room temperature.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of
China (Grant no. 11674135), the Analysis and Testing Foundation of Kunming
University of Science and Technology (Grant no. 2018M20172130001), and the
Innovation Training Program for College Students, (Grant no. 20180179).
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[
9
[
7

1
2
3
4
. Electromagnetic properties of LAMO were explored by
abinitio/experimental methods.
-1
. TCR and MR reached 8.58% K and 21.6% as T and T at 291 and
k
m
2
98 K respectively.
. DE and JT were used to explain improvement of electromagnetic
properties for LAMO.
. The results indicated promising applications of LAMO in room
temperature devices.